54 lines
1.9 KiB
Go
54 lines
1.9 KiB
Go
// Copyright 2012 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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/*
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Package salsa20 implements the Salsa20 stream cipher as specified in https://cr.yp.to/snuffle/spec.pdf.
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Salsa20 differs from many other stream ciphers in that it is message orientated
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rather than byte orientated. Keystream blocks are not preserved between calls,
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therefore each side must encrypt/decrypt data with the same segmentation.
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Another aspect of this difference is that part of the counter is exposed as
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a nonce in each call. Encrypting two different messages with the same (key,
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nonce) pair leads to trivial plaintext recovery. This is analogous to
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encrypting two different messages with the same key with a traditional stream
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cipher.
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This package also implements XSalsa20: a version of Salsa20 with a 24-byte
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nonce as specified in https://cr.yp.to/snuffle/xsalsa-20081128.pdf. Simply
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passing a 24-byte slice as the nonce triggers XSalsa20.
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*/
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package salsa20 // import "golang.org/x/crypto/salsa20"
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// TODO(agl): implement XORKeyStream12 and XORKeyStream8 - the reduced round variants of Salsa20.
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import (
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"golang.org/x/crypto/salsa20/salsa"
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)
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// XORKeyStream crypts bytes from in to out using the given key and nonce.
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// In and out must overlap entirely or not at all. Nonce must
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// be either 8 or 24 bytes long.
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func XORKeyStream(out, in []byte, nonce []byte, key *[32]byte) {
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if len(out) < len(in) {
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in = in[:len(out)]
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}
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var subNonce [16]byte
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if len(nonce) == 24 {
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var subKey [32]byte
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var hNonce [16]byte
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copy(hNonce[:], nonce[:16])
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salsa.HSalsa20(&subKey, &hNonce, key, &salsa.Sigma)
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copy(subNonce[:], nonce[16:])
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key = &subKey
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} else if len(nonce) == 8 {
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copy(subNonce[:], nonce[:])
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} else {
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panic("salsa20: nonce must be 8 or 24 bytes")
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}
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salsa.XORKeyStream(out, in, &subNonce, key)
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}
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