spicetools/util/rc4.cpp

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2024-08-28 15:10:34 +00:00
#include "rc4.h"
#include <iterator>
#include "util/logging.h"
util::RC4::RC4(uint8_t *key, size_t key_size) {
// initialize S-BOX
for (size_t i = 0; i < std::size(s_box); i++)
s_box[i] = (uint8_t) i;
// check key size
if (!key_size)
return;
// KSA
size_t j = 0;
for (size_t i = 0; i < std::size(s_box); i++) {
// update
j = (j + s_box[i] + key[i % key_size]) % std::size(s_box);
// swap
auto tmp = s_box[i];
s_box[i] = s_box[j];
s_box[j] = tmp;
}
}
void util::RC4::crypt(uint8_t *data, size_t size) {
// iterate all bytes
for (size_t pos = 0; pos < size; pos++) {
// update
a = (a + 1) % std::size(s_box);
b = (b + s_box[a]) % std::size(s_box);
// swap
auto tmp = s_box[a];
s_box[a] = s_box[b];
s_box[b] = tmp;
// crypt
data[pos] ^= s_box[(s_box[a] + s_box[b]) % std::size(s_box)];
}
}