There are many ways to implement the arithmetic of ℤ modulo nℤ in Python.
A class with an __init__(self, k, n) for the ring element k mod n
is awkward to use because the modulus n is fixed for all members of the ring
but must be passed as an argument for each new object.
Python's baroque interpretation of object oriented programming has the
obscure __init__subclass__ class method. It's called in the
parent class when a derived class's object is constructed.
This lends itself to the following (very abridged and bowdlerised):
class zmodn:
@staticmethod
def mk_init_sub(n):
def __init__sub(self, k):
self.k = k % n
self.n = n
return __init__sub
def __init_subclass__(cls):
name = cls.__name__
u = name.rindex("_"); clsmodstr = name[u+1:]; clsmod = int(clsmodstr)
cls.__init__ = zmodn.mk_init_sub(clsmod) # inject constructor
def __add__(self, other): return self.__class__(self.k + other.k)
def __neg__(self): return self.__class__(-self.k)
def __sub__(self, other): return self + (-other)
# ....
It does the following: if a class inherits from zmodn__init__subclass__ gets called with the new class (as an object).
It parses the __name__ of the class from the right to find an
underscore, and casts everything right of it into an int as clsmod.
The newly created class gets an autogenerated __init__ method,
which contains clsmod as closure.
Example code
class ring_12(zmodn): pass
two = ring_12(2)
six = ring_12(6)
zero = two*six
The whole zmodn.py has
some more methods and injects a __truediv__ operator in classes where
the modulus is prime.
When using ForwardAgent with SSH,
the local ssh-agent can be used to
authenticate connections from a remote system jumphost to a third.
Problems with this are
that the forwarded connection to the local agent might be abused by root
on the remote machine to login as the legitimate user on still other systems.
that the agent can hold more keys than the third system will accept, and tries
them in a fixed order.
Problem 1 can be mitigated by adding the relevant keys with
ssh-add's -c
Option, so that each use of the keys activates a dialog asking for permission.
Trying to log into a third machine from jumphost and getting the error
Too many authentication failures
is the result of Problem 2. It happens when there are more than six keys added
to the agent, and the relevant key for the third system is not in one of the first
six.
If the agent was used from the local machine,
it would be sufficient to add a specific IdentityFile
and the IdentitiesOnly yes Option. But on the remote system
there are no secret keys, because that was the whole point of the Agent Forwarding.
ssh-add -l lists all the keys in the agent, but there seems to
be no way to specify which of those to use in ssh third_system.
A workaround that i discovered recently is running a second ssh-agent
on its own SSH_AUTH_SOCK,
adding the relevant keys for the remote system to just that agent, and
forwarding only that agent's socket. It works like this:
The -a Option of
ssh-agent lets it listen on the given UNIX socket.
The ForwardAgent
allows to explicitly specify the socket to forward to the remote machine.
If i want to connect directly to the third system from local, i can use the
IdentityAgent
Option on my local .ssh/config to use the non-std agent:
The lack of options to select forwarded keys on the jumphost is a bit disappointing,
but the tooling for running alternative agents is good enough for my scenario.
smart-quotes.el
smartly enables automatic insertion of correctly curled single or double quotation
marks in emacs.
This is typographically nice, but can be deadly in Unicode-enabled programming
languages where a "string starting with a dumb-quote, but terminated by a smart one”
is unterminated for the parser but looks terminated for the human reader.
And pressing C-v at front/end of every string gets exhausting.
But what about literate programming, as for example in org-babel
codeblocks? The buffer is in org-mode, definitely not a programming
mode, but the blocks inside #+begin/end_src are:
* About strings
[...] Some “smart” statement about /strings/
#+begin_src
s = "dumbly quoted string";
...
#+end_src
org-mode has a predicate to check if point is inside such a code block,
named org-in-src-block-p, but how to use it without rewriting
smart-quotes.el?
Emacs' lisp advice-add to the rescue!
This is Aspect-oriented programming,
where a function g is wrapped in another function f.
It has a
:before-until “combinator”, which evals g only
if f returns nil when run with g's parameters.
In Περὶ Ἑρμηνείας Aristoteles defines the basic terms of his logic to
be single predicates, each of single subjects
see for example the Stanford Encyclopedia of Philosophy
This excludes all predicates of higher arity, e.g. two-place relations.
What effects does this restriction imply for the statements that can be
logically analysed and discussed?
Timelessness
As every predicate has only one argument, then if it holds at all,
it must hold eternally, because there is no possible second parameter
to serve as a timestamp or interval of validity.
So statements like Socrates is alive,
coffee is ready, the emperor of france is bald
are either true or false;
and if true at the time when their validity is checked, then they must be
true eternally.
The discourses using this logic are restricted
to timeless expressions.
It is impossible to examine processes.
Unrelatedness and separation
Since only unary relations are allowed, statements such as
Socrates is married to Xanthippe are inexpressible.
Aristotle is therefore unable to infer the valid
Xanthippe is married to Socrates, even if he would
somehow know the general rule If A is married to B, then B is married to A,
(or “Being married to” is a symmetric relation, which is expressible
in his logic).
Subjects can only be treated in isolation. In the resulting ontology
they are cut off from each other and from all context by the restrictions
of the underlying logic.
Inexpressability of basic mathematical concepts
Euclid's Geometry
Geometry concerns intersections of two (or more) lines, angles formed
by two lines, figures enclosed by three or more lines, etc. For example
Euclid's fifth postulate begins with if two straight lines lying in the same plane intersect a third [...].
The relation “line A intersects line B” cannot be formed from one-place
predicates. Although Aristotle uses these in his examples in Prior Analytics,
Posterior Analytics and Meteorologica, he'd be unable to formulate
them in his Logic.
Functions
The fundamental concept of a function cannot be expressed
in Aristotelian logic, because it requires at least two-place relations
(“f at x has value f(x)”). So even eternal
laws of Physics — like Newtons law of gravity — can (ironically) not be
stated with the logic of the author of Φυσικὴ ἀκρόασις.
Equivalence Relations
Since the late 19th century, many mathematical structures are
formally defined by equivalence relations on sets or classes
see for example The Search for Mathematical Roots, 1870-1940 by Ivor Owen Grattan-Guinness,
Princeton Univ. Press ,chapter 5, Paragraph 5.3.6.
These are two-place relations which are
reflexive : for every a: R(a,a)
symmetric : R(a,b) ⇒ R(b,a)
transitive : R(a,b) and R(b,c) ⇒ R(a,c)
For example the elements of the cyclic group of numbers modulo thirteen are defined
as the sets of all numbers having the same residue after division by 13.
So the thirteen elements are the quotient setsZ/R
n : R(n,0) : (..., -13, 0, 13, 26, 39, ...)
n : R(n,1) : (..., -12, 1, 14, 27, 40, ...)
n : R(n,2) : (..., -11, 2, 15, 28, 41, ...)
..
n : R(n,11) : (..., -2, 11, 24, 37, 50, ...)
n : R(n,12) : (..., -1, 12, 25, 38, 51, ...)
as defined by these relations.
Since two-place relations cannot
be used, most of modern mathematics is outside
the possible subjects of Aristotelian logic, although practically
all mathematical statements are timeless.
In the light of these findings, the broad adoption of Aristoteles' logic
in Western European theology and philosophy could be judged
an impediment to reasoning about practically any non-trivial subject.
This may sound harsh, but it was remarked before by much more distinguished
writers:
“The doctrine of the individual independence of real facts is derived
from the notion that the subject-predicate form of statement conveys a
truth which is metaphysically ultimate. According to this view, an
individual substance with its predicates constitutes the ultimate type
of actuality. If there be one individual, the philosophy is monistic;
if there be many individuals, the philosophy is pluralistic. With this
metaphysical presupposition, the relations between individual
substances constitute metaphysical nuisances: there is no place for
them. Accordingly — in defiance of the most obvious deliverance of our
intuitive 'prejudices' — every respectable philosophy of the
subject-predicate type is monistic. The exclusive dominance of the
substance-quality metaphysics was enormously promoted by the logical
bias of the mediaeval period. It was retarded by the study of Plato
and of Aristotle.” A.N.Whitehead, Process and Reality(1929), p. 137
“Such investigations show very soon that traditional Aristotelian scholastic logic
is quite inadequate for this purpose [of finding a constitutive theory].” Neurath, Carnap and Hahn in
Wissenschaftliche Weltauffassung. Der Wiener Kreis (2012), F. Stadler.
“Another property, supposed to be equivalent to this one, though in reality not so, was the property of being deducible (in the sense just explained) from the law of contradiction, or, more generally, from what have been optimistically called "the laws of thought". Now formal logic, in the times when such views flourished, had no exact means of knowing what was deducible from what, having expended its slender store of exactitude and subtlety on the syllogism - a subject scarcely more useful or less amusing than heraldry.
”
Bertrand Russell in Necessity and Possibility(1905).
One nice feature of drawterm and Plan9's cpu and ncpu
is that parts of the local filesystem appear on the remote machine as /mnt/term.
So instead of
ssh hostname
dang, forgot that file
open local shell in new tmux/xterm/screen
scp file hostname:
back to the shell with ssh hostname
do stuff on hostname
dang another file not there
back to the shell with the scp
scp anotherfile hostname:
one can simply do
drawterm hostname
cp /mnt/term/file .
do stuff on hostname
cp /mnt/term/anotherfile .
Can we do that over ssh, too?
One could try diverse trickery with sftp through FUSE,
or NFS/CIFS/WhateverFS exports.
I explored the following path closer to the Plan9 original:
Unix-like systems can run
u9fs
to export directories over 9p, and 9pfs to mount them.
Forwarding u9fs's in/output through ssh caused strange errors.
Using socat to bind the filedescriptors to a TCP socket on localhost
and forwarding that through ssh works.
The result is u9cpu.sh, which mounts a given directory (default $HOME/tmp)
as /mnt/term on the remote machine and then opens a shell there.
UPDATE Ron Minnich of Plan9 fame has implemented something similiar in Go: u-root/cpu.
Like almost everybody doing stuff with computers, I played
around with various monospaced fonts. Since the old days of
pixilated characters on green-glowing 25×80 terminals
a lot of effort has been put into usable fonts for programmers.
This went so far that hackers joined the ranks of font designers,
for example Raph Levien with his Inconsolata
and his other fonts, not to
forget his library Spiro which is
integrated in the open source fontdesign tool
fontforge.
Over the years I used Inconsolata, Vera Sans Mono and even
Meier's Syntax for
coding.
Recently I stumbled over — and subsequently bought — Operator (Mono), a typewriter-inspired font by the famous type designers at Hoefler & Co.
It's the only programmer's font with its own
documentary AFAIK.
At 36C3, Erwin Ernst Steinhammer gave a Talk (in German)
on lists of suspects
suspected of being gay
that the German police collected well before the Nazis' rise to power.
The police claimed that they had those lists just to keep their eye on the milieu.
When the nazis came to power they almost immediately used the lists to find and deport people
to concentration camps where most of them were killed.
Ernst's point in the talk is that a benevolent government must take care not to
aid a possible future extremist government by compiling lists of their prospective
victims.
This reminded me of the Holocaust documentation center in Oslo. It has a fantastic
piece of art just beside the entrance: a gigantic Hollerith punchcard.
It is an
art installation
by Arnold Dreyblatt based on work by William Selzer
on genocide and statistics.
What the Germans did after the occupation and installment of a puppet-regime under Quisling was to conduct a census of the Norwegian population. And they
used DeHoMAG, that is, IBM equipment.
(The Nazis did not need to search the census data to find, deport and kill Norwegian jews —
jewish religious organisations provided the Nazis with membership lists.)
The punchcards from the census became interesting when the Germans were looking for young Norwegian
men to conscript into labour service or the army.
And this is where history gets (even more) exiting. The Norwegian resistance knew about the German plans
and the punchcard technology. They tried to destroy the database i.e. the collection of punchcards,
but failed. They then proceeded to sabotage all of the
IBM 405 tabulating machines in Norway.
Dreyblatt's artwork has its own book Innocent Questions with texts by Willam Selzer on the
data gathering and subsequent analysis that typically preceeds genocides.
WGS84: 49.74306, 11.12948
This is a small detail from a war memorial in Weilersbach (49.74306° N 11.12948° E) erected closely following the second World War.
The whole plaque lists more than one hundred names.
As opposed to the revanchist, glorifying tone of other memorials, which were erected after the first World War,
this shows an expressionist harshness.
The font looks extremely severe. Every shape is reduced to rectangular
(except one little diagonal to distinguish D from O).
All font features that could remind of a living hand using a pen are removed.
Everything that would show the stonemason's art is avoided.
The ascenders are short and unadorned as if ducking behind a wall,
the primitive g's descender gives it the look of an open jaw.
The ch ligature (twice in Urschlechter, once in Hübschmann)
is remarkable in its simplicity. The whole design seems to state
A quick look at Georg Nees' computer-generated artwork Schotter made me code schotter.ps, a PostScript version of Schotter, which should look different every time it is rendered or printed (The picture below is an SVG of one possible rendering).
SUN Netra T5220: 64-threaded 8-core sun4v, 32Gb ECC RAM, four SAS Disk slots, two of them with 146Gb blank disks
Price in 2009: $22 000, got it for 100 Euros.
Nice. But the incompetent bungler who sold it forgot to mention that the
security-mode was set to command, and
he has got no password for it. So one cannot even change the
boot device. Fortunately the default is disk net, so installation from net to disk was possible.
How to reset the security-mode?
(The security-mode password is not the ALOM/ILOM password. Those are relatively easy to reset.)
Install Solaris or OpenSolaris or Indiana or Illumos?
Solaris11 has a usb disk image, but OBP disk is a devalias to the first SAS disk,
so USB is right out.
Take a Solaris disk image and write it to SAS disk on another machine.
Turns out that all machines at work have HP SmartArray controllers
that don't allow direct disk access, only RAID 0,1,6,10,..
Buy a RAID controller, put it in a PC, write image to SAS disk. But JBOD for an Adaptec ASR-5405
does not mean Just a Bunch Of Disks. It means Bunch of Disks the first blocks of
which are polluted with metadata by the controller and so cannot be used to boot
a system from a different controller. Idiots.
Install Solaris over the net.
Oracle and the copies of the ruins of OpenSolaris Webpages
only offer their Autoinstaller/Jumpstart which requires an Oracle/SUN Install server.
So: Set up a laptop with OpenSolaris as Install server. Installation fails because
the networked bootloader requires additional parameters from OpenBootProm to
select the image to be pulled by http/tftp in the next step. And the OpenBootProm is not
accessible because of security-mode. But wait! The ALOM service processor allows to set a bootscript along with the
logical domain selection to bootmode, perhaps one can put the parameters in the
bootscript? No, they are 64 chars maximum, of which 30 already eaten up by
setenv network-boot-arguments , and there are more required settings.
Even if the install server gets IP 1.1.1.1 and the path of the TFTP URL is just one letter,
the 64 chars do not suffice.
OpenIndiana or Illumos? Are x64 only, sparc64 port was dropped from the builds.
But there are at least two independent builds by sparc64 enthusiasts:
v9os and Tribblix.
But both supply ISO images only, and boot cdrom will not work, because
security-mode.
Learn how to setup logical domains (not entirely trivial).
Setup a logical domain with an actual (empty) SAS disk's block device as first vdisk
and a Solaris ISO image as the second vdisk, and no vnet.
Boot into control domain, connect to console of guest, discover that the logical domain's
openbootprom could not boot from the empty disk, but is permissive enough to accept boot disk1.
Boot the installer, install onto the physical disk.
Shutdown. Insert that disk in the first slot.
Boot. Discover that Solaris 10 refuses to mount the root zfs because the installer put
the physical location in the zpool metadata, and since the disk resides in a different slot now, the
metadata is incorrect. This is a known problem .
Booting from ALOM with bootmode bootscript="boot -F failsafe" results in a rootshell, zpool -f import rpool automatically resets the phys_path of the Zpool.
After a reboot into a a fully functional though historical Solaris system,
eeprom shows that the installation process had reset the security-mode to none.
So the problem was solved after step 5 above...
C-Keen used stem and
Flask's sendfile
for a small skript that creates a hidden service URL for a given
file and a flask instance to serve it.
And it is self-hostinghere.
Turns out not to be so easy: not every city (Q7930989) is a human settlement (Q486972), so take the UNION.
"Located in country" (P17) seemed the only reasonable relation of cities and countries, so iterate that over
Russia (Q159), Belarussia (Q184) and Ukraina (Q212)
but it turns out that at least Omsk (Q898) is not in the country of Russia (Q159) but instead
is an "instance of" (P31) an "administrative territorial entity of Russia" (Q192287),
so UNION over "administrative territorial entities" of Russia and Ukrainia.
Turns out that there is an "administrative territorial entity of Crimea", so who knows
what other non-orthogonal classifications people used to enter ex-Soviet cities into WikiData.
Not exactly promising.
UPDATE:
Omsk (Q898) is infact "in the country" (P17)
of Russia (Q159), my oversight.
UPDATE:
FILTER( LANG(?cityLabel)="en" ) is much wiser than to use the translation SERVICE.
Since you're not here to learn anything,
but to be taught
so you can pass these tests,
knowledge has to be organized
so it can be taught,
and it has to be reduced to information
so it can be organized.
Do you follow that?
In other words
this leads you to assume that organization
is an inherent property of the knowledge itself,
and that disorder and chaos
are simply irrelevant forces
that threaten it from outside.
In fact it's exactly the opposite.
Order is simply a thin, perilous condition
we try to impose on the basic reality of chaos.
The Shœstringfoundation has a long term project
to provide a distributed (*bing*), fault-tolerant (*bing*) storage system with
servers at several locations, accessible through IPv6 and TOR hidden services.
Tahoe LAFS will be the storage layer,
with a web frontend and SFTP for automated access and FUSE (where available).
A prototype is already running on servers in a
unique local address network
spread over several locations, connected by VPN tunnels.
What is missing is a stable IPv6 prefix to make the service reachable
for the rest of the world.
Experiences with SiXXs and german ISPs led me to the conclusion that
a provider independent prefix is needed.
The friendly folks at
openfactory in Switzerland
offered their help, for which i'm grateful.
Many german ISPs now “provision” their customers (i.e. practically everybody)
with IPv6-connected middleboxes that translate a non-routable IPv4 net at one end
to an address from a small pool of routable IPv4 addresses at the ISP. The IPv6 networking
is a side-effect.
Now everybody has IPv6 connectivity, it seems. But the german ISPs don't assign static v6 prefixes,
they change them periodically as they did with v4 addresses in the heydays of forced DSL disconnects.
The ISP that supplies uplink at my home has a /32 prefix. They could subnet this in 212 ways
to map their routing topology and still give out 220 static prefixes to their customers.
When asked nicely, they responded that they do not even consider it.
Why not? Because everybody could then run servers at home without paying extra for it, because
that's what End-to-End Internet was all about. And they make sure it is not going to happen, IPv6
or not. (See also artificial scarcity)
So people run tunnels to SiXXs (of fond memory) and hurricane electric to get decent IPv6 prefixes
through the already IPv6-enabled infrastructure of their providers.
Searching for ISPs around here that do hand out static prefixes was depressing. There are
high-profile providers with technically excellent offers
for commercial entities with a steady flow of earnings, but for a non-profit project they
are way too expensive (€ 250 and more per month).
Various Howtos about DKIM exist. After creation of a public/private keypair for signing, some
of them advise to insert a TXT RR of the following kind
into the zone file containing the affected mail domain:
I tried this with the NSD DNS server.
What i found the hard way:
The semi-colon (;) is the start-of-comment in zone files. Typing
the quoted line verbatim cuts off everything after k=rsa.
TXT records have a maximum length of 255 chars (because some length
field has only 8 bits), so even when the semi-colons above are masked with backslashes,
nsd (version 4.1.10) will refuse to load the zone file, but will not
explain why the parser thinks it is erroneous.
To get the TXT entry in the zone, one has to
surround the contents — beginning with k=rsa — with parens, and
split them into chunks of at most 255 characters, and
put these chunks into double-quotes, and
separate these with spaces
The resulting line in the zone file for the example above would be
TOR's hidden services are an extremely cool feature.
Not because people can hide their illicit websites (the Warez community
managed to do that decades before), but for other reasons:
Firstly,.onion addresses name services, not host interfaces. Tying interface
addresses of hosts to names and re-using them in URLs to point at services is a misdesign which leads
to such kludges as the Server header in HTTP/1.1 where the application
transmits which name it was using when initally connecting to the service.
So URLs map services to hostnames which map to IP addresses which have interfaces which have bound
services which get the unresolved
names again on the application layer to find out which service was actually addressed.
This makes it very complicated to move a service without fiddeling with DNS.
An .onion name does not have to ultimately resolve to a globally visible interface address.
Instead it identifies the tunnel-entry for a service which can be moved from machine to
machine as long as the hidden_service configuration is carried along.
Secondly,.onion addresses deliver what https URLs failed to,
namely mapping public keys to services uniquely.
There are no multi-rooted hierachies of CAs behind the name-to-key bindings, no obscure
ASN.1 based certificate schemes. An .onion address uniquely and automatically
identifies the service with the public/secret key pair involved in the key exchange.
There has been at least one attempt to build something similiar into IPv6 addresses
(RFC 3972), but implementations
are either missing or hidden in the darknet. And because connections inside
the tor network are always encrypted, one could even safely run a telnet daemon inside
a hidden service.
As a result of Secondly, Thirdly, .onion addresses are a barrier-free global namespace, without
absurd fees charged for bits in config-files, trademark disputes and the like.
I run at least one hidden service on each relevant machine to provide a MITM-safe entry point to services.
I have screen(1) running contineously on servers. On some
of them, the screen contains ssh-sessions to further machines. Because
i trust these servers less than my laptop, i don't store secret keys
there, i use AgentForwarding on the connection to the server and
ssh-add -c $relevant_key on the laptop, so i must confirm
each use of the key through the forwarding.
On disconnecting/reconnecting
to the server in question, the SSH_AUTH_SOCK variable
changes, but remains unchanged inside the long-running screen. ssh from
inside screen will prompt for passwords, because the
ssh-agent does not respond on the old path.
i found no clean solution to propagate the change to the
screen windows after re-attaching them.
So i put this in my .profile
on the server
test $SSH_AUTH_SOCK
if [ $? -eq 0 ]; then
if [ ! $SSH_AUTH_SOCK = "/tmp/ssh-agent-$USER-screen" ]; then
ln -sf "$SSH_AUTH_SOCK" "/tmp/ssh-agent-$USER-screen"
fi
fi
So all screen windows have SSH_AUTH_SOCK set
to the same path always, and when i connect to the server,
the shell soft-links that path to
the actual socket which is forwarded through ssh to
the ssh-agent on my laptop.
Requirements: a host with a running tor node, qemu,
some diskspace for the emulated system, install media for an OS on the emulated system
Result: a host with an .onion address, connectivity restricted to
TCP and no traceable IP address.
Start qemu with the following options
-net nic \
-net 'user,hostfwd=tcp::5555-:22,restrict=on'
The emulated machine will have a network interface
unconnected to anything, autoconfigured to 10.0.2.15/24.
Qemu will forward connections to localhost:5555 to sshd
on the emulated machine.
Create a user on the emulated system and install wlogdsocks-torify
or some other socksifier that forwards DNS requests.
On the machine hosting the qemu forward the local tor port to
the emulated system:
ssh -nN -R9050:localhost:9050 -l user -p 5555 localhost &
The emulated system can now reach TCP services through
socksified programs, e.g.
dsocks-torify.sh sh
wget http://example.com/a_file
scp a_file bob@example.org:
On the machine hosting the qemu create a hidden service by
adding the following lines to torrc
and restarting tor. Seconds later
/some/place/hidden_qemu/ will contain a file
hostname with the .onion address
tied to the SSH port of the emulated system. The
emulated system is now reachable by SSH only.
Connections to the system will be shown to originate at
10.0.2.2.
Assuming that qemu makes no errors (ahem), accounts
on the emulated system can not easily find out where the hosting
machine is (for small values of "not easily").
The Bank for International Settlements (BIS) hosts
an annual conference that brings together central bank governors, leading academics
and former public officials to exchange views.
At the 13th Annual Conference a research paper was presented by Bengt Holmstrom of the MIT titled Understanding the role of debt in the financial system on the mechanisms
of the financial market in connection with
the 2007-now crash.
The paper includes the following fascinating statements:
[..] But it is hard to believe that investment bankers would be colluding to defraud investors
[by issuing opaque securities].
Probably as hard to believe as that investment bankers would be colluding to defraud investors by
manipulating the London interbank offered rate (they did). Or by manipulating foreign exchange rates (they did). Or by manipulating the ISDAfix Interest Rate Derivative Index (they
did).
Or that a publicly held, international corporation would massively invest in
the expansion of the Auschwitz concentration camp (they did) .
An economic reality is that white-collar crime has a higher Return on Investment than most legal activities,
so the imperative of increasing profits enforces criminal behaviour,
specially when the the rate of detection+prosecution+conviction is near zero.
And shortly after:
[..] But it equally hard to believe that hard-nosed profit-hungry investment bankers and
traders would be ignorant out of ignorance.
The crash did not harm the profits of aforementioned bankers and
traders at all. So there is no incentive to smarten up (Holmstrom is supposed to be an
expert on incentives).
Later we read:
Invoking the empirical sucess of the EMH [Efficient Market Hypothesis] (in a variant they
call relative EMH), Gilson and Kraakman (2014) among others have advocated [...]
What the crash of 2007 very empirically proved was the failure of the Efficient Market Hypothesis.
If prices reflect all available information, and still fluctuate by more than 50 percent
in a single day, then that reflecting property is worthless.
That leading academics show such naïvité at the motivations
of criminals and cling to unrealistic assumptions is just depressing.
The paper goes on to show that collateral-backed debt is an extremely stable investment,
and information-insensitive (because 1. it is backed and 2. the debtor might recover before
the debt contract ends). Having more transparent collateralisation, Holstrom argues,
would affect the traders' belief system as to the value of the lending bank, thereby
endangering the stability of banks, which is posited as a common good. In other words:
market participants are not rational, they have “belief systems”
market efficiency is bad for market participants
market efficiency is not a necessity, it can easily be avoided by publishing less information
This reasoning could be called anti-circular, and I'd suspect that there is no
other field of academics where conclusions negate the premises used to draw the conclusions.
Ernst-Ludwig von Thadden's attached commentary at the end of the paper shows some hope, as
he points out the aspect of time (mostly ignored by economists, because differential
equations are just too hard) in the handling of debt, i.e., debt based vehicles rely
on a rollover of short-term debt over time. So they're not so risk-free over a longer term.
Gödel proved
Über formal unentscheidbare Sätze der Principia Mathematica und verwandter Systeme
the incompleteness of minimal logic combined with
minimal arithmetic. He was careful to point out that every step
in the proof is constructive. So one would assume that the whole
process up to the unprovable theorem about numbers could be implemented.
The original paper in fact has a point by point implementation in
Gödels's own notation of primitive recursion. Porting this to
Scheme seemed viable.
Gödel has a curious programming style, specially when it
comes to performance. For example, after definition of Pr(n)
as the n-th prime number, l(n) as the number of encoded numbers in
n, and n Gl x as the n-th coded number
in the number x, he defines the concatenation of terms x and y as
x * y =
ε z { z ≤ [Pr((l(x)+l(y)))]x+y &
(n) [n≤l(x) → n Gl z = n Gl x ] &
(n) [0 < n ≤ l(y) → (n+l(x)) Gl z = n Gl y ]}
which translates as :
To get the concatenation of x and y, find the first number z, starting from 1, such that z is smaller than the
len(x) + len(y)-th prime taken to the (x+y)-th power, and such that for all n less than len(x)
the n-th term in z is the n-th term in x, and such that for all n less than len(y),
the (n+len(x))-th term in z is the n-th term in y
Remember that the n-th encoded term k in x is the factor (n-th prime)k of x, so
this algorithm will try an incredible number of wrong candidates before reaching a likely candidate.
While implementing Gödel's proof in a kind of Test Driven Development I had to
stop at point 22 in the original paper, because from that point on even trivial tests will not
finish before the sun burns out. For an explanation, see
end of
code.
As everybody but the worst conspiracy theorist knows, everything sent over
the Internet is recorded and can be used against us (the buzzing noise you're
hearing is an armed drone circling the building).
Encrypting e.g. Internet Relay Chat a la PGP would protect the message on
the wire from eavesdropping. But if the message is recorded (which it is),
then a compromise of the involved secret keys would allow decryption at
a later date. And since thorough inspection of laptops at airports is routine,
we can assume that keys do get compromised now and then. With classical
public key crypto, the potentially incriminating content is also digitally signed,
so it can be used as a strong evidence against the utterer.
Can we make conversations on the Internet more like private conversations,
which are not normally recorded and where utterances are not signed?
This was answered to the affirmative in Borisov, Goldberg and Brewer's
paper Off-the-Record Communication.
And there's an implementation.
A working constellation for OTR conversation on IRC consists of
a pure Python implementation of OTR in the module python-potr
There are serious interoperability problems between various implementations.
What seems to verk is
weechat
version 1.0.1
python-otr (potr)
version 1.0.1 (the VERSION in the __init__.py says (1,0,0, 'final')
whereas the version in setup.py says '1.0.1')
weechat-otr
version 1.5.0
With the /otr policy:
allow_v2 (allow OTR protocol version 2) : on
html_escape (escape HTML special characters in outbound messages) : off
html_filter (filter HTML in incoming messages) : on
log (enable logging of OTR conversations) : on
require_encryption (refuse to send unencrypted messages) : on
send_tag (advertise your OTR capability using the whitespace tag) : on
Peter Welch's Essay
movingly reports how it is to be a sysadm and/or programmer in our networked
and hype-driven world of defective software. I read it aloud to my significant
other because it is so true.
The simple terminal by the
laudable suckless.org persons lacks xterm's
Tektronix 4014 emulation and several other features of questionable
utility.
The engineers' war cry "Keep it simple, idiots" is more audible
in st's implementation, less than 4 kLOC, and
anti-aliased fonts all the same (by use of libfontconfig).
At a talk given at the TU Munich, somebody asked Jacob Appelbaum why he (the questioning party)
should care about privacy at all. I routinely ticked off a list of possible answers, but
Jacob had a new one (to me): (quoted from memory)
So you're doing nothing illegal, why should you worry about privacy?
Well, in the
late 40ies there were people who were thinking about the possibility of changing
the political landscape of the US. They visited lectures, read papers and pamphlets etc,
everything totally legal. Yet a few years later they were accused of being communists
and were fired. Because they did something totally acceptable a few years earlier.
In the 90ies there were Muslim families in the US who followed the custom of donating
to foreign aid organisations. A few years later those organisations were decreed to
be aiding terrorists and therefore everybody giving them money in the past is now
a criminal. Because they did something totally acceptable a few years earlier.
And who knows what totally acceptable deed now will be illegal post hoc tomorrow.
The accumulated history of past behaviour can be used anytime in the future to
discredit or accuse. And the accusing party can filter the data for damning evidence,
whereas the accused has no access to the data to find exonerating evidence in it.
So history teaches us that everybody should have very strong objections against
a secret store of every word they ever muttered online.
In Germany, it is a felony to be member of a criminal organisation. That an
existing organisation has criminal purposes can only be decided after somebody
joined it. So this definition of a criminal act by being a member of some organisation
implies the post hoc for at least some members.
What does it do? It returns a function that returns 1, 2, 3, ... when
called repeatedly. It's a way of keeping state in a world of functions.
Don't confuse it with C's static Variables inside functions.
mkcounter constructs a new counter object for each invocation,
so
def mkcounter():
n = 0
def _inner_():
n = n+1
return n
return _inner_
c1=mkcounter()
print c1()
fails with UnboundLocalError: local variable 'n' referenced before assignment,
which is somewhat confusing, since n is visible in _inner_ if
the n = n+1 line is removed.
The impossibility of LoL in Python has been pointed out in
PEP-3104 but was only fixed in Python 3.
In Python 3 it's possible to reconstruct LoL by the dubiously named nonlocal
directive:
def mkcounter():
n = 0
def _inner_():
nonlocal n
n = n + 1
return n
return _inner_
c1=mkcounter()
print(c1())
The local Fablab has a laser cutter. What would
be more natural than to use it to produce jigsaw puzzles? The snag is: How
get the patterns to saw as SVG graphics. The Answer: create an archetypical
interlocking border of a jigsaw puzzle piece as SVG path and randomly transform
it for every connection in a n×m grid. Implemented
in Chicken Scheme.
emacs has the fabulous SLIME mode which
turns emacs into a LISPmachine, with interactive inspection and whatnot. It talks over TCP to
a LISP REPL wrapped in SWANK, executing a huge palette of commands to debug and trace code,
as well as the more-or-less trivial evaluation of code snippet from emacs buffers.
As a very weak approximation in vim there's jpalardy's vim-slime which uses screen to paste
stuff from vim into a screen window presumably running a REPL. The implementation
is totally vim specific.
If the action is just to paste stuff into another window using screen's own -X
option then it should be doable with a shellscript. So here are swan and
slim.
swan
starts the Chicken Scheme REPL and
injects the window's identifier into screen's environment.
slim
pastes its stdin into the REPL window.
Combined with good-old vi's map keybinding command
this is just as powerful as vim-slime but more flexible.
My .exrc now contains the line
:map C !%slim^M
which pastes text between matching parens into the REPL.
Update
slim now uses screen's register s so that the copy/paste
register remains untouched.
Started to play with Plan9 again.
First major experiment: Run a bare-metal cpu server without local disks. All configuration
can be done from an OpenBSD server supplying the loader, kernel, bootup-config, and filesystem.
The Plan9 server runs on an old 1U Pentium 4 server.
Results so far: PXE finds Plan9 loader, that again loads a plan9.ini by TFTP
which specifies a kernel, which then mounts its rootfs from a u9fs on
OpenBSD. Said rootfs contains cpurc which determines the server's behaviour.
Once the PXE Plan9 bootloader
9pxeload is running it pulls the file /cfg/pxe/001122334455 from
the DHCP/TFTP server. This file is used as the plan9.ini.
9pxeload will load 9pccpu from the TFTP server it
found on ether0 and supply that kernel with the infomation that
its rootfs will be remotely supplied from 192.168.66.11.
Console is on first serial interface with 19200bps and no parity.
On 192.168.66.11 the following entry in inetd.conf
starts 9legacy's modified
u9fs
process on demand:
9fs stream tcp nowait root /mnt/9atom/unix/u9fs u9fs -a none /mnt/9atom
(This implies that the service 9fs is already defined as 567
in /etc/services.)
The u9fs exports
The original u9fs found in
/sys/src/cmd/unix/u9fs.c exported the whole fs of the server.
This led to the custom of chrooting the process, with all the
pitfalls included.
The 9legacy patch
allows to export arbitrary subtrees.
the filetree under /mnt/9atom without
authorization. This is excusable only in a private network and necessary only
because my rootless cpu server does not know the password for the remote fs.
A way around that would be to put the password into the kernel itself (which
again is totally insecure in an open network where everybody can fake the MAC
and pull the kernel...)
The Plan9 server can now be controlled completely from the OpenBSD machine
which is nice for testing configurations.
zbx_malloc2 is defined in src/libs/zbxcommon/misc.c: line 255 as:
void *zbx_malloc2(const char *filename, int line, void *old, size_t size)
{
int max_attempts;
void *ptr = NULL;
/* old pointer must be NULL */
if (NULL != old)
{
zabbix_log(LOG_LEVEL_CRIT, "[file:%s,line:%d] zbx_malloc: "
"allocating already allocated memory. "
"Please report this to Zabbix developers.",
filename, line);
/* exit if defined DEBUG, ignore otherwise */
zbx_dbg_assert(0);
}
for (
max_attempts = 10, size = MAX(size, 1);
0 < max_attempts && NULL == ptr;
ptr = malloc(size), max_attempts--
);
if (NULL != ptr)
return ptr;
zabbix_log(LOG_LEVEL_CRIT, "[file:%s,line:%d] zbx_malloc: out of memory."
"Requested " ZBX_FS_SIZE_T " bytes.",
filename, line, (zbx_fs_size_t)size);
exit(FAIL);
}
So where're the pearls in this?
the old parameter is forced to be NULL, so why pass it at all???
noticed the for loop? It tries to malloc ten times before giving up. This
seems to assume that some concurrently running part of zabbix frees memory, or that
the system suddenly (while this loop is running, that is) assigns a higher memory bound for zabbix.
noticed the MAX in the for loop? It tries to catch and disguise the error of requesting zero
bytes by always returning at least one byte
Three less known features of MatLab
allow for memoizing functions:
nested functions
property lists on Variables
function handles
Code:
function mf = memoize(f)
% Returns the memoized version of function f.
% f must have exactly one numerical argument.
% The memoized version cannot be called without an argument.
% Memoizing functions of continous ranges
% may not be as useful as imagined...
h = []; % our pseudo hashtable by abuse of the property list.
% MatLab creates this fresh for every call of memoize
% and retains it for the lifetime of the memoized function
function r = ff(x)
% matlab allows only "MatLab words" as keys
xstr= ['m', num2str(x)];
if isfield(h, xstr)
r=h.(xstr);
else
h.(xstr) = f(x);
r = h.(xstr);
end
end
mf = @ff;
end
Everybody has seen various travesties of Claude Garamond's typeface because
it is one of the favourite fonts for books. Georg Duffner (with the help of
many) has created an
OpenType Font from an scan of a 1592 cut of Garamond's roman font.
A notable difference to modern cuts is the height of the stems of lowercase letters.
This seems to be a trend, even new typefaces like the original Times Roman look
flattend in newer cuts.
Recently I stumbled over Steve Yegge's essay “Execution in the Kingdom of Nouns ”
which reflects on the linguistic styles of programming philosophies. Really something to
think about. The points stated in the essay are quite observable in code that comes my way.
One nicely wrought wreath from the many flowers out of the Garden of Object Oriented
Design Patterns is the following:
For the lack of a nail,
throw new HorseshoeNailNotFoundException("no nails!");
For the lack of a horseshoe,
EquestrianDoctor.getLocalInstance().getHorseDispatcher().shoot();
For the lack of a horse,
RidersGuild.getRiderNotificationSubscriberList().getBroadcaster().run(
new BroadcastMessage(StableFactory.getNullHorseInstance()));
For the lack of a rider,
MessageDeliverySubsystem.getLogger().logDeliveryFailure(
MessageFactory.getAbstractMessageInstance(
new MessageMedium(MessageType.VERBAL),
new MessageTransport(MessageTransportType.MOUNTED_RIDER),
new MessageSessionDestination(BattleManager.getRoutingInfo(
BattleLocation.NEAREST))),
MessageFailureReasonCode.UNKNOWN_RIDER_FAILURE);
For the lack of a message,
((BattleNotificationSender)
BattleResourceMediator.getMediatorInstance().getResource(
BattleParticipant.PROXY_PARTICIPANT,
BattleResource.BATTLE_NOTIFICATION_SENDER)).sendNotification(
((BattleNotificationBuilder)
(BattleResourceMediator.getMediatorInstance().getResource(
BattleOrganizer.getBattleParticipant(Battle.Participant.GOOD_GUYS),
BattleResource.BATTLE_NOTIFICATION_BUILDER))).buildNotification(
BattleOrganizer.getBattleState(BattleResult.BATTLE_LOST),
BattleManager.getChainOfCommand().getCommandChainNotifier()));
For the lack of a battle,
try {
synchronized(BattleInformationRouterLock.getLockInstance()) {
BattleInformationRouterLock.getLockInstance().wait();
}
} catch (InterruptedException ix) {
if (BattleSessionManager.getBattleStatus(
BattleResource.getLocalizedBattleResource(Locale.getDefault()),
BattleContext.createContext(
Kingdom.getMasterBattleCoordinatorInstance(
new TweedleBeetlePuddlePaddleBattle()).populate(
RegionManager.getArmpitProvince(Armpit.LEFTMOST)))) ==
BattleStatus.LOST) {
if (LOGGER.isLoggable(Level.TOTALLY_SCREWED)) {
LOGGER.logScrewage(BattleLogger.createBattleLogMessage(
BattleStatusFormatter.format(BattleStatus.LOST_WAR,
Locale.getDefault())));
}
}
}
For the lack of a war,
new ServiceExecutionJoinPoint(
DistributedQueryAnalyzer.forwardQueryResult(
NotificationSchemaManager.getAbstractSchemaMapper(
new PublishSubscribeNotificationSchema()).getSchemaProxy().
executePublishSubscribeQueryPlan(
NotificationSchema.ALERT,
new NotificationSchemaPriority(SchemaPriority.MAX_PRIORITY),
new PublisherMessage(MessageFactory.getAbstractMessage(
MessageType.WRITTEN,
new MessageTransport(MessageTransportType.WOUNDED_SURVIVOR),
new MessageSessionDestination(
DestinationManager.getNullDestinationForQueryPlan()))),
DistributedWarMachine.getPartyRoleManager().getRegisteredParties(
PartyRoleManager.PARTY_KING ||
PartyRoleManager.PARTY_GENERAL ||
PartyRoleManager.PARTY_AMBASSADOR)).getQueryResult(),
PriorityMessageDispatcher.getPriorityDispatchInstance())).
waitForService();
Inspired by Adi Shamir's TWINKLE optical
device for finding smooth numbers, which works at GHz, I wrote an audio device for finding smooth
numbers, which works at low kHz. In absence of a good, screeching acronym, I'd call it
Dysphony in b-Smooth.
The idea is to convert the smaller prime factors of numbers into sound. The code does this
by keeping n counters, each of which is increased modulo its individual prime.
At the moment, these are the first 1000 primes. After every increment the counters
that contain a zero are collected and a sine wave is constructed from the associated
frequencies (index*(2000/n) + 40 Hz) at an amplitude proportional to
the logarithm of the prime (so that the frequent divisors 2,3,5,etc have a low impact).
Each sound lasts a small fraction of a second. If a loud noise is audible, it is
the representation of a number with many different and/or larger prime factors.
The scientific value of this is approaching zero from the left, but it was a nice
exercise to have the computer produce sound after my last attempts in 1987 on
an Atari ST.
For eight years it has been known (and Verified)
that MySQL does not release diskspace it has claimed in its ibdatax files.
The bug leads to full disks and database outages since the only way arround it is to shut down
the DB, dump it (consuming even more space) scrubbing the disk and restoring from dump.
In the good old days, when NTK was still around,
I always envied the British for their absolutely superior hacker conferences.
To give an example, a talk by James Larsson on NotCon'04 explains how
to measure time with a BBC Micro and a
Marks&Spencer Prawn Sandwich. It's in the first ten minutes
of this stream
(local copy).
Since NIS has seen its hayday (in the early 90ies), we switched to the highly
secure LDAP+Kerberos setup. OpenLDAP is touted as the allround “Solution”
to all user account management, sorry, I meant to say account provisioning.
After converting our NIS passwd file to thousands of LDIF files we
imported them with the obvious three-liner
for i in *ldif; do \
ldapadd -v -W -D "cn=admin,dc=our,dc=domain" \
-c -H ldapi:/// -f $i
done
After fiddling with half a dozen files in /etc, the client systems
could look up user data on the LDAP server. Our test for that was
and install that as a list of valid recipients of e-mails.
This was a grave error, because one of the manymany default settings of OpenLDAP
is to return only the first 500 answers to any request. So the list was short
by a few hundred accounts.
Considering that LDAP has no concept of a cursor and one cannot ask for the next 500
entries, one can only ask
OpenBSD's installation ramdisk does not contain useful tools
to quickly transfer files from a remote machine. Specially
the absence of netcat is painfully felt.
The typical routine to transfer a set of files from Host A to the
Host-to-be-installed B would normally be
A% tar cf - dir1 dir2 | nc -l 1234
B% nc hostA 1234 | tar xpf -
The following creates a tar file that
writes stuff (/etc/yourpasswd in this
case) outside the directory
where it is extracted:
touch foo.c bar.c Makefile
ln -s /etc info # tar can do symbolic links
tar cf src.tar *.c Makefile info
rm info
mkdir info
touch info/yourpasswd # where does this extract?
tar rf src.tar info/yourpasswd # tar can extend archives
gzip -9 src.tar
This of course only works when tar zxf is run as root,
but that is not unheard of, right?
Few people but nameserver admins know the .arpa
toplevel domain.
It has an hierarchical scheme with zones just as all other TLDs.
It's main use is to reverse map addresses. For an IP
address like
111.22.3.4
this is done by
requesting the PTR record for the hostname
4.3.22.111.in-addr.arpa
The DNS server for
in-addr.arpa delegates the request to
the server responsible for 111.in-addr.arpa
and so recursively until a server is found who is responsible
for the whole network containing the address. The reply
typically is a hostname.
For IPv6 the domain is ip6.arpa and the
encoding for e.g.
But there is no technical barrier against requesting other record
types from under the .arpa tree. The DNS servers happily
return A,
AAAA,
CNAME,
DNAME or other records when asked nicely.
And nothing prevents an DNS admin from placing non-PTR records
in the .arpa subzone. And nothing prevents
them from prefixing arbitrary strings in front of the IPv6 subnet.
And of course those .arpa names can be used
just like hostnames...
For example, a valid URL for this blog could be this or
that or even
thiß.
Perhaps URL-based filtering can be subverted this way.
postfix compiles on OpenSolaris
postfix runs
postfix tries to accept email
postfix uses statvfs to enquire free space on /var/spool /var/spool is on ZFS with > 2TB free space statvfs dies (EOVERFLOW)
postfix dies
poor email
UPDATE: small patch fixes this, assuming
that an FS with more than ULONG_MAX/2 free blocks has
— for all purposes of postfix — exactlyULONG_MAX/2 free
blocks.
Miod Vallat ported OpenBSD to the chinese MIPS64
remake Loongson 2F,
so I wiped the bloated Linux installation
from my Yeeloong.
On the Pros side, OpenBSD on Loongson works out of the install,
with X11 and everything running.
On the Cons side, there seems to be a serious flaw in
fundamental stuff that stops
Python from building and introduces bugs in libgmp.
And without Python no mercurial
and therefore no happiness yet. UPDATE: The python build issue is fixed in -current. Mercurial works
on the yeeloong!
All creativity is an extended form of a joke. Most
creativity is a transition from one context into
another where things are more surprising. There's an
element of surprise, and especially in science, there
is often laughter that goes along with the
”Aha“. Art also has this element. Our job
is to remind us that there are more contexts than the
one that we're in --- the one that we think is reality.
The Curta is a mechanical computing device, about
12.5 cm high, 8 cm in diameter, with
49 bits internal precision. I'm totally in
awe about the elegance of the design and the smooth
handling. Trying to actually compute something, e.g. a
square root, on this machine, immediately makes one
aware of the roots (sic!) of numerical mathematics. There
simply is no button marked √ on the Curta, and
still people used this very machine to compute square
roots (and logs, and trigonometric functions, ...).
Until the 1980ies most scientists knew how to
efficiently compute everything on such add/substract machines,
and this knowledge is now buried without a tombstone.
Russ Cox's drawterm
is a terminal program to connect to a Plan9 CPU server from Unix. This
is a port for OpenBSD (i386, amd64, sgi and sparc64).
Plan9 normally provides a graphical user interface
instead of just a Command Line Interface on login, and so
does drawterm. In Plan9 terms, it exports
a part of the Unix box's drawing device, the keyboard and
the mouse to the CPU server and the programs started there
more or less directly draw on the window. No need for X-Forwardings
and the like. In addition it exports the user's $home directory to the
CPU server as /mnt/term, so that the usual routine of
XSLT relates
to general purpose programming as Cholera relates to dinner invitations.
Variables in XSLT aren't, and there's no imperative iterative statement,
so state must be kept on stack and recursion is the only way of iteration.
Combined with the fact that most XSLT compilers that we tried do not
utilize tail recursion, this quickly leads to stack overflows even
for small inputs.
Thanks to Meredith L. Patterson
for cool tricks to save space on stacks
Typing is non-existant, strings are cast to integers, whole XML subtrees
to strings and so on.
The XPath
query language can be used to select elements or subtrees of XML documents.
Subtrees resulting from such selections can be assigned to variables
and passed as such to functions (templates in XSLT-speak)
but their elements cannot be accessed by XPath any more.
Although XSLT abhors brakets, ampersands and double quotes,
it is possible to clobber together arbitrary strings. But
it not possible to output them in HTML format contexts,
so it is necessary to hark back to hacks including iframes
with data: url hrefs.
The ironically named Chinese company Lemote
has produced Linux-based set-top boxes for some time.
What makes these and subsequent Lemote boxes unique is that they run
on MIPS64 CPUs.
Most commonly associated with MIPS are the legendary Silicon Graphics Workstations
of the 90s. But since then, MIPS-based boards have been used in many
consumer devices, e.g. most Linksys wireless routers, Cisco routers,
Playstations,
The CPU in Lemote's newer products is basically a MIPS R4700, called Godson or
Loongson-2E, with bigger cache and larger TLB.
What brought us to Lemote hardware was the
announcement of a completely
open-sourced netbook. From the boot monitor (a modified
PMON) to the desktop, everything was supposed to be open and modifiable.
The process of ordering hardware from Lemote turned out to be surprisingly simple.
After exchange of a few E-mails and an international money transfer,
we got six laptops with 1Gb RAM, 160 Gb disks,
American keyboards and an English Debian installation. Price after customs,
including shipping, was about 320 Euros per machine.
Jun Rekimoto's Time-Machine Computing
is a neat idea for representing large (probably not huge) amounts of personal
documents/images/other data in their chronological context.
It assumes that people have no problem remembering their actions
if given hints to what other actions they performed around the same time.
So instead of organising saved/created files by a rigorous
system of hierarchical sub-directories and names, one would
use on the creation or modification times and the good old neural network.
Rekimoto developed a Java-based desktop environment based on this idea.
A more practical approach IMHO would be to enhance one the many open source
file managers by a slide bar that allows to scroll backwards in time through
the directory. I.e. when activated, the position of the knob presents a
point in the past, the leftmost position representing the creation of
the oldest file in the displayed directories. At each position, the
only files shown would be the ones created at or around the date
represented by the position. All other files should be faded from view.
Another way of implementing a time view would be to center on a
selected, presumably well-remembered file and fade out all others,
the shading depending on the chronological distance from the selected
file. I.e. when you click on a file, you would clearly see the files
that you created shorly before/after the selected one, with earlier/later
one fading out progressively.
And again there's 24 bottles of beer waiting for the brave implementor …
The terms file server, file system and the abbreviation fs
appear a lot in Plan9 documentation. For example, there are the manpages
fs(3), fs(4), fs(8), and kfs(4).
First fs(4) aka Ken's FS. This was a file server
inside the kernel which required a specially built kernel and
was used together with a dedicated CPU server and
many terminals. It is not part of the kernel sources any more,
but its manpage lives on. To add confusion, there is also a
manpage fs(8)
for the console of Ken's fs.
Then there is kfs(4),
a file system for terminals.
It is implemented in user-space. No relation to Ken's FS besides the name.
Strangely there seems to be no option to repair
a broken kfs:
If the file system is inconsistent, the user is asked for permission to ream (q.v.) the disk.
(reaming means deleting).
kfs cannot be managed by a console like Ken's fs and
fossil, but
by options to an executable kfscmd.
UPDATEkfscmd has commands to repair a broken kfs.
As another example for the non-injectivity of abbreviations, there's
fs(3)
which is not a file system at all, but a kind of soft-raid that allows concatenation,
striping and (simple) mirroring of files, e.g. disks.
On the fourth hand, there is
fossil.
This is the current default for CPU and File servers. It can be configured to
move its blocks to an archival storage server
venti.
It is managed with its own console
fossilcons
which attaches itself not as /srv/fossilcons but
/srv/fscons.
I offer 12 Liters of
top-quality Franconian beer
(Leutenbacher Drummer-Bräu) for fixes of each of the following:
plan9ports: provide a libthread for OpenBSD-amd64.
OpenBSD: vi: make 'vi -r' work after a power failure.
OpenBSD: i386: make SMP work on IBM ThinkPad X60. UPDATE works now as of 4.2-stable
OpenBSD: Software Suspend ala swsusp to get around all that
silly ACPI stuff.
OpenBSD: AMD64: Enable a MAXDSIZE of greater than 1 Gb.
UPDATE it's now 8 Gb in OpenBSD 4.4-beta
OpenBSD: VAX: ELF with dynamically loadable objects.
OpenBSD: all: port Ai's setmacaddr patch
to 3.6. UPDATE The 12 l for this
have been (successfully) claimed by Christian Kellermann with his
patch to current.
UPDATE The OpenBSD team added the feature to the
source (by a different patch, prs 2117 and
2118).
libGMP: Support AMD64 with true 64bit arithmetics.
GnuPG: all hash implementations in cipher/
have a function {md,md5,rmd160,sha1,sha256,sha512}_write.
The implementation
is quite obfuscated with a totally unnecessary level of
recursion with several terminating conditions. Replace
these _write functions
by something more readable. UPDATE The terrible code is
by Ulrich Drepper, not gnupg's author Werner Koch.
GnuPG: add functionality for signing arbitrary PKTs, thus
allowing signatures on signatures.
libnet: functions for construction of arbitrary chains
of all possible IPv6 headers.
Just sent the first few thousand packets over an IPv6-only
PPPoE uplink provided by rh-tec.
Config on OpenBSD with bge0 as the physical interface
connected to the DSL modem:
ifconfig pppoe0 pppoedev bge0 authproto pap peerproto pap \
authname 'thename' authkey 'secret' up
After a few seconds, pppoe0 receives a Router Advertisement and
gets it's prefix. The rest is plain sailing (ssh -6 and so on).
Answer: all of them are equally likely outcomes of 23 coin-flips.
Sérgio B. Volchan tells the history of the concept
of randomness in mathematics
in an article
for the American Mathematical Monthly.
It is quite fascinating IMHO how seemingly resonable definitions
of randomness were put forward and shot down later to be replaced
with the next definition. The most recent definitions preclude
meaningful checks for randomness by examining finite parts of
a sequence, so the conundrum remains: Is 7 a random number?
The Jupiter ACE
was a home computer produced in the UK in the 80ies.
It had a FORTH interpreter instead the usual BASIC of the C64, BBC micro, etc.
Their Manual explains
the inner workings of the machine in an accessable way. Compare that
to the thousands of VBA books that keep the reader totally in the
dark what goes on behind the funny icons.
Spamfilters add complexity, which in turn makes v6 transition harder.
Setup:
Host A (running OpenBSD) has dual stack v4/v6 with routable v4 address
Host B (running Plan9) has dual stack v4/v6 with a subnet-local v4 address
Both machines have a routeable v6 address and run an MTA.
So I assumed that it should be possible to send mail from A to B.
Turns out to be not that simple. The Plan9's MTA uses various heuristics
to find out if incoming mail is spam (as do other MTAs). One of the checks is to connect
to the MTA listed in the MX record for the sender's address' domain.
Host A's MX record is v4-only, so B cannot connect to the
MTA, so it rejects the mail. Not only the sender and the receiver have
to be v6-enabled, but also the sender's MX (and probably the blacklist
providers, etc).
Plan9 is an operating
system by the authors of the original Unix, with integrated
support for distributed applications.
Plan9 has its own windowing system, rio, quite different from
X11.
It is possible to connect to Plan9 machines
by drawterm
from Unix machines running X11. drawterm
starts the windowing system on the remote Plan9 and
everything works as if sitting in front of it.
While typing from one machine I remembered I had
already solved a problem in a one-liner,
but on a different drawterm which ran on a Unix box miles away.
So the other drawterm runs the rio mounted on
/srv/rio.myname.5678. To get at the scrollback
of a window displayed on a screen on a totally different machine:
cpu% mount /srv/rio.myname.5678 /n/wsys 1
cpu% cat /n/wsys/text
[...lines of output...]
[...including the one-liner...]
RSA + OAEP + RC4 = PSP
PGP on the cheap, implemented in a bunch of shell scripts.
All crypto in dc(1), nice redirects in/from
FIFOs. Download the files (.tar.gz) now!
(Tested on OpenBSD, GNU sed manpage:
“POSIX.2 BREs SHOULD be supported”
But they aren't) UPDATE Pull the sources again, fixed some bugs. Thanks
to Michael Gernoth.
With a shell account on an arbitrary POSIX semi-compliant system, one should
have access to a Bourne-like Shell, awk, dc,
sed and companions. Given a source of randomness this should
be sufficient to code RSA + a symmetric cipher, kind of extremely poor man's
PGP.
I had some problems finding ways to output binary stuff from ksh.
UPDATE: New version seems to work with bash.
On Intel at 1.6 Ghz it encrypts/decrypts at 184 Bytes per second.
One optimization could be to put the keystream generation entirely in a dc script,
start that in a sub-process, and read single bytes from a fifo.
UPDATE: New version does this, 370 Bytes/sec now.
Key creation time and sigs from forgotten keys influences the ranking
All norms on key graphs have to deal with time somehow. This
is because keys are created over time, revoked, they expire, their passphrases
are forgotten … Signatures expire, point to revoked keys …
In the BC norm, this has a side-effect on newer keys:
since newer keys will never get signatures from revoked or unused
keys, they are at a serious disadvantage (sorry, weasel :-)).
If there are n keys in the component, and only one has
a link to/from an old key, then it's BC will increase by n-2
(because n-2 shortest paths lead through it to the forgotten
key).
At the moment I see no way of repairing this.
mmap(2) maps a file to a range of memory and gives
the calling process a void* to manipulate the contents
of the file. If no file descriptor is given, it creates an
“anonymous” memory range. In both cases, the memory range
can be used for inter-process communication.
As an additional feature, the caller can specify how child processes
see the memory. If MAP_INHERIT is set, the children
see the same as the parent. If additionally (or more precisely OR-ally)
MAP_PRIVATE is set, modifications (i.e. writes) by the parent are
invisible to the children. If MAP_SHARE is set, the
children see the bytes written by the parent. The minherit(2)
syscall allows setting these bits for arbitrary pages.
Now, what would be the most stressing situation for the kernel?
Overlapping memory ranges with different copy/share policies for
several generations of processes. This program does exactly that.
It subdivides the same piece of memory recursively, and each child
sets another inheritance policy on top of the set ones of the stack
of parents.
-f <file> use <file> to mmap on
-m <size> size of mmaped area in bytes
-r <level> the number of recursions
-n <num> number of byteblocks to touch in each incarnation
TODO: let each child mmap the same file to another location,
with different policies…
It is hard to confine untrusted software to just the stuff it is
supposed to do. Server processes can be run as unprivileged users,
chrooted or jailed in their own namespaces. If the software has to
display something on the user's X11 however, different measures
have to be taken.
One approach is to run the program under surveillance of
systrace. This is good, but the code must have access
to the X server and could try to grab/inject XEvents.
The following script (download)
opens a nested X server (Xnest)
and starts an xterm on it, running as another user.
Starting from there, the user at the display can start a window
manager and the suspicious software itself.
The programs inside the nested X cannot access the surrounding
X display. With restrictive file permission on the regular
user's homedir and standard precautions about the other
user's account, this could protect against a few attacks.
#!/bin/sh
#
# xsandbox username
#
# Start a nested XServer on display :1 and
# start processes in that Server as
# another user. Aim is to avoid grabbing
# of XEvents by untrusted programs which
# can be restricted to the nested display
#
# Requires sudo
function die {
echo $1
exit 1
}
user=$1
devrandom=/dev/arandom # Replace with your favourite PRNG if necessary
if [ -z $user ]; then
die "Please give a username"
fi
umask 0022
# Make two xauthority files, one for the user starting
# the script, the other as $user who will run inside the
# display.
xauth_you=`mktemp "/tmp/xauth.you.XXX"` || die "could not mktemp"
xauth_other=`sudo -u $user mktemp "/tmp/xauth.$user.XXX"` || \
die "could not mktemp as $user"
x1=`dd if=$devrandom bs=32 count=1 2>/dev/null | sha1`
x2=`dd if=$devrandom bs=32 count=1 2>/dev/null | sha1`
cookie=`echo $x1$x2|cut -c-64`
# Clean up when finished
trap 'rm -f $xauth_you; sudo -u $user rm -f $xauth_other' EXIT INT
# Create auth cookie for display :1.0
xauth -i -f $xauth_you add :1.0 . $cookie || \
die "could not create $xauth_you"
# Transfer authority to $user
xauth -i -f $xauth_you nextract - :1.0 | \
sudo -u $user xauth -f $xauth_other nmerge - || \
die "Could not transfer authorization to $user"
# Start Xnest
Xnest :1 -auth $xauth_you -sss 2>1 1> /dev/null & xnest_pid=$!
# Start xterm as $user inside the Xnest
sudo -u $user sh -lc "export XAUTHORITY=$xauth_other; \
/usr/X11R6/bin/xterm -display :1.0"
# Kill the Xnest when finished
kill $xnest_pid
Members of the security and safety community often claim
that software quality would improve if manufacturers would
be held liable for damages caused by their products.
The reasoning uses the negative incentive argument:
“If we produce faulty software, we will lose money.
Let's write correct software instead to increase shareholder
value.”
Let's examine this claim more closely:
A user experienced damage from a malfunctioning
program. How would she get compensation from the manufacturer?
Surely not by simply calling and announcing that a crash caused
X dollars of damage. Surely the vendor would claim that it
was a user error …. So user and vendor will end up in court.
The only proof of fault on the vendor side would be for the user to
recreate the state of her machine before the crash (how??)
reproduce the software error by taking actions explicitly mentioned in
the software's documentation.
Now suppose that there was a magical wand for taking snapshots of
computer states just before crashes. Or that the legal system
would permit claims on grounds of only the second part of the proof.
Then there would be a strong positive incentive to write software
that fails unreproducibly: “If our software's errors cannot
be demonstrated reliably in court, we will never lose money in
product liability cases.”
This introduces an interesting new paradigm of programming.
Methods of this school of programming could include:
Do something random
If an exception is raised which is not caused by
user input, look for a random function/method which can be called
in the current context and call that.
Procrastination
In multithreaded programs, if one thread runs into an error,
simply put this thread to sleep and hope nobody notices it.
Decoy
Produce fake virus scanner alerts, telling the user to e.g.
reboot imediately, thereby erasing the traces of the error.
Blame someone else
Inject errors in other running programs.
Example: A SEGFAULT handler looks for other programs from
different vendors running on the same machine when the error
occurs and forwards the signal to one of them. It then simply
waits. The user might attribute the freezing of the program
to the crash of the other.
Of course, really unreliable code needs randomness to select the action
to take. All modern operating systems now come with random
number generators which could be used for that purpose.
In machines with hardwire unique ids (UIDs), e.g. from the TPM,
there is the interesting (and rewarding) possibility to tie the
random behaviour to the hardware. This would allow
software vendors to sell horoscopes for computers!
the code walked against the direction of the links, silly me
pgpring cannot be relied on when parsing the keyserver dumps,
so we now pull the usernames from a keyserver, ugly
generate only the
top1000 by default. Longer rankings
are no problem, mail if you want them (or run the code yourself,
changing the parameter of top to some higher value first).
A prediction (which you can help to make self-fulfilling): we will find security holes in implementations of
protocol features which are
hardly ever used
not really understood
underspecified
Possible targets:
HTML & data: URLs
RFC 2397 defines
a URL type which carries its own content. This could play havoc with
HTML content filters, filtering proxies, and so-called "browser
security settings". Simply base64 the exploit and put it in
a <a href="data:base64...">. You can also
put iframes in data: URLs, which in turn …
recently. Very impressive, they defined a lot of really
incredible stuff. For example
the IPv6 Destination Options Header (RFC2460, Section 4.6)
is an optional header that allows to pad datagrams with zeros.
Glorio!
the IPv6 Routing Header (RFC2460, Section 4.6) defines
up to 127 hops through which a datagram should travel.
It specifies the hops by addresses, so that the header
alone can be up to 16 * 127 + 4 = 2036 bytes
long. The routing header may not be fragmented (RFC2460, Section 4.5),
and the minimum MTU is 1280 (RFC2460, Section 5). It makes the
mind boggle.
to compute the UDP body checksum, an IPv6 pseudo-header
has to be constructed in memory. The UDP checksum ignores the headers
between the address part and the UDP header, except when
there's a routing header present, in which case it has to
be parsed for the final hop, which will then be included
in the pseudo-header. Simple, fast, efficient.
While there are some compliance testing efforts, there seem
to be no checks about handling of non-compliant datagrams.
What happens if a datagram carries two routing headers,
three destination option headers, undefined NextHeader
values, or a Jumbogram header indicating a payload
of 4 Gigabyte on an ordinary ether interface?
Internationalization
Diverse pranks with Unicode are making the round (e.g.
shoestringfoundation's very own UTFbiffier), and the various
hacks to get wide-char support in standard applications,
and then there's Internationalized Domain Names
(RFC 3490)
and useful character encodings in X509 (for example Teletext
and T61Sting which includes really suprising chars,
see Peter Gutmann's highly readable X.509 style guide).
All that calls for further interesting exploits on the user interface.
ANSI terminal viruses (ok, it's viri, but tell that
to the walri)
We terribly ε¦ïʈè
ɦaϲќҽrႽ
tend to use command line interfaces on terminals, consoles,
xterms or even screen.
But there's been lots of interesting attacks involving
magic escape sequences.
A
recent paper by H.D. Moore points out that this is a pending
threat still.
URG flags and pointers
The TCP urgent feature implements the strange ITU-y idea
of sideband signaling. It basically tells the socket
that there's much more interesting data somewhere
later in the TCP stream. Practically no program uses this,
but who knows what shenanigans might be caused by an
URG pointer in a Jumboframe …
The sharing and co-operative commenting of bookmark-like links is
a very interesting idea. It takes the slashdot/scoop idea
to the extreme because everybody can dump what they find
interesting and sort other suggestions by keywords aka tags.
Popular implementations such as
del.icio.us or
CiteULike
are nice and well, but they are centralized, easy to flood
and a bit too open for my taste. So I was happy to
see that Ricardo Signes wrote
Rubric,
a free implementation of a del.icio.us work-alike, and
Steve Mallet at de.lirio.us
adapted the interface to make it look like del.icio.us.
I'm testing it right now and would like to run my own
tagged bookmark store, integrate part of them with this blog
and share the links with friends.
The Rubric code depends on loads of Perl modules and
it takes some few minutes to configure it. Ricardo
provides scripts to import existing link-lists quickly,
without going through the web interface. The input
format is a YAML
dump of a reference to an array of hashes with certain keys.
I wrote a little script
to convert Lynx's bookmarks
to that format. Stay tuned …
Update: the script
now works for "DOCTYPE NETSCAPE-Bookmark-file-1", i.e. Firefox,
Mozillas as well.
There have been a lot of ideas about how to allow
multi-writer web pages. The simplest implementation is the classic wiki
(everybody can write everything), the most useless
idea in this area is Annotea
which requires modifications at the client (as proof of
irrelevance, they implemented it for Amaya).
There are many applications where the ability to add
comments would be useful, and where the wiki concept allows
too much mischief.
A group of brazilians implemented what they call
co-links. This trickery of php/sql/javascript allows readers to
insert links in a text and add links to existing lists of links.
They require no modifications at the browser and the
new links are stored at the server (not always a pro, but a
good start when compared to annotea, where all modifications
are stored at the W3C), but not the content they point at.
A nice application would be, e.g. a distributedly annotated
edition of a literary text.
The specs for the highly esoteric
Dynamic Delegation Discovery System (DDDS), RFCs 3401 to 3405 all
contain the following curious phrase:
The entire series of
documents is specified in "Dynamic Delegation Discovery System (DDDS)
Part One: The Comprehensive DDDS" (RFC 3401) [1]. It is very
important to note that it is impossible to read and understand a
single document in that series without reading the related documents.
Since each document stating this is
itself a part of the series, recursion kicks in and it becomes
“impossible to read and understand” any of the RFCs.
This does not bode well for the rest of the standard.
The mean-minimum-distance of a key to all other keys
in the web-of-trust gives some idea of the connectedness
of the key. This is done in Drew Streib and Jason Harris'
keyanalyze.
But it does not express how the key
contributes to the infrastructure of the web-of-trust.
It would be nice to have measurement of, e.g.,
the number of otherwise disjoint communities which
are connected only or mainly through a key.
A quantity that expresses something like this is the
Betweenness Centrality. In a nutshell, it is the
number of shortest paths which lead through a vertex in
a graph. The paths are taken from every vertex, to
every vertex. If there is more than one shortest path
between two vertices, the centrality of the vertices on
the paths is increased only by the fraction of paths
which they are part of.
Formally, Betweenness Centrality of a vertex v is defined as
the sum of [(number of shortest paths from s to t
that go through v) divided by (number of shortest paths
from s to t)], where s and t
run over all pairwise different vertices ≠ v.
The code in Cwot.tar.gz
computes the betweenness centrality
of all keys of a graph. The graph must be presented in
the preprocess.keys format as in keyanalyze.
To compile the code, simply type 'make'. If your system
does not have /usr/include/sys/queue.h or
/usr/include/sys/tree.h you have to un-comment one line
in the Makefile, see there.
The algorithm used to compute the Betweenness
Centrality was taken from a paper by Ulrik Brandes,
“A Faster Algorithm for Betweenness Centrality”
in “Journal of Mathematical Sociology”, 25(5):163-177, 2001.
The time-complexity is O(nm), where n is the number of
vertices (keys) and m the number of edges (signatures).
The space-complexity is O(n + m), but my clumsy
implementation might scale worse.
My PGP key resides on one single machine, which runs no
services and is mostly offline. Mail is delivered to
another well-connected box. The mailbox format is Maildir.
To decrypt mails I need to transfer the stuff to the
machine with the key.
My .procmailrc on the connected box:
To sync the files to the secure box, I use
rsync.
The problem is that my mail reader renames the
files in the maildir to store flags like read,
replied, so rsync pulls too
many files. The following script helps:
tmpfile=`mktemp /tmp/mailsync.XXXXXXXX` || exit 1
for i in `find pgp -type f| sed -e 's/:[RSF,0-9]*$//'`; do
echo -n "new/" >> $tmpfile
basename $i >> $tmpfile
done
rsync -zvaubr --exclude-from=$tmpfile mailhost:~/Mail/pgp/ pgp/
rm $tmpfile
Naming and name spaces are important in a lot of contexts:
natural language (naming things, people, places, …)
programming languages (think about scoping, encapsulation, C's static, inheritance, …)
networking (Addresses, DNS, IDs for various types of sessions like in TCP or RPC, …)
crypto (Identifiers in certificates, fingerprints in PGP, …)
law (Trademarks, libels, …)
Unfortunately, computer science is mostly ignoring the whole topic.
In the hope to change this a little, I'm building a
bibliography/link list on naming.
Additions, corrections and comments are welcome!
The common technique for signing large amounts of keys
after a key-signing party is to, well, simply sign all
keys and mail them to their owners. But this might not
the best way. Because if you sign a key, you often
sign many uids with different e-mail addresses. If
any but one of these don't work you won't notice, because you
signed all of them and mailed the result around.
Thus your signature certifies that this key belongs
to addresses it doesn't really belong to.
To avoid this, Peter Palfrader
wrote caff. This Perl script
converts keys with many uids to many keys with just one
uid each, and signs these. It then encrypts each signed
key with itself and sends it to the e-mail address in
the uid. This helps to assure that you don't sign uids
with e-mail addresses which aren't under the control of
the signee. Caff removes other signatures from the keys
as well, to make the mails smaller and easier to process.
Peter Palfrader is the author of caff, I merely added a
few features to allow signing with multiple and older keys,
and to have caff just save the mails in a folder instead
of sending them off at once.
NEWS
Fixed an error in the handling of extensions (e.g. idea).
I carry around my old Vaio and connect it to
different subnets. Typing the same commands
(ifconfig ....; route delete default;
route add default ...; cp /etc/resolv.conf.place /etc/resolv.conf;
...)
every time I reconnected got boring, so the stuff
went into scripts. I later heard of Felix von Leitner's
divine.
It sends out fake ARP requests to divine to which
network the machine is connected, and takes configured
actions depending on the results.
It turns out
that it's pretty easy to re-implement this with
“standard&ddquo; utilities on OpenBSD. I use
arping by Thomas Habets from the ports-tree
and
ifstated supplied in the OpenBSD source tree.
ifstated is not installed in the standard
build process, but a simple cd /usr/src/usr.sbin/ifstated
make && make install
fixes that. The documentation for the config-file
ifstated.conf is non-existant, but an
example is in /usr/src/etc/ifstated.conf.
You can take my
minimal config
for multiple networks and adapt it by substituting
the name of your interface, the IP/MACs of the hosts
in your networks. Works fine in my setup.
While preparing a talk about extensions of
Merkle's hash trees, I found that it's extremely
complicated to draw nice binary trees with
WYSIWG software.
So I wrote code to do it.
It's in Perl and uses the GD module. GD's handling of
colors is awkward, but the code does it's magic.
Using the technique described in
another post, I now compute the betweenness centrality
of the strong connected component, using Jason Harris' pre-processed
keys as starting point. Results are at
http://pestilenz.org/~bauerm/wotstats.html
.
One problem with steganography is that the embedding of
hidden text in the covertext changes the statistical
characteristics of the covertext. With large amounts
of covertext, it becomes obvious. Niels Provos
addressed this in Outguess
by changing other bits in the covertext to minimize
the impact of the embedding on the chi-square test.
Would it be easier to embed undetectably if we can
generate the covertext ourselves. Definitely!
Mybal.pl does this. Supply
it with an ASCII text and it computes the
probabilities of characters following every sequence
of characters in the text. Supply it with a key,
a message to embed and a word, and it
will generate a covertext starting with that word.
The covertext has exactly the same probability
distribution as the orginal text, but the message
can be extracted from it, if the key is known.
How does it work? Mybal takes the word to start with,
interprets it as a sequence of chars and checks which
chars would be next in the sequence, and how probable
each of them are. It then throws a biased die (a PRNG
seeded with the key) to decide which char is next.
It appends that char and interprets the result as another
sequence and so on. If the list of possible next characters
contains two chars with the same probability and
the keyed random number generator chooses one of them
mybal looks for the next message bit to embed. If it's
a zero, then the randomly chosen char is appended.
If it's a one, the other equally likely char is appended.
This guarantees that the probability distribution is
always the same as in the orginal.
To extract the message, mybal starts with the first word
and walks along the covertext, always checking the list
of possible next chars. If the char in the covertext has
the same probability as another char in the list, then
a message bit could be embedded with that char. To check which
bit it was, mybal uses the keyed PRNG to generate the text
itself and thus sees which char it would have chosen on a
one or zero bit.
Assume that you have control over a zone somezone.net,
i.e. you can add records in that zone. With
this patch
to bind-9.1.3 you can designate a new domain, even a
TLD, e.g. .mytld. Every hostname h.mytld in that zone
is CNAMEd to a hostname j in somezone.net, where
j = SHA1(h . <secret>). <secret> is
set in bind's config file. This allows you to assign
arbitrary meaningful names in .mytld, like
icannsucks.mytld. The DNS queries that leave the subnet
with your modified bind refer to meaningless hostnames in
somezone.net. If you want to share this local namespace
with someone, you just have to send him/her the configfile entry
that defines the TLD and the secret.
At the Privacy Enhancing Technologies Workshop in 2004, Ben Laurie and
I did the following experiment: Take all RSA moduli from PGP keys presumably
created with old versions of PGP and compute the pairwise gcds
(Peter Palfrader supplied us with the keys). It turns out
that two keys of about 18.000 have a common divisor in their moduli:
pub 512R/A6A0B399 1994-08-22
uid Joe Schmuckley
and
pub 1024R/575F0491 1995-04-25
uid Ptolemy\x94XIV
I attacked the second key with Paul Zimmermann's Elliptic Curve Factoring implementation.
The key's modulus is
1549562663450840692268622483721103711669388864897522390528764 829445645828909290189247132280621825493873705019175480670501 2516682556124827129012380911158436701354213114871849305291083 202711859451406305095386470946490932290315424308032810615741 2235640682459755462203449571275078025946614196463838287264848 217233
This is not the product of two primes. So far we found the
following factors:
3 (Yes, three!)
3 (Yes, it's not even squarefree)
42742556573248957
314267779982277702367112491702024117309
The remainder is not prime but seems to contain no factors smaller
than 150 bits.
Fascinated by the Auralizer, I started my own, simplified
version, Netsound. The idea is to define
sound events to be triggered by network events. In netsound, you can
set pcap(3) filters together with bounds and the sound
to play if the event occured that often. E.g.:
filter: icmp and not src net 131.188
max: 10
soundfile: sounds/boing.au
You can define many of these events. Netsound uses libesd
to play and mix the sounds.
The Blum-Blum-Shub Pseudo Random Number Generator works basically as follows:
Setup
Generate two large primes such that they both equal 3 mod 4
Take the product N and forget the primes
Fetch an initial state x0 from a true RNG
Operation per step
compute next state: xi+1 = xi2 mod N
output the least significant bit of xi+1
Blum, Blum and Shub show that predicting the next bit from
the observed output is as hard as factoring N. In addition,
after erasing the primes computing previous states from the current one
is as hard as factorization. A problem exists with the
expected cycle length of the produced random bits. As
Terry Ritter pointed out, maximum cycles (near the size of N)
can be assured by choosing the primes as “double--Germain”,
i.e. p = p'*2 + 1, p' = p''*2 + 1, with p, p', p'' all prime.
My implementation generates
such primes. A possible application for BBS is generating
strong randomness on embedded devices without physical sources
of randomness. Upon initialization,
a truely random seed could be stored on the device, which later is
updated synchronously after each step of the algorithm.
Bored with being eleet on IRC? Why not take a look at
the forthcoming 32-bit eleetness brought to you by
Unicode(TM)(R)?
At the Shoestring Foundation Labs, where we invented
time machines long before H.G. Wells could think of one,
we are in the process of converting boring old ASCII
to totally eleet Unicode. See our example page!.
If you think you're really bored than guess how bored I was when I
wrote The Extended Euclidian Algorithm in a
one-line shell script.
Ok, it's a long line (160 chars in the
dc part), but it runs on every POSIX compliant system and works
on arbitrarily large numbers.
In contexts like remailers it is impossible to have the
originator of a message solve puzzles interactively. But
with quasi-synchronous clocks (exact up to a few hours perhaps)
and a small database, it is possible to implement offline
Hashcash. Such a Hashcash Check looks like:
HashCheck
Version: 0.1
To: provos@citi.umich.edu
Bits: 12
Comment: test
Date: 1015030975
Rand: 1530c9285266d00f260983b793861dfd
Hash: 001110111111
It is bound to a recipient (provos@citi.umich.edu) and a date,
so presenting the same check to other parties or to the same party after
a certain period of validity will fail. For the period of validity
the recipient has to store the Rand value and compare incoming
Hashcash Checks against the list of received checks. If the Rand
is on the list or the date outside the validity, the Hashcash is ignored.
And it's all implemented in Perl.
Adam Back has a similiar
scheme with shorter messages intended to be embedded in headers of
other protocols.
Also called Client Puzzles. HashCash is used to prove
expenditure of computing power. This is interesting for
flooding control, e.g.
SMTP Server:
You want to send this email to 10.000 recipients? Well, pay 12 bits of HashCash for each one.
Spammer's MUA: Alright, forget about it.
Adam Back proposed and
implemented HashCash based on partial hash collisions. I wrote a
perl module that implements charge,
pay and check functions for Hashcash in interactive
contexts.