func (c *chacha20poly1305) openGeneric(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) { var tag [poly1305.TagSize]byte copy(tag[:], ciphertext[len(ciphertext)-16:]) ciphertext = ciphertext[:len(ciphertext)-16] var counter [16]byte copy(counter[4:], nonce) var polyKey [32]byte chacha20.XORKeyStream(polyKey[:], polyKey[:], &counter, &c.key) polyInput := make([]byte, roundTo16(len(additionalData))+roundTo16(len(ciphertext))+8+8) copy(polyInput, additionalData) copy(polyInput[roundTo16(len(additionalData)):], ciphertext) binary.LittleEndian.PutUint64(polyInput[len(polyInput)-16:], uint64(len(additionalData))) binary.LittleEndian.PutUint64(polyInput[len(polyInput)-8:], uint64(len(ciphertext))) ret, out := sliceForAppend(dst, len(ciphertext)) if !poly1305.Verify(&tag, polyInput, &polyKey) { for i := range out { out[i] = 0 } return nil, errOpen } counter[0] = 1 chacha20.XORKeyStream(out, ciphertext, &counter, &c.key) return ret, nil }
func (c *chacha20poly1305) sealGeneric(dst, nonce, plaintext, additionalData []byte) []byte { var counter [16]byte copy(counter[4:], nonce) var polyKey [32]byte chacha20.XORKeyStream(polyKey[:], polyKey[:], &counter, &c.key) ret, out := sliceForAppend(dst, len(plaintext)+poly1305.TagSize) counter[0] = 1 chacha20.XORKeyStream(out, plaintext, &counter, &c.key) polyInput := make([]byte, roundTo16(len(additionalData))+roundTo16(len(plaintext))+8+8) copy(polyInput, additionalData) copy(polyInput[roundTo16(len(additionalData)):], out[:len(plaintext)]) binary.LittleEndian.PutUint64(polyInput[len(polyInput)-16:], uint64(len(additionalData))) binary.LittleEndian.PutUint64(polyInput[len(polyInput)-8:], uint64(len(plaintext))) var tag [poly1305.TagSize]byte poly1305.Sum(&tag, polyInput, &polyKey) copy(out[len(plaintext):], tag[:]) return ret }