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
}