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99 lines
2.7 KiB
Go
99 lines
2.7 KiB
Go
// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package chacha20poly1305 implements the ChaCha20-Poly1305 AEAD and its
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// extended nonce variant XChaCha20-Poly1305, as specified in RFC 8439 and
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// draft-irtf-cfrg-xchacha-01.
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package chacha20poly1305
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import (
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"crypto/cipher"
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"errors"
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)
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const (
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// KeySize is the size of the key used by this AEAD, in bytes.
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KeySize = 32
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// NonceSize is the size of the nonce used with the standard variant of this
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// AEAD, in bytes.
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//
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// Note that this is too short to be safely generated at random if the same
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// key is reused more than 2³² times.
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NonceSize = 12
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// NonceSizeX is the size of the nonce used with the XChaCha20-Poly1305
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// variant of this AEAD, in bytes.
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NonceSizeX = 24
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// Overhead is the size of the Poly1305 authentication tag, and the
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// difference between a ciphertext length and its plaintext.
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Overhead = 16
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)
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type chacha20poly1305 struct {
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key [KeySize]byte
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}
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// New returns a ChaCha20-Poly1305 AEAD that uses the given 256-bit key.
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func New(key []byte) (cipher.AEAD, error) {
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if len(key) != KeySize {
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return nil, errors.New("chacha20poly1305: bad key length")
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}
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ret := new(chacha20poly1305)
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copy(ret.key[:], key)
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return ret, nil
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}
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func (c *chacha20poly1305) NonceSize() int {
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return NonceSize
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}
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func (c *chacha20poly1305) Overhead() int {
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return Overhead
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}
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func (c *chacha20poly1305) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
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if len(nonce) != NonceSize {
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panic("chacha20poly1305: bad nonce length passed to Seal")
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}
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if uint64(len(plaintext)) > (1<<38)-64 {
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panic("chacha20poly1305: plaintext too large")
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}
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return c.seal(dst, nonce, plaintext, additionalData)
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}
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var errOpen = errors.New("chacha20poly1305: message authentication failed")
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func (c *chacha20poly1305) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
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if len(nonce) != NonceSize {
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panic("chacha20poly1305: bad nonce length passed to Open")
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}
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if len(ciphertext) < 16 {
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return nil, errOpen
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}
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if uint64(len(ciphertext)) > (1<<38)-48 {
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panic("chacha20poly1305: ciphertext too large")
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}
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return c.open(dst, nonce, ciphertext, additionalData)
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}
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// sliceForAppend takes a slice and a requested number of bytes. It returns a
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// slice with the contents of the given slice followed by that many bytes and a
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// second slice that aliases into it and contains only the extra bytes. If the
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// original slice has sufficient capacity then no allocation is performed.
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func sliceForAppend(in []byte, n int) (head, tail []byte) {
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if total := len(in) + n; cap(in) >= total {
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head = in[:total]
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} else {
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head = make([]byte, total)
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copy(head, in)
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}
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tail = head[len(in):]
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return
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}
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