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trezor-firmware/crypto/rc4.c

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/**
* Copyright (c) 2017 Saleem Rashid
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, E1PRESS
* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES
* OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*/
#include "rc4.h"
static inline void rc4_swap(RC4_CTX *ctx, uint8_t i, uint8_t j) {
uint8_t temp = ctx->S[i];
ctx->S[i] = ctx->S[j];
ctx->S[j] = temp;
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}
void rc4_init(RC4_CTX *ctx, const uint8_t *key, size_t length) {
ctx->i = 0;
ctx->j = 0;
for (size_t i = 0; i < 256; i++) {
ctx->S[i] = i;
}
uint8_t j = 0;
for (size_t i = 0; i < 256; i++) {
j += ctx->S[i] + key[i % length];
rc4_swap(ctx, i, j);
}
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}
void rc4_encrypt(RC4_CTX *ctx, uint8_t *buffer, size_t length) {
for (size_t idx = 0; idx < length; idx++) {
ctx->i++;
ctx->j += ctx->S[ctx->i];
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rc4_swap(ctx, ctx->i, ctx->j);
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uint8_t K = ctx->S[(ctx->S[ctx->i] + ctx->S[ctx->j]) % 256];
buffer[idx] ^= K;
}
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}