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In particular, a precomputed table would need to cover the string [salt + hash] rather than simply [hash]. The modern shadow password system, in which password hashes and other security data are stored in a non-public file, somewhat mitigates these concerns. However, they remain relevant in multi-server installations which use centralized ...
SHA-2 (Secure Hash Algorithm 2) is a set of cryptographic hash functions designed by the United States National Security Agency (NSA), first published in 2001. They are built using the Merkle–Damgård structure, from a one-way compression function itself built using the Davies–Meyer structure from a (classified) specialized block cipher.
The security reduction of HMAC does require them to be different in at least one bit. [citation needed] The Keccak hash function, that was selected by NIST as the SHA-3 competition winner, doesn't need this nested approach and can be used to generate a MAC by simply prepending the key to the message, as it is not susceptible to length-extension ...
Intrinsically keyed hash algorithms such as SipHash are also by definition MACs; they can be even faster than universal-hashing based MACs. [ 9 ] Additionally, the MAC algorithm can deliberately combine two or more cryptographic primitives, so as to maintain protection even if one of them is later found to be vulnerable.
This gives a somewhat stronger notion of security than just relying on complex mixing of bits as in the classical approach. A cryptographic hash function has provable security against collision attacks if finding collisions is provably polynomial-time reducible from a problem P which is supposed to be unsolvable in polynomial time. The function ...
A hash function uniform on the interval [0, n − 1] is n P(key) / 2 b. We can replace the division by a (possibly faster) right bit shift: n P(key) >> b. If keys are being hashed repeatedly, and the hash function is costly, then computing time can be saved by precomputing the hash codes and storing them with the keys.
Hash-based signature schemes use one-time signature schemes as their building block. A given one-time signing key can only be used to sign a single message securely. Indeed, signatures reveal part of the signing key. The security of (hash-based) one-time signature schemes relies exclusively on the security of an underlying hash function.
IPsec Virtual Private Network and more; IEEE P1363 covers most aspects of public-key cryptography; Transport Layer Security (formerly SSL); SSH secure Telnet and more; Content Scrambling System (CSS, the DVD encryption standard, broken by DeCSS)