8,799 reputation
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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 2 years, 9 months
seen 2 days ago

Jun
29
revised inverse problem about scalar multiplication on elliptic curve
edited tags
Jun
29
comment PAK Diffie-Hellman vs. sharing high-entropy key
The problem is how would to generate the shared key without allowing impersonation. If you can do that securely, then go for it. Passwords are just a concession to the feeble human mind.
Jun
29
comment Proof of work for determining whether a number is prime?
@ThePiachu Trial division only works on really small primes since it's cost is exponential in the length of the prime ($2^{n/2}$ trial divisions for an $n$ bit prime). So it scales perhaps up to 160 bits with a lot of work. Good primality tests have polynomial runtime, something like $n^4$. Please read Primality test on wikipedia
Jun
29
comment Proof of work for determining whether a number is prime?
What is the actual problem you're trying to solve? Sounds like an XY problem. Checking if a number is prime is fast (no need to distribute), for factoring there are much faster algorithms than trial divisions and as proof of work this isn't better than partial hash pre-images. So what's the point?
Jun
28
comment ECDSA Compressed public key point back to uncompressed public key point
@ThomasPornin I didn't look into other curve shapes, but at least for Montgomery curves you don't need decompression for DH when you use x/z coordinates.
Jun
28
comment ECDSA Compressed public key point back to uncompressed public key point
For ECDH you probably don't need to uncompress at all. For ECDSA you take the curve equation and solve for the unknown coordinate. The only tricky part is the square-root, which AFAIK can be solved by modular exponentiation.
Jun
28
comment Is my one time pad cipher secure?
@kylek If "suitable for cryptographic use" is enough then you're missing the point of a one-time pad, which is being provably secure by being completely random. If you use pseudo-random pads you could use a stream cipher instead. Just as secure, but much less inconvenient to use.
Jun
27
comment What are the standard procedures in cryptanalysis to analyze unknown ciphertext?
Next time please include essential information in the original question instead of adding it later on. Analyzing pure ciphertext is really hard, but many concrete implementations such as PGP will have a container around the ciphertext, so it's obvious when they were used. Additional context would still be useful, for example do you talk about encrypted emails or encrypted connections?How does the data you captured look? Binary? Base64? Any headers?... With the changes it's probably a better fit for security.SE.
Jun
27
comment What are the standard procedures in cryptanalysis to analyze unknown ciphertext?
The point is that no serious civilian cryptographer does ciphertext only cryptoanalysis. That's a waste of time. You can't break bad ciphers that way, only really really shitty ones. So there are no standard procedures for it.
Jun
27
comment What are the standard procedures in cryptanalysis to analyze unknown ciphertext?
Ciphertext only cryptoanalysis has fallen out of fashion. Modern crypto needs to be secure against attackers who know everything about your system except the key. Even with Enigma the attackers stole some machines to learn how they work. So Step 1 is: Obtain the algorithm used to produce the ciphertext
Jun
27
comment Rating a steganographic system using Blum Blum Shub to locate hidden bits
BBS is a subtle algorithm and the security proof is much weaker than most people think. I wouldn't use it over a normal stream cipher in a real project.
Jun
27
comment Rating a steganographic system using Blum Blum Shub to locate hidden bits
Why do you prefer BBS over a normal stream cipher, such as AES-CTR or Salsa20?
Jun
27
comment Elliptic curve parameter generation
Typical co-factors are 1, 2, 4 and 8 i.e. very small.
Jun
26
comment How to communicate by email with forward secrecy and deniability?
I don't see why you need an online key-exchange for non forward secure encryption/mac. You could simply compute the shared DH key between the two long-term keys and prove knowledge of that key by computing a MAC. That way you get some degree of authentication and deniability.
Jun
26
reviewed Approve suggested edit on serpent tag wiki excerpt
Jun
26
reviewed Approve suggested edit on ocb tag wiki
Jun
26
reviewed Approve suggested edit on twofish tag wiki excerpt
Jun
26
reviewed Approve suggested edit on twofish tag wiki
Jun
26
reviewed Approve suggested edit on rijndael tag wiki excerpt
Jun
26
reviewed Approve suggested edit on crc tag wiki