code: func VerifyAndDecrypt(tok []byte, ttl time.Duration, k []*Key) (msg []byte) {
  	b := make([]byte, encoding.DecodedLen(len(tok)))
  	n, _ := encoding.Decode(b, tok)
  	for _, k1 := range k {
  		msg = verify(nil, b[:n], ttl, time.Now(), k1)
  		if msg != nil {
  			return msg
  		}
  	}
  	return nil
  }
docs: // VerifyAndDecrypt verifies that tok is a valid fernet token that was signed
  // with a key in k at most ttl time ago only if ttl is greater than zero.
  // Returns the message contained in tok if tok is valid, otherwise nil.