Function ekmFromMasterSecret

prf.go:254–283

ekmFromMasterSecret generates exported keying material as defined in RFC 5705.

(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte)

// ekmFromMasterSecret generates exported keying material as defined in RFC 5705.
func ekmFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte) func(string, []byte, int) ([]byte, error) {
	return func(label string, context []byte, length int) ([]byte, error) {
		switch label {
		case "client finished", "server finished", "master secret", "key expansion":
			// These values are reserved and may not be used.
			return nil, fmt.Errorf("crypto/tls: reserved ExportKeyingMaterial label: %s", label)
		}

		seedLen := len(serverRandom) + len(clientRandom)
		if context != nil {
			seedLen += 2 + len(context)
		}
		seed := make([]byte, 0, seedLen)

		seed = append(seed, clientRandom...)
		seed = append(seed, serverRandom...)

		if context != nil {
			if len(context) >= 1<<16 {
				return nil, fmt.Errorf("crypto/tls: ExportKeyingMaterial context too long")
			}
			seed = append(seed, byte(len(context)>>8), byte(len(context)))
			seed = append(seed, context...)
		}

		keyMaterial := make([]byte, length)
		prfForVersion(version, suite)(keyMaterial, masterSecret, []byte(label), seed)
		return keyMaterial, nil
	}
}