Function hkdfExpand

credentials/alts/internal/conn/aeadrekey.go:126–131

hkdfExpand computes the first 16 bytes of the HKDF-expand function defined in RFC5869.

(key, info []byte)

// hkdfExpand computes the first 16 bytes of the HKDF-expand function
// defined in RFC5869.
func hkdfExpand(key, info []byte) []byte {
	mac := hmac.New(sha256.New, key)
	mac.Write(info)
	mac.Write([]byte{0x01}[:])
	return mac.Sum(nil)[:aeadKeyLen]
}