82 lines
2.1 KiB
C++
82 lines
2.1 KiB
C++
/*
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* Copyright (c) 2023 Stephen Heumann
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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#include "rc4.h"
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/*
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* Initialize an RC4 context context with a specified key.
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* This must be called before calling rc4_process.
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*/
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void rc4_init(struct rc4_context *context,
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const unsigned char *key,
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unsigned keylength)
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{
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unsigned int i;
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unsigned char j;
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unsigned char temp;
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for (i = 0; i < 256; i++) {
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context->S[i] = i;
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}
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j = 0;
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for (i = 0; i < 256; i++) {
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j = j + context->S[i] + key[i % keylength];
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temp = context->S[j];
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context->S[j] = context->S[i];
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context->S[i] = temp;
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}
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context->i = 0;
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context->j = 0;
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}
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/*
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* Process data using RC4. This either encrypts or decrypts data,
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* depending on whether in contains plaintext or ciphertext.
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*
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* To get the raw RC4 output stream, specify the input as all zeros.
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* The same buffer may be used for in and out.
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*/
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void rc4_process(struct rc4_context *context,
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const unsigned char *in,
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unsigned char *out,
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unsigned long length)
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{
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extern unsigned char RC4_PRGA(void);
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while (length--) {
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asm {
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phd
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lda context
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tcd
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sep #0x30
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jsl RC4_PRGA
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pld
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eor [in]
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sta [out]
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rep #0x30
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}
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in++;
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out++;
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}
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}
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#append "rc4.asm"
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