84 lines
1.9 KiB
Go
84 lines
1.9 KiB
Go
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// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
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// Use of this source code is governed by an MIT license
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// that can be found in the LICENSE file.
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// Package rc4 implements RC4 encryption, as defined in Bruce Schneier's
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// Applied Cryptography.
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//
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// RC4 is cryptographically broken and should not be used for secure
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// applications.
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// Adapted from: https://github.com/golang/go/blob/master/src/crypto/rc4
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module rc4
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import crypto.internal.subtle
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// A Cipher is an instance of RC4 using a particular key.
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struct Cipher {
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mut:
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s []u32
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i u8
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j u8
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}
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// new_cipher creates and returns a new Cipher. The key argument should be the
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// RC4 key, at least 1 byte and at most 256 bytes.
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pub fn new_cipher(key []byte) ?Cipher {
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if key.len < 1 || key.len > 256 {
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return error('crypto.rc4: invalid key size ' + key.len.str())
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}
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mut c := Cipher{
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s: [u32(0); 256]
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}
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for i := 0; i < 256; i++ {
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c.s[i] = u32(i)
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}
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mut j := u8(0)
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for i := 0; i < 256; i++ {
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j += u8(c.s[i]) + u8(key[i%key.len])
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tmp := c.s[i]
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c.s[i] = c.s[j]
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c.s[j] = tmp
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}
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return c
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}
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// reset zeros the key data and makes the Cipher unusable.
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//
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// Deprecated: Reset can't guarantee that the key will be entirely removed from
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// the process's memory.
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pub fn (c &Cipher) reset() {
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for i in c.s {
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c.s[i] = u32(0)
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}
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c.i = u8(0)
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c.j = u8(0)
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}
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// xor_key_stream sets dst to the result of XORing src with the key stream.
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// Dst and src must overlap entirely or not at all.
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pub fn (c &Cipher) xor_key_stream(dst, src []byte) {
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if src.len == 0 {
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return
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}
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if subtle.inexact_overlap(dst.left(src.len), src) {
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panic('crypto.rc4: invalid buffer overlap')
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}
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mut i := c.i
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mut j := c.j
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_ := dst[src.len-1]
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dst = dst.left(src.len) // eliminate bounds check from loop
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for k, v in src {
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i += u8(1)
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x := c.s[i]
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j += u8(x)
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y := c.s[j]
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c.s[i] = y
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c.s[j] = x
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dst[k] = v ^ byte(c.s[u8(x+y)])
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}
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c.i = i
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c.j = j
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}
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