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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package chacha20poly1305
import (
"encoding/binary"
"golang.org/x/crypto/chacha20"
"golang.org/x/crypto/internal/subtle"
"golang.org/x/crypto/poly1305"
)
func roundTo16(n int) int {
return 16 * ((n + 15) / 16)
}
func (c *chacha20poly1305) sealGeneric(dst, nonce, plaintext, additionalData []byte) []byte {
ret, out := sliceForAppend(dst, len(plaintext)+poly1305.TagSize)
if subtle.InexactOverlap(out, plaintext) {
panic("chacha20poly1305: invalid buffer overlap")
}
var polyKey, discardBuf [32]byte
s, _ := chacha20.NewUnauthenticatedCipher(c.key[:], nonce)
s.XORKeyStream(polyKey[:], polyKey[:])
s.XORKeyStream(discardBuf[:], discardBuf[:]) // skip the next 32 bytes
s.XORKeyStream(out, plaintext)
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
}
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 polyKey, discardBuf [32]byte
s, _ := chacha20.NewUnauthenticatedCipher(c.key[:], nonce)
s.XORKeyStream(polyKey[:], polyKey[:])
s.XORKeyStream(discardBuf[:], discardBuf[:]) // skip the next 32 bytes
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 subtle.InexactOverlap(out, ciphertext) {
panic("chacha20poly1305: invalid buffer overlap")
}
if !poly1305.Verify(&tag, polyInput, &polyKey) {
for i := range out {
out[i] = 0
}
return nil, errOpen
}
s.XORKeyStream(out, ciphertext)
return ret, nil
}
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