CodesInChaos
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 Apr 1 revised Is it safe to encrypt random data using ECB mode? added 32 characters in body Apr 1 answered Is it safe to encrypt random data using ECB mode? Apr 1 comment Average/approximate difference in value between valid consecutive $x$ coordinates in ECC? $d$ should be pretty close to 2. Mar 31 comment Is it safe to encrypt random data using ECB mode? Can't answer that without context. But there is one thing all the modes you mentioned lack: Integrity checks/MACs. Mar 30 comment Is there any pattern in points on EC? Even if you're given a compressed point, i.e. you don't know y, you can still check if x^3+ax+b is a square. This can be avoided by either randomly choosing a point from the curve or its twist (with the correct probabilities) or using something fancy, like elligator. Mar 27 comment Can I construct a zero-knowledge proof that I solved a Project Euler problem? Checking if you have the same answer as somebody else is the Socialist millionaire problem. Mar 26 comment Blum primes [x=3(mod 4)] zero knowledge proof? "I can, without revealing factors, show that n has two prime factors" -- how? I'm not aware of any way to do this. Using MPC to jointly produce a modulus is the approach that comes closest to achieving this. Mar 26 revised NTRU Encryption deleted 6 characters in body Mar 25 comment Are modes of operation algorithms practical? Kerckhoffs's principle Mar 25 comment Now that quantum computers have been out for a while, has RSA been cracked? @MichaelJonathanSimpson When you're worried about quantum computers, larger RSA keys won't offer much peace of mind. The number of required ideal qbits is linear in the key size. With error correction that increase might be steeper, but still not that big. Once a QC can factor a 2048 bit key it will probably only be a few years to factoring a 4096 bit key. Mar 25 comment Cycles in SHA256 With a blockcipher (which is a permutation), the cycle length would be around $2^{255}$ with a hash the cycle length is around $2^{128}$. But of course these are just statistical values and both shorter and longer cycles exist. Mar 24 reviewed Satisfactory Additional Data in AEAD (Chacha20-poly1305 libsodium) Mar 23 comment What is the best hash for HMAC? There are only two significant SHA-2 variants, SHA-256 and SHA-512. All the other variants only differ by truncation and have different IVs. Mar 23 comment Is it safe to use PBEWithMD5AndDES? If this is really DES and not 3DES then it's very weak. Mar 22 comment Difference between the TLS cipher suites? Nobody uses DSS suites/certificates. If you want better performance, go with the elliptic curve equivalent, ECDHE_ECDSA Mar 21 comment Coding of unsigned int to prevent guessing next ID Either use a 32 bit blockcipher like Skip32 or use proper format preserving encryption (tricky to implement). Mar 21 comment Are factorization algorithms parallelizable? @fkraiem I consider the efficiency of factoring algorithms on-topic for crypto.se. Mar 21 comment Are factorization algorithms parallelizable? 1) don't use BBS 2) The standard factoring algorithm is the number field sieve. There exists a variant called Batch NFS which at least in theory reduces the average cost for factoring if you attack multiple moduli. But I don't know if it leads to a practical improvement for typical key sizes. I'm also not sure to which degree it can be parallelized. Mar 21 comment Security of simple Skein PBKDF mentioned in the paper It's not memory hard and is comparable to PBKDF2. Scrypt and bcrypt are still better. Mar 21 comment Is it safe to prefix the a key with a known value? Since HMAC exhibits weird behaviour with variable length keys, I wouldn't really count it as an exception.