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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 implements the ChaCha20-Poly1305 AEAD as specified in RFC 7539.
package chacha20poly1305 // import "golang.org/x/crypto/chacha20poly1305"
import (
"crypto/cipher"
"encoding/binary"
"errors"
)
const (
// KeySize is the size of the key used by this AEAD, in bytes.
KeySize = 32
// NonceSize is the size of the nonce used with this AEAD, in bytes.
NonceSize = 12
)
type chacha20poly1305 struct {
key [8]uint32
}
// New returns a ChaCha20-Poly1305 AEAD that uses the given, 256-bit key.
func New(key []byte) (cipher.AEAD, error) {
if len(key) != KeySize {
return nil, errors.New("chacha20poly1305: bad key length")
}
ret := new(chacha20poly1305)
ret.key[0] = binary.LittleEndian.Uint32(key[0:4])
ret.key[1] = binary.LittleEndian.Uint32(key[4:8])
ret.key[2] = binary.LittleEndian.Uint32(key[8:12])
ret.key[3] = binary.LittleEndian.Uint32(key[12:16])
ret.key[4] = binary.LittleEndian.Uint32(key[16:20])
ret.key[5] = binary.LittleEndian.Uint32(key[20:24])
ret.key[6] = binary.LittleEndian.Uint32(key[24:28])
ret.key[7] = binary.LittleEndian.Uint32(key[28:32])
return ret, nil
}
func (c *chacha20poly1305) NonceSize() int {
return NonceSize
}
func (c *chacha20poly1305) Overhead() int {
return 16
}
func (c *chacha20poly1305) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
if len(nonce) != NonceSize {
panic("chacha20poly1305: bad nonce length passed to Seal")
}
if uint64(len(plaintext)) > (1<<38)-64 {
panic("chacha20poly1305: plaintext too large")
}
return c.seal(dst, nonce, plaintext, additionalData)
}
var errOpen = errors.New("chacha20poly1305: message authentication failed")
func (c *chacha20poly1305) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
if len(nonce) != NonceSize {
panic("chacha20poly1305: bad nonce length passed to Open")
}
if len(ciphertext) < 16 {
return nil, errOpen
}
if uint64(len(ciphertext)) > (1<<38)-48 {
panic("chacha20poly1305: ciphertext too large")
}
return c.open(dst, nonce, ciphertext, additionalData)
}
// sliceForAppend takes a slice and a requested number of bytes. It returns a
// slice with the contents of the given slice followed by that many bytes and a
// second slice that aliases into it and contains only the extra bytes. If the
// original slice has sufficient capacity then no allocation is performed.
func sliceForAppend(in []byte, n int) (head, tail []byte) {
if total := len(in) + n; cap(in) >= total {
head = in[:total]
} else {
head = make([]byte, total)
copy(head, in)
}
tail = head[len(in):]
return
}
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