CodesInChaos

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	5,954 reputation	bio	website	github.com/CodesInChaos	visits	member for	1 year, 10 months
1927 badges		location	Munich, Germany		seen	22 hours ago

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Mar 19	comment	Brute forcing an HMAC If it's a proper key (128 random bits) then it's completely infeasible. If the key is derived from a password, it depends on the password and the derivation function. But in that case you don't attack HMAC, you attack the password.
Mar 19	comment	Encryption with Deduplication This is known as convergent encryption. Unless your question has any aspects not covered by that question, we could close it as a duplicate ;)
Mar 19	comment	decrypting unreadable string Perhaps it's encrypted with a AES outputting a single block using ANSI (or similar) encoding.
Mar 18	reviewed	Approve suggested edit on computing inverses in truncated polynomial rings manually for NTRU encryption
Mar 18	reviewed	Approve suggested edit on When confusion is applied during encryption?
Mar 18	reviewed	Approve suggested edit on Where to store the private key and the public key in a communication protocol
Mar 18	comment	Efficient algorithm for remainder calculation over prime field for ECC implementation? @venkat Primes in ECC are often specifically chosen so they allow more efficient reductions.
Mar 18	revised	Efficient algorithm for remainder calculation over prime field for ECC implementation? added 6 characters in body
Mar 18	comment	Export from US of crypto software with key-size > 56 bits still needs permission? You often need to register your software, but as long as you don't export to a couple of blacklisted states, that's mostly a formality. For open source software the rules are even more relaxed. So effectively it's just a bit of bureaucracy thrown at you.
Mar 18	awarded	Fanatic
Mar 18	comment	How large should a Diffie-Hellman p be if the messages are encrypted? You should also ask yourself what you're using DH for, if you already have a shared key? Forward secrecy?
Mar 18	comment	How large should a Diffie-Hellman p be if the messages are encrypted? Messages being encrypted doesn't make a difference. Just use a standard group designed for diffie-hellman.
Mar 17	comment	How comparable is OFB to a one-time pad? OFB is a synchronous stream cipher, and OTP is one as well.
Mar 17	revised	Low Public Exponent Attack for RSA added 45 characters in body; edited tags
Mar 16	comment	Is AES-256 a post-quantum secure cipher or not? The attack you link does not work when you use AES with a random key in a normal way. If you only need AES to be a pseudo-random-permutation (PRP), then it's no attack at all. AES was primarily designed as a PRP, resistance to related key attacks was only a secondary goal(if it was a goal at all). It is only an attack if you use AES in an unusual way where the attacker has control over the key. For example if you try building a hash function from AES, this attack might become an issue.
Mar 16	comment	Is AES-256 a post-quantum secure cipher or not? Calling a related key attack on AES "practical" isn't really true. The way AES is supposed to be used is with a random key. So this attack can't be used against any "normal" AES use.
Mar 11	comment	Is there an efficient way to hide the encrypted plaintext length with a block cipher? I don't get your question, but you can use AES-CTR as PRNG. Stream ciphers and the expansion part of a PRNG are essentially the same thing. But that way the only input will be the key.
Mar 11	comment	Would a “Triple AES” (in the sense of how Triple Des works) serve for a dramatic increase in safety? If were were to use double encryption, I'd go with AES xor ChaCha (or Salsa20). Tahoe-LAFS will use some variant of this for its 100 year crypto.
Mar 11	comment	Would a “Triple AES” (in the sense of how Triple Des works) serve for a dramatic increase in safety? sha256 with salts for stored passwords <- that's weak. You need some iterated scheme, like PBKDF2, bcrypt or scrypt. See How to securely hash passwords?
Mar 11	comment	Would a “Triple AES” (in the sense of how Triple Des works) serve for a dramatic increase in safety? DES is broken because its key is small, not because cryptoanalysis advanced so much. An AES256 key is large enough. So the analogy isn't that useful. While it's likely that 3AES will be stronger that AES, I'd prefer a different algorithm, since you're trying to guard against cryptoanalysis of AES.