libqpdf/RC4_native.cc


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#include <qpdf/RC4_native.hh>

#include <qpdf/QIntC.hh>

#include <string.h>

static void
swap_byte(unsigned char& a, unsigned char& b)
{
    unsigned char t;

    t = a;
    a = b;
    b = t;
}

RC4_native::RC4_native(unsigned char const* key_data, int key_len)
{
    if (key_len == -1) {
        key_len = QIntC::to_int(strlen(reinterpret_cast<char const*>(key_data)));
    }

    for (int i = 0; i < 256; ++i) {
        key.state[i] = static_cast<unsigned char>(i);
    }
    key.x = 0;
    key.y = 0;

    int i1 = 0;
    int i2 = 0;
    for (int i = 0; i < 256; ++i) {
        i2 = (key_data[i1] + key.state[i] + i2) % 256;
        swap_byte(key.state[i], key.state[i2]);
        i1 = (i1 + 1) % key_len;
    }
}

void
RC4_native::process(unsigned char const* in_data, size_t len, unsigned char* out_data)
{
    for (size_t i = 0; i < len; ++i) {
        key.x = static_cast<unsigned char>((key.x + 1) % 256);
        key.y = static_cast<unsigned char>((key.state[key.x] + key.y) % 256);
        swap_byte(key.state[key.x], key.state[key.y]);
        int xor_index = (key.state[key.x] + key.state[key.y]) % 256;
        out_data[i] = in_data[i] ^ key.state[xor_index];
    }
}