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SHA-2 (Secure Hash Algorithm 2) is a set of cryptographic hash functions designed by the United States National Security Agency (NSA) and first published in 2001. [ 3 ] [ 4 ] They are built using the Merkle–Damgård construction , from a one-way compression function itself built using the Davies–Meyer structure from a specialized block cipher.
SHA-2: A family of two similar hash functions, with different block sizes, known as SHA-256 and SHA-512. They differ in the word size; SHA-256 uses 32-bit words where SHA-512 uses 64-bit words. There are also truncated versions of each standard, known as SHA-224, SHA-384, SHA-512/224 and SHA-512/256. These were also designed by the NSA.
SHA-2 with 384 bits, Diffie–Hellman key exchange with a minimum 3072-bit modulus, and; RSA with a minimum modulus size of 3072. [2] The CNSA transition is notable for moving RSA from a temporary legacy status, as it appeared in Suite B, to supported status. It also did not include the Digital Signature Algorithm. This, and the overall ...
Let hash(m) = x m mod n, where n is a hard-to-factor composite number, and x is some prespecified base value. A collision x m 1 ≡ x m 2 (mod n) reveals a multiple m 1 − m 2 of the multiplicative order of x modulo n. This information can be used to factor n in polynomial time, assuming certain properties of x.
The sender is required to find a message whose hash value begins with a number of zero bits. The average work that the sender needs to perform in order to find a valid message is exponential in the number of zero bits required in the hash value, while the recipient can verify the validity of the message by executing a single hash function.
Even though MD2 is not yet fully compromised, the IETF retired MD2 to "historic" status in 2011, citing "signs of weakness". It is deprecated in favor of SHA-256 and other strong hashing algorithms. [4] Nevertheless, as of 2014, it remained in use in public key infrastructures as part of certificates generated with MD2 and RSA. [citation needed]
The algorithm starts with an initial value, the initialization vector (IV). The IV is a fixed value (algorithm- or implementation-specific). For each message block, the compression (or compacting) function f takes the result so far, combines it with the message block, and produces an intermediate result. The last block is padded with zeros as ...
[12] [10] [13] NIST formally deprecated use of SHA-1 in 2011 and disallowed its use for digital signatures in 2013, and declared that it should be phased out by 2030. [14] As of 2020, chosen-prefix attacks against SHA-1 are practical. [6] [8] As such, it is recommended to remove SHA-1 from products as soon as possible and instead use SHA-2 or ...