SHA-256
SHA-256 stands for Secure Hash Algorithm 256-bit, and is used for cryptographic security. SHA-256 generates an almost-unique 256-bit signature for a text. The hashing algorithm compresses data of any size into an alphanumeric string that cannot be easily reverse engineered, keeping the original data secret and secure while being useful for validating input data. It was developed in part with the US National Security Agency (NSA) and is used by Bitcoin and many other cryptocurrencies for mining and creating addresses.
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. 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.
| Secure Hash Algorithms | |
|---|---|
| Concepts | |
| hash functions · SHA · DSA | |
| Main standards | |
| SHA-0 · SHA-1 · SHA-2 · SHA-3 | |
| General | |
|---|---|
| Designers | National Security Agency |
| First published | 2001 |
| Series | (SHA-0), SHA-1, SHA-2, SHA-3 |
| Certification | FIPS PUB 180-4, CRYPTREC, NESSIE |
| Detail | |
| Digest sizes | 224, 256, 384, or 512 bits |
| Structure | Merkle–Damgård construction with Davies–Meyer compression function |
| Rounds | 64 or 80 |
| Best public cryptanalysis | |
| A 2011 attack breaks preimage resistance for 57 out of 80 rounds of SHA-512, and 52 out of 64 rounds for SHA-256. Pseudo-collision attack against up to 46 rounds of SHA-256. SHA-256 and SHA-512 are prone to length extension attacks. By guessing the hidden part of the state, length extension attacks on SHA-224 and SHA-384 succeed with probability 2−(256−224) = 2−32 > 2−224 and 2−(512−384) = 2−128 > 2−384 respectively. | |
SHA-2 includes significant changes from its predecessor, SHA-1. The SHA-2 family consists of six hash functions with digests (hash values) that are 224, 256, 384 or 512 bits: SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, SHA-512/256. SHA-256 and SHA-512 are novel hash functions computed with eight 32-bit and 64-bit words, respectively. They use different shift amounts and additive constants, but their structures are otherwise virtually identical, differing only in the number of rounds. SHA-224 and SHA-384 are truncated versions of SHA-256 and SHA-512 respectively, computed with different initial values. SHA-512/224 and SHA-512/256 are also truncated versions of SHA-512, but the initial values are generated using the method described in Federal Information Processing Standards (FIPS) PUB 180-4.
SHA-2 was first published by the National Institute of Standards and Technology (NIST) as a U.S. federal standard (FIPS). The SHA-2 family of algorithms are patented in US. The United States has released the patent under a royalty-free license.
As of 2011, the best public attacks break preimage resistance for 52 out of 64 rounds of SHA-256 or 57 out of 80 rounds of SHA-512, and collision resistance for 46 out of 64 rounds of SHA-256.
