forked from KolibriOS/kolibrios
48 lines
1.3 KiB
C
48 lines
1.3 KiB
C
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/*********************************************************************
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* Filename: arcfour.c
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* Author: Brad Conte (brad AT bradconte.com)
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* Copyright:
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* Disclaimer: This code is presented "as is" without any guarantees.
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* Details: Implementation of the ARCFOUR encryption algorithm.
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Algorithm specification can be found here:
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* http://en.wikipedia.org/wiki/RC4
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*********************************************************************/
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/*************************** HEADER FILES ***************************/
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#include <stdlib.h>
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#include <cryptal/arcfour.h>
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/*********************** FUNCTION DEFINITIONS ***********************/
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void arcfour_key_setup(BYTE state[], const BYTE key[], int len)
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{
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int i, j;
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BYTE t;
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for (i = 0; i < 256; ++i)
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state[i] = i;
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for (i = 0, j = 0; i < 256; ++i) {
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j = (j + state[i] + key[i % len]) % 256;
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t = state[i];
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state[i] = state[j];
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state[j] = t;
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}
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}
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// This does not hold state between calls. It always generates the
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// stream starting from the first output byte.
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void arcfour_generate_stream(BYTE state[], BYTE out[], size_t len)
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{
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int i, j;
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size_t idx;
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BYTE t;
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for (idx = 0, i = 0, j = 0; idx < len; ++idx) {
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i = (i + 1) % 256;
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j = (j + state[i]) % 256;
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t = state[i];
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state[i] = state[j];
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state[j] = t;
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out[idx] = state[(state[i] + state[j]) % 256];
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}
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}
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