hmac

Documentation

Overview

Package hmac implements the Keyed-Hash Message Authentication Code (HMAC) as defined in U.S. Federal Information Processing Standards Publication 198. An HMAC is a cryptographic hash that uses a key to sign a message. The receiver verifies the hash by recomputing it using the same key.

Receivers should be careful to use Equal to compare MACs in order to avoid timing side-channels:

// ValidMAC reports whether messageMAC is a valid HMAC tag for message.
func ValidMAC(message, messageMAC, key []byte) bool {
	mac := hmac.New(sha256.New, key)
	mac.Write(message)
	expectedMAC := mac.Sum(nil)
	return hmac.Equal(messageMAC, expectedMAC)
}

Index

• func Equal(mac1, mac2 []byte) bool
• func New(h func() hash.Hash, key []byte) hash.Hash

Functions

func Equal

func Equal(mac1, mac2 []byte) bool

Equal compares two MACs for equality without leaking timing information.

func New

func New(h func() hash.Hash, key []byte) hash.Hash

New returns a new HMAC hash using the given hash.Hash type and key. New functions like sha256.New from crypto/sha256 can be used as h. h must return a new Hash every time it is called. Note that unlike other hash implementations in the standard library, the returned Hash does not implement encoding.BinaryMarshaler or encoding.BinaryUnmarshaler.