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50 lines
1.4 KiB
C
50 lines
1.4 KiB
C
/*
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* QEMU RC4 Implementation
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*
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* Copyright (c) 2020 Mike Davis
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* Copyright (c) 2024 Ryan Wendland
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include "rc4.h"
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static void rc4_swap(RC4Context *ctx, int first, int second)
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{
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uint8_t temp = ctx->s[first];
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ctx->s[first] = ctx->s[second];
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ctx->s[second] = temp;
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}
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void rc4_init(RC4Context *ctx, uint8_t *data, size_t len)
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{
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for (int i = 0; i < 256; i++) {
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ctx->s[i] = i;
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}
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for (int i = 0, j = 0; i < 256; i++) {
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j = (j + ctx->s[i] + data[i % len]) % 256;
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rc4_swap(ctx, i, j);
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}
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}
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void rc4_crypt(RC4Context *ctx, uint8_t *data, size_t len)
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{
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for (int i = 0, j = 0, k = 0; k < len; k++) {
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i = (i + 1) % 256;
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j = (j + ctx->s[i]) % 256;
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rc4_swap(ctx, i, j);
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data[k] ^= ctx->s[(ctx->s[i] + ctx->s[j]) % 256];
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}
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}
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