SHA512/256 hash

 

About SHA512/256 hash

SHA-512/256 is another variant of the SHA-2 family of cryptographic hash functions, derived from SHA-512. It produces a shorter hash output of 256 bits (32 bytes), which is a compromise between the security of SHA-512 and the shorter output length compared to SHA-512.

Characteristics of SHA-512/256

  1. Fixed-Length Output:

    • SHA-512/256 produces a fixed-length output of 256 bits (32 bytes), regardless of the input data's length.

  2. Input Padding:

    • Similar to other SHA-2 variants, the input message for SHA-512/256 is padded so that its length is congruent to 896 modulo 1024. Padding involves appending a single '1' bit, followed by '0' bits until the message length is 128 bits short of a multiple of 1024. The length of the original message (before padding) is then appended as a 128-bit integer.

  3. Processing in Blocks:

    • SHA-512/256 processes the input message in 1024-bit (128-byte) blocks, similar to SHA-512.

  4. Initialization Vector (IV):

    • SHA-512/256 uses the same initial state as SHA-512, which consists of eight 64-bit words:
      • H0 = 0x22312194FC2BF72C
      • H1 = 0x9F555FA3C84C64C2
      • H2 = 0x2393B86B6F53B151
      • H3 = 0x963877195940EABD
      • H4 = 0x96283EE2A88EFFE3
      • H5 = 0xBE5E1E2553863992
      • H6 = 0x2B0199FC2C85B8AA
      • H7 = 0x0EB72DDC81C52CA2

  5. Compression Function:

    • The compression function of SHA-512/256 is the same as SHA-512, involving 80 rounds of processing for each 1024-bit block. Each round uses different logical functions, constants, and message schedule operations:
      • Logical functions include bitwise operations (AND, OR, XOR, NOT), additions, and shifts/rotations.
      • Constants are derived from the first 64 bits of the fractional parts of the cube roots of the first 80 prime numbers.

Algorithm Steps

  1. Initialization:

    • Initialize the state variables (H0 to H7) to the predefined values.

  2. Padding:

    • Pad the input message according to the specified padding rules.

  3. Processing:

    • Divide the padded message into 1024-bit blocks.
    • For each block, perform the 80 iterations of the compression function, updating the state variables.

  4. Output:

    • After processing all blocks, use the first four state variables (H0 to H3) to produce the final 256-bit hash value.

Security and Usage

  • Security:

    • Collision Resistance: SHA-512/256 inherits strong collision resistance from SHA-512, making it highly secure against collision attacks.
    • Preimage Resistance: SHA-512/256 is resistant to preimage attacks, ensuring that it is computationally infeasible to find an input that hashes to a given output.
    • Second-Preimage Resistance: SHA-512/256 also offers strong resistance to second-preimage attacks, ensuring that it is difficult to find a second input with the same hash as a given input.
    • The shorter output length compared to SHA-512 provides efficiency benefits while maintaining robust security.

  • Usage:

    • SHA-512/256 is used in various security applications where a compromise between the security of SHA-512 and the shorter output length is desired.
    • It is particularly suitable for applications requiring high security assurance and where the shorter hash length is advantageous, such as in digital signatures, SSL/TLS certificates, and integrity verification.

Summary

SHA-512/256 is a cryptographic hash function derived from SHA-512, producing a 256-bit hash value. It offers strong security properties, including resistance to collisions, preimage attacks, and second-preimage attacks. SHA-512/256 strikes a balance between security and efficiency, making it suitable for a variety of cryptographic applications where a shorter but still robust hash output is required. Its adoption in modern security protocols reflects its reliability and effectiveness in ensuring data integrity and authenticity.