Figure 4: ANSI X9.31 padding format. Message representative consists of fixed padding followed by the hash value, a hash function identifier, and additional padding. 6b, ba, bb, and cc are byte values in hexadecimal. The hash function identifier is 1 byte long and can identify any of a short list of registered hash functions. The message representative is the same length in bytes as the signer's RSA modulus. For this format, the modulus length in bits must be a multiple of 8.