hmac.go raw

   1  package hmac
   2  
   3  import "common/crypto/sha256"
   4  
   5  const blockSize = 64
   6  
   7  // Sum computes HMAC-SHA256(key, message).
   8  func Sum(key, message []byte) [32]byte {
   9  	// If key > blockSize, hash it.
  10  	var k [blockSize]byte
  11  	if len(key) > blockSize {
  12  		h := sha256.Sum(key)
  13  		copy(k[:], h[:])
  14  	} else {
  15  		copy(k[:], key)
  16  	}
  17  
  18  	var ipad, opad [blockSize]byte
  19  	for i := 0; i < blockSize; i++ {
  20  		ipad[i] = k[i] ^ 0x36
  21  		opad[i] = k[i] ^ 0x5c
  22  	}
  23  
  24  	// inner = SHA256(ipad || message)
  25  	inner := make([]byte, blockSize+len(message))
  26  	copy(inner, ipad[:])
  27  	copy(inner[blockSize:], message)
  28  	innerHash := sha256.Sum(inner)
  29  
  30  	// outer = SHA256(opad || inner_hash)
  31  	var outer [blockSize + 32]byte
  32  	copy(outer[:blockSize], opad[:])
  33  	copy(outer[blockSize:], innerHash[:])
  34  	return sha256.Sum(outer[:])
  35  }
  36