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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.
Version Platforms SSL 2.0 (insecure) SSL 3.0 (insecure) TLS 1.0 (deprecated) TLS 1.1 (deprecated) TLS 1.2 TLS 1.3 EV certificate SHA-2 certificate ECDSA certificate BEAST CRIME POODLE (SSLv3) RC4 FREAK Logjam Protocol selection by user Microsoft Internet Explorer Mobile [n 20] 7–9 Windows Phone 7, 7.5, 7.8: Disabled by default [57] Yes Yes
Office 2013 uses 128-bit AES, again with hash algorithm SHA-1 by default. [6] It introduces SHA-512 hashes in the encryption algorithm, making brute-force and rainbow table attacks slower. [citation needed] Office 2016 uses, by default, 256-bit AES, the SHA-2 hash algorithm, 16 bytes of salt and CBC (cipher block chaining). [7]
Per CNSSP-15, the 256-bit elliptic curve (specified in FIPS 186-2), SHA-256, and AES with 128-bit keys are sufficient for protecting classified information up to the Secret level, while the 384-bit elliptic curve (specified in FIPS 186-2), SHA-384, and AES with 256-bit keys are necessary for the protection of Top Secret information.
SHA-2 basically consists of two hash algorithms: SHA-256 and SHA-512. SHA-224 is a variant of SHA-256 with different starting values and truncated output. SHA-384 and the lesser-known SHA-512/224 and SHA-512/256 are all variants of SHA-512. SHA-512 is more secure than SHA-256 and is commonly faster than SHA-256 on 64-bit machines such as AMD64.
CNSA 2.0 includes: [2] Advanced Encryption Standard with 256 bit keys; Module-Lattice-Based Key-Encapsulation Mechanism Standard (ML-KEM aka CRYSTALS-Kyber) with parameter set ML-KEM-1024; Module-Lattice-Based Digital Signature Standard (ML-DSA aka CRYSTALS-Dilithium) with parameter set ML-DSA-87; SHA-2 with 384 or 512 bits
Algorithm and variant Output size (bits) Internal state size (bits) Block size (bits) Rounds Operations Security against collision attacks (bits) Security against length extension attacks