sha256

SHA-256 circuits for multiple blocks

This directory contains a SHA-256 circuit adapted from Nigel Smart's Bristol Fashion SHA-256 function here. This circuit is being used when we assemble the HMAC function.

Syntax

• Alice's Input: 768 bits
  • First 512 bits, the SHA-256 input; often it needs to be padded.
  • Following 256 bits, the SHA-256 state; note that the initial state is not zero but instead some constants.
• Output: 256 bits.

Feeding the initial state

The following digests are the common constants for SHA-256, from wolfssl.

word32 digest[8];
digest[0] = 0x6A09E667L;
digest[1] = 0xBB67AE85L;
digest[2] = 0x3C6EF372L;
digest[3] = 0xA54FF53AL;
digest[4] = 0x510E527FL;
digest[5] = 0x9B05688CL;
digest[6] = 0x1F83D9ABL;
digest[7] = 0x5BE0CD19L;

One can see the example code in generate_handshake_circuits.cpp for how to input these constants, where the endianness becomes slightly complicated.