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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/internal/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 [32]byte
- s := chacha20.New(c.key, [3]uint32{
- binary.LittleEndian.Uint32(nonce[0:4]),
- binary.LittleEndian.Uint32(nonce[4:8]),
- binary.LittleEndian.Uint32(nonce[8:12]),
- })
- s.XORKeyStream(polyKey[:], polyKey[:])
- s.Advance() // 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 [32]byte
- s := chacha20.New(c.key, [3]uint32{
- binary.LittleEndian.Uint32(nonce[0:4]),
- binary.LittleEndian.Uint32(nonce[4:8]),
- binary.LittleEndian.Uint32(nonce[8:12]),
- })
- s.XORKeyStream(polyKey[:], polyKey[:])
- s.Advance() // 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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