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11149
bio website vyznev.net
location Helsinki, Finland
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visits member for 3 years
seen Aug 30 at 14:00

I'm a PhD student in biomathematics, working on stochastic individual-based models of evolution in spatially structured populations. My other interests include cryptography, programming games and puzzles, photography and graphic design.

I started programming (in AmigaBASIC) when I was 10 years old. Nowadays, I'm most comfortable using Perl, C and JavaScript. I know Java and PHP too, but I can't really say I like them. I also know some Python, but not as much as I'd like.


CC-Zero Please consider any (original) code I post to Stack Overflow and other Stack Exchange sites to be released under CC-Zero unless stated otherwise. You may do whatever you want with it and don't have to credit me in any way, although of course that would be nice.


I'm the main author and maintainer of the Stack Overflow Unofficial Patch (SOUP), a user script for browsers with GreaseMonkey-compatible user script support (Firefox, Chrome, Opera, possibly Safari) that fixes or works around a number of outstanding issues with the Stack Exchange user interface.

I tend to answer a lot more questions than I ask. Some answers I'm rather proud of:


May
8
comment Decrypt a public encrypted message and Sign a signature, how the math is different?
@CodesInChaos: I think this could actually be a pretty good "FAQ" question, and your comment, with some embellishment (e.g. compare RSA signing with RSA encryption and DSA / ElGamal signing with ElGamal encryption), could make a good answer for it. I may try to write one later, unless someone else does it first.
May
5
comment Difference between a nonce and IV
Related, but less specific question: crypto.stackexchange.com/questions/3965/…
May
4
comment How do I produce a stream of secure random numbers from AES-Counter mode?
@owlstead: I'm not aware of any attacks for $E_K(K)$, but there's definitely an attack for, say, $E_K(D_K(0))$.
Apr
26
comment How secure would HMAC-SHA3 be?
@fgrieu: As far as I can tell, the argument is that Keccak provides this level of security when used with the generic sponge MAC construction (= prepend key to message; CSF §5.11.2), of which the inner HMAC pass can be seen as an instance. That security, in turn, is claimed to follow from the Keccak flat sponge claim (Keccak reference §1.5), which is a pretty strong claim that, loosely speaking, says that Keccak is as good as a random oracle against attacks using $\lll 2^{c/2}$ work.
Apr
25
comment Solving Vignere Encryption
@vignere_solve: OK, here's the hint: I was wrong about letter case. The correct cipher alphabet has 64 characters: AZ, az, 09, + and /. It just happens that, with this particular alphabet and key, most lowercase letters are encrypted to uppercase ones, and vice versa.
Apr
23
comment Solving Vignere Encryption
@vignere_solve: No problem. Ps. I did solve it, and it turns out that one of the early assumptions I made is wrong. However, you can still decode most of the text despite the wrong assumption, and, once you do, it's not hard to figure out what the mistake it. Let me know if you need a further hint.
Apr
23
comment What can I change in Lane to
Your question title appears to
Apr
15
comment Block cipher and parity of permutation
Generalizing your first example, if we start with any permutation, and extend the state space being permuted by at least one extra bit (which does not affect the permutation and is not affected by it), then the resulting extended permutation will be even.
Apr
1
comment What is h in the improved solution of RSA algorithm?
Ugh... I looked at the paper to try and fix the broken math formatting in the question, but it turns out to be like that in the paper too. :-( Honestly, most of the paper looks a lot like SCIgen output anyway.
Mar
23
comment Certificate signature with SHA-1 and RSA: where do 1888 bits come from?
See also identical question on security.SE.
Mar
23
comment Choice of reduction polynomial in Whirlpool's internal cipher
Ps. See also this related question.
Mar
23
comment Is this approach to generating a “random” number from a sha512 hash effective?
The list of participants' names might not have enough entropy to prevent you from cheating even without help from others. In particular, if you can guess who might sign up for the raffle (and in what order), you could compile a bunch of likely participant lists in advance, and, after testing a large number of possible secret inputs against those lists, select the one that has the best chance of giving you a favorable outcome if the actual participant list happens to match one of your guesses.
Mar
13
comment I need a 64-bit cryptographic hash for 96 bits of data
+1. The birthday bound is a harsh mistress.
Feb
20
comment How to represent a 32-byte SHA2 hash in the shortest possible string?
For case-insensitive file systems, it's probably best to stick with base 32 or 36, which can be encoded using single-case letters and numbers. In particular, the distinct printable ASCII characters allowed in Windows file names are not quite enough to encode six bits per character: there are 9 reserved characters and 26 equivalent upper/lowercase pairs, leaving only 60 usable characters (including space, which you don't seem to count; also, some file systems may have additional reserved characters).
Feb
13
comment Can someone explain the ECB Penguin?
@JoshBond: The "pattern" arises because pixels and cipher blocks don't line up exactly: an uncompressed true-color pixel takes up three bytes, while most common block ciphers encrypt blocks of either 8 or 16 bytes (64 or 128 bits).
Jan
30
comment Is the Couvreur et al. polynomial time attack on McEliece practical?
Hi, fractal, and welcome to Cryptography Stack Exchange! I've edited your question to add some detail and make it a better fit to our site. Please don't hesitate to correct any mistakes or omissions I may have introduced while doing so.
Jan
29
comment Avoiding overflow when encrypting with RSA
Also, just to clarify your last sentence above, the "flaws" for small $e$ (like Coppersmith's attack) only appear if one does not use a secure padding scheme (e.g. OAEP). With proper padding, RSA is secure even for $e=3$; without proper padding, it may not be secure for any $e$.
Jan
29
comment Efficient Robust Private Set Intersection Additive ElGamal
I just approved this edit suggestion from an anonymous user. (It still needs someone else to approve it.) I assume that was you? You might want to register an account here, so that you'll be able to edit your posts more easily.
Jan
14
comment Many time pad attack
@e-sushi: How does one attack a two-time pad (i.e. one time pad with key reuse)? would be a closer match; it even appears to be about the same Coursera exercise. This one's a little bit more specific, though, since the other question is about general solution methods while this one is specifically about the hint. (Also, the other question is kind of messy.) I wouldn't necessarily object to having them merged, but only if the questions are also edited to combine them.
Jan
12
comment Difference between CBC-MAC and CMAC
@figlesquidge: While the information requested probably is obtainable from Wikipedia, it's not very clearly presented there. IMO, this is a perfectly good reference question, and I'm hoping to see a concise and comprehensive answer summarizing the main differences.