Reputation
10,233
Next tag badge:
77/100 score
15/20 answers
Badges
3 13 46
Newest
 Nice Answer
Impact
~158k people reached

Aug
21
comment Is a 256 bit HMAC-SHA256 key compromised if the tail is used for identification?
I'm sorry, I understand what you mean now, but I'm not sure if I understand the attack. Using a one way function such as a secure hash should not leak information about the message, even if it is a key. Yes, HMAC (or a KDF really) would be more secure, but I don't see how using a SHA-2 hash would significantly alter security (especially compared with leaking the key bits directly).
Aug
21
comment Diffie-Hellman in the wild
You might want to read NIST SP 800-56A Revision 2 (if you're up to that task). Especially if you want to use two static keys - you don't always want to wind up using the same session key. Oh, and of course you need to trust the public keys using some kind of trust framework as you seem to want to use them for authentication.
Aug
21
comment Is a 256 bit HMAC-SHA256 key compromised if the tail is used for identification?
The question explicitly exposes part of the key already. The user is talking about using part of the key as KCV, before using it as input for HMAC, if I understood correctly. Yes, almost everything is more secure.
Aug
21
answered Is a 256 bit HMAC-SHA256 key compromised if the tail is used for identification?
Aug
21
comment Combining several symmetric ciphers using XOR
Yeah, I thought of that as well, but I'll leave it as an upvoted comment as the goal of the question was to use two dissimilar ciphers anyway. It's always beneficial to use two separate keys though.
Aug
20
comment Real-world example of using ring signature
I'm not sure what I dislike more, the "question" or the way it is asked.
Aug
20
comment Combining several symmetric ciphers using XOR
@PaŭloEbermann Thanks, integrated your comment into the answer.
Aug
20
revised Combining several symmetric ciphers using XOR
added 400 characters in body
Aug
20
comment SHA512 vs HKDF key expansion
Well, as this is the comment section; I would sleep pretty tight even when using the SHA-512 function "poor man's KDF" :)
Aug
20
comment SHA512 vs HKDF key expansion
Maybe a bit late but it's always a good idea to use (at least) one byte to indicate the current protocol for files. That way you can switch implementations when required, without having to re-encrypt everything at the same time.
Aug
20
answered SHA512 vs HKDF key expansion
Aug
20
accepted How does ccrypt work?
Aug
20
comment Hashing a Diffie-Hellman result
Could you please indicate where that quote originated? Because other than said attack I cannot directly come up with an attack at the moment.
Aug
20
comment Hashing a Diffie-Hellman result
This answer seems very much related to my question here. Using the bits of $x$ directly probably has similar characteristics.
Aug
20
comment Combining several symmetric ciphers using XOR
"I have seen this answer but I don't think its relevant anymore. Using multiple ciphers may be needed to defend against NSA mass surveillance." That NSA performs mass survaillance does not mean that NSA has broken - for instance - AES, an algorithm that they did not design. That said, if you want to protect yourself against adversaries like intelligence bureaus (of any country), then you may indeed want to take additional steps. The symmetric cipher is however unlikely to be your weakest link.
Aug
20
revised Using scrypt to generate key + IV/nonce together
added 146 characters in body
Aug
20
revised Using scrypt to generate key + IV/nonce together
rewrote question, same contents, fixed title
Aug
20
comment Using scrypt to generate key + IV/nonce together
The latter would be mainly an option if a good KBKDF is available in your crypto library.
Aug
20
revised Using scrypt to generate key + IV/nonce together
added 5 characters in body
Aug
20
comment Using scrypt to generate key + IV/nonce together
@SEJPM Yes, but that could be mainly because nobody seems to know about KBKDF's :) It should of course also be possible to do this with a good PBKDF without giving an advantage to an attacker. At least HKDF-expand has been designed for this purpose.