10,594 reputation
11044
bio website vyznev.net
location Helsinki, Finland
age
visits member for 2 years, 8 months
seen 22 hours ago

I'm not really a cryptographer, I just play one on the internet.

Seriously, I'm just a programmer and mathematician interested in puzzles and information security. I don't have any kind of formal crypto training, but I've picked up a few things here and there over the years. Topics I'm particularly interested in include protocol design and analysis, classical ciphers and information-theoretically secure crypto techniques such as one time pads and secret sharing schemes.

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.


Aug
27
revised Should I delete cryptographic data from memory?
edited tags
Aug
27
reviewed Leave Open hardware and software optimizations for Salsa20
Aug
27
reviewed Leave Open Three-way key exchange with elliptic curves without pairing
Aug
26
comment The specification of modern, non-communicating cipher machinery
I agree with @owlstead, and have voted to close this question as essentially unanswerable. There might be a meaningful and practical question hidden behind it, but if you want it answered, you'll have to be more explicit about what it is. As currently written, I'm fairly sure the only kind of literature such questions have been considered in is science fiction and fantasy. (And for that, we have another Stack Exchange site.)
Aug
26
comment Lagrange Interpolation for finite field GF(2^8), for Secret Reconstruction
Is the result you're getting actually 104, not 14? Because that's what you should be getting if you calculate 17 × 3 + 34 × 3 + 61 in GF(2^8). The reason you're not getting 10 is that the points (1,17), (2,34) and (3,61) do not satisfy y = 5x² + 2x + 10 in GF(2^8). To make the reconstruction work in GF(2^8), you need to calculate the shares in that field too; see poncho's second answer for details.
Aug
26
comment Lagrange Interpolation for finite field GF(2^8), for Secret Reconstruction
If you're using operator overloading to implement Galois field arithmetic, remember that you need to overload addition and subtraction too. And don't forget to overload the non-assignment versions of the operators, either.
Aug
26
awarded  Revival
Aug
25
revised Multiplication/Division in Galois Field (2^8)
added 4 characters in body
Aug
25
revised Multiplication/Division in Galois Field (2^8)
added 1034 characters in body
Aug
25
answered Multiplication/Division in Galois Field (2^8)
Aug
25
revised What is the origin of the word “Keccak”?
edited tags
Aug
25
answered What is the origin of the word “Keccak”?
Aug
25
comment Generating an IV for ESP 3DES-CBC
@JuanAndrés: For details on the "fixed IV trick", see crypto.stackexchange.com/questions/5421/…. Basically, it's just a clever way to perform both the NIST-recommended IV derivation and the actual CBC encryption using a single call to a CBC encryption function.
Aug
23
comment Is it theoretically possible to construct a string that contain its own hash value?
@Mys_721tx: If you have a practical chosen-prefix preimage attack on the hash, then you can use it to find such a string: just choose a prefix equal to the desired hash value. I'm not familiar with the attacks on MD4, but most attacks on Merkle-Damgård style hashes do tend to allow chosen prefixes. That said, AFAIK the best known preimage attacks on MD4 aren't really that practical yet: the Laurent attack still needs about $2^{102}$ compression function computations to find a full preimage.
Aug
22
awarded  Yearling
Aug
22
answered SHA256 Round Equivalence
Aug
22
comment Is it theoretically possible to construct a string that contain its own hash value?
@RickyDemer: Thanks, fixed.
Aug
22
revised Is it theoretically possible to construct a string that contain its own hash value?
edited body
Aug
22
revised SHA256 Round Equivalence
formatting, copyedit
Aug
22
comment How resilient to attackers with extreme resources available is this encryption method?
I believe the reason why the answers you're getting are so all over the place is that you haven't defined the scenario fully. In particular, are you trying to implement a secure communication channel or secure file storage? If the latter, what exactly is the authentication part used for; who's authenticating what to whom, and for what purpose? What kind of resources do the legitimate users and/or servers have? Can your users securely store random encryption keys? Can they store random 256-bit keys at all, even insecurely?