{ return nil, errors.New("cipher: the nonce can't have zero length") } if cipher.BlockSize() != gcmBlockSize { return nil, errors.New("cipher: NewGCM requires 128-bit block cipher") } g.cipher = *cipher g.nonceSize = nonceSize g.tagSize = tagSize initGCM(g) return g, nil } const ( gcmBlockSize = 16 gcmTagSize = 16 gcmMinimumTagSize = 12 // NIST SP 800-38D recommends tags with 12 or more bytes. gcmStandardNonceSize = 12 ) func (g *GCM) NonceSize() int { return g.nonceSize } func (g *GCM) Overhead()...