hmac-sha256.mpcl

// -*- go -*-

// This example computes HMAC-SHA256 where the HMAC key is shared as
// two random shares between garbler and evaluator. The garbler's key
// share is:
//
//	keyG: 4de216d2fdc9301e5b9c78486f7109a05670d200d9e2f275ec0aad08ec42af47
//	      fcb59bf460d50b01333a748f3a9efb13e08036d49a26c21ba2e33a5f8a2cf0e7
//
// The evaluator's key share is:
//
//	keyE: f87a00ef89c2396de32f6ac0748f6fa1b641013d46f74ce25cc625904215a675
//	      01c0c7196a2602f6516527958a82271847933c35d170d98bfdb04d2ddf3bb197
//
// The final HMAC key is keyG ^ keyE:
//
//	key : b598163d740b0973b8b312881bfe6601e031d33d9f15be97b0cc8898ae570932
//	      fd755ced0af309f7625f531ab01cdc0ba7130ae14b561b905f53777255174170
//
// The example uses 32-byte messages (Garbler.msg) so with the message:
//
//	msg : Hello, world!...................
//	hex : 48656c6c6f2c20776f726c64212e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e
//
// We expect to get the following HMAC-SHA256 output:
//
//	sum : 60d27dbd14f1e351f20069171fead00ef557d17ac9a41d02baa488ca4b90171a
//
// Now we can run the MPC computation as follows. First, run the
// evaluator with one input: the evaluator's key share:
//
//	./garbled -e -v -i 0xf87a00ef89c2396de32f6ac0748f6fa1b641013d46f74ce25cc625904215a67501c0c7196a2602f6516527958a82271847933c35d170d98bfdb04d2ddf3bb197 examples/hmac-sha256.mpcl
//
// The garbler takes two inputs: the message and the garbler's key
// share:
//
//	./garbled -v -i 0x48656c6c6f2c20776f726c64212e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e,0x4de216d2fdc9301e5b9c78486f7109a05670d200d9e2f275ec0aad08ec42af47fcb59bf460d50b01333a748f3a9efb13e08036d49a26c21ba2e33a5f8a2cf0e7 examples/hmac-sha256.mpcl
//
// The MCP computation providers the expected HMAC result:
//
//	Result[0]: 60d27dbd14f1e351f20069171fead00ef557d17ac9a41d02baa488ca4b90171a
package main

import (
	"crypto/hmac"
)

type Garbler struct {
	msg      []byte
	keyShare [64]byte
}

func main(g Garbler, eKeyShare [64]byte) []byte {
	var key [64]byte

	for i := 0; i < len(key); i++ {
		key[i] = g.keyShare[i] ^ eKeyShare[i]
	}

	return hmac.SumSHA256(g.msg, key)
}