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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/poly1305"
"golang.org/x/crypto/internal/subtle"
)
func writeWithPadding(p *poly1305.MAC, b []byte) {
p.Write(b)
if rem := len(b) % 16; rem != 0 {
var buf [16]byte
padLen := 16 - rem
p.Write(buf[:padLen])
}
}
func writeUint64(p *poly1305.MAC, n int) {
var buf [8]byte
binary.LittleEndian.PutUint64(buf[:], uint64(n))
p.Write(buf[:])
}
func (c *chacha20poly1305) sealGeneric(dst, nonce, plaintext, additionalData []byte) []byte {
ret, out := sliceForAppend(dst, len(plaintext)+poly1305.TagSize)
ciphertext, tag := out[:len(plaintext)], out[len(plaintext):]
if subtle.InexactOverlap(out, plaintext) {
panic("chacha20poly1305: invalid buffer overlap")
}
var polyKey [32]byte
s, _ := chacha20.NewUnauthenticatedCipher(c.key[:], nonce)
s.XORKeyStream(polyKey[:], polyKey[:])
s.SetCounter(1) // set the counter to 1, skipping 32 bytes
s.XORKeyStream(ciphertext, plaintext)
p := poly1305.New(&polyKey)
writeWithPadding(p, additionalData)
writeWithPadding(p, ciphertext)
writeUint64(p, len(additionalData))
writeUint64(p, len(plaintext))
p.Sum(tag[:0])
return ret
}
func (c *chacha20poly1305) openGeneric(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
tag := ciphertext[len(ciphertext)-16:]
ciphertext = ciphertext[:len(ciphertext)-16]
var polyKey [32]byte
s, _ := chacha20.NewUnauthenticatedCipher(c.key[:], nonce)
s.XORKeyStream(polyKey[:], polyKey[:])
s.SetCounter(1) // set the counter to 1, skipping 32 bytes
p := poly1305.New(&polyKey)
writeWithPadding(p, additionalData)
writeWithPadding(p, ciphertext)
writeUint64(p, len(additionalData))
writeUint64(p, len(ciphertext))
ret, out := sliceForAppend(dst, len(ciphertext))
if subtle.InexactOverlap(out, ciphertext) {
panic("chacha20poly1305: invalid buffer overlap")
}
if !p.Verify(tag) {
for i := range out {
out[i] = 0
}
return nil, errOpen
}
s.XORKeyStream(out, ciphertext)
return ret, nil
}
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