Module: WebriskHash::Hash

Extended by:
Hash
Included in:
WebriskHash, Hash
Defined in:
lib/webrisk_hash/hash.rb

Instance Method Summary collapse

Instance Method Details

#truncated_sha256_prefix(str, bits) ⇒ String

Compute SHA256 hash and return truncated prefix

For Web Risk, a hash prefix consists of the most significant 4-32 bytes of a SHA256 hash (32 to 256 bits)

Examples:

FIPS-180-2 Example B1 (32 bits)

truncated_sha256_prefix("abc", 32)
# => "\xBA\x78\x16\xBF" (4 bytes)
# Full SHA256: ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad

FIPS-180-2 Example B2 (48 bits)

input = "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq"
truncated_sha256_prefix(input, 48)
# => "\x24\x8D\x6A\x61\xD2\x06" (6 bytes)
# Full SHA256: 248d6a61d20638b8e5c026930c3e6039a33ce45964ff2167f6ecedd419db06c1

Parameters:

  • The string to hash (suffix/prefix expression)

  • Number of bits to return (will be converted to bytes)

Returns:

  • Binary string containing the hash prefix



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# File 'lib/webrisk_hash/hash.rb', line 27

def truncated_sha256_prefix(str, bits)
  len = bits / 8
  digest = ::Digest::SHA256.digest(str)
  digest.byteslice(0, len)
end