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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.
The following tables compare general and technical information for a number of cryptographic hash functions. See the individual functions' articles for further information.
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]
This client starts the process by sending a clientHello message to the server that includes the version of TLS being used and a list of cipher suites in the order of the client's preference. In response, the server sends a serverHello message that includes the chosen cipher suite and the session ID.
[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 ...
Because most users typically choose short passwords formed in predictable ways, passwords can often be recovered from their hashed value if a fast hash is used. Searches on the order of 100 billion tests per second are possible with high-end graphics processors.