// opad = 0x5c byte repeated for key length // hmac = H([key ^ opad] H([key ^ ipad] text)) // marshalable is the combination of encoding.BinaryMarshaler and // encoding.BinaryUnmarshaler. Their method definitions are repeated here to // avoid a dependency on the encoding package. type marshalable interface { MarshalBinary() ([]byte, error) UnmarshalBinary([]byte) error } type HMAC struct { // opad and ipad may share underlying storage with HMAC clones. opad, ipad []byte outer, inner hash.Hash //...