87 lines
2.5 KiB
Go
87 lines
2.5 KiB
Go
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// Copyright 2018 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
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import (
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"crypto/cipher"
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"errors"
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"golang.org/x/crypto/chacha20"
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)
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type xchacha20poly1305 struct {
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key [KeySize]byte
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}
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// NewX returns a XChaCha20-Poly1305 AEAD that uses the given 256-bit key.
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//
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// XChaCha20-Poly1305 is a ChaCha20-Poly1305 variant that takes a longer nonce,
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// suitable to be generated randomly without risk of collisions. It should be
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// preferred when nonce uniqueness cannot be trivially ensured, or whenever
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// nonces are randomly generated.
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func NewX(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(xchacha20poly1305)
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copy(ret.key[:], key)
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return ret, nil
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}
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func (*xchacha20poly1305) NonceSize() int {
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return NonceSizeX
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}
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func (*xchacha20poly1305) Overhead() int {
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return 16
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}
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func (x *xchacha20poly1305) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
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if len(nonce) != NonceSizeX {
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panic("chacha20poly1305: bad nonce length passed to Seal")
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}
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// XChaCha20-Poly1305 technically supports a 64-bit counter, so there is no
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// size limit. However, since we reuse the ChaCha20-Poly1305 implementation,
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// the second half of the counter is not available. This is unlikely to be
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// an issue because the cipher.AEAD API requires the entire message to be in
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// memory, and the counter overflows at 256 GB.
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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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c := new(chacha20poly1305)
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hKey, _ := chacha20.HChaCha20(x.key[:], nonce[0:16])
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copy(c.key[:], hKey)
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// The first 4 bytes of the final nonce are unused counter space.
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cNonce := make([]byte, NonceSize)
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copy(cNonce[4:12], nonce[16:24])
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return c.seal(dst, cNonce[:], plaintext, additionalData)
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}
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func (x *xchacha20poly1305) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
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if len(nonce) != NonceSizeX {
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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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c := new(chacha20poly1305)
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hKey, _ := chacha20.HChaCha20(x.key[:], nonce[0:16])
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copy(c.key[:], hKey)
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// The first 4 bytes of the final nonce are unused counter space.
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cNonce := make([]byte, NonceSize)
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copy(cNonce[4:12], nonce[16:24])
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return c.open(dst, cNonce[:], ciphertext, additionalData)
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}
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