library/arc4.c

/*
 *  An implementation of the ARCFOUR algorithm
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
 */
/*
 *  The ARCFOUR algorithm was publicly disclosed on 94/09.
 *
 *  http://groups.google.com/group/sci.crypt/msg/10a300c9d21afca0
 */

#include "common.h"

#if defined(MBEDTLS_ARC4_C)

#include "mbedtls/arc4.h"
#include "mbedtls/platform_util.h"

#include <string.h>

#include "mbedtls/platform.h"

#if !defined(MBEDTLS_ARC4_ALT)

void mbedtls_arc4_init(mbedtls_arc4_context *ctx)
{
    memset(ctx, 0, sizeof(mbedtls_arc4_context));
}

void mbedtls_arc4_free(mbedtls_arc4_context *ctx)
{
    if (ctx == NULL) {
        return;
    }

    mbedtls_platform_zeroize(ctx, sizeof(mbedtls_arc4_context));
}

/*
 * ARC4 key schedule
 */
void mbedtls_arc4_setup(mbedtls_arc4_context *ctx, const unsigned char *key,
                        unsigned int keylen)
{
    int i, j, a;
    unsigned int k;
    unsigned char *m;

    ctx->x = 0;
    ctx->y = 0;
    m = ctx->m;

    for (i = 0; i < 256; i++) {
        m[i] = (unsigned char) i;
    }

    j = k = 0;

    for (i = 0; i < 256; i++, k++) {
        if (k >= keylen) {
            k = 0;
        }

        a = m[i];
        j = (j + a + key[k]) & 0xFF;
        m[i] = m[j];
        m[j] = (unsigned char) a;
    }
}

/*
 * ARC4 cipher function
 */
int mbedtls_arc4_crypt(mbedtls_arc4_context *ctx, size_t length, const unsigned char *input,
                       unsigned char *output)
{
    int x, y, a, b;
    size_t i;
    unsigned char *m;

    x = ctx->x;
    y = ctx->y;
    m = ctx->m;

    for (i = 0; i < length; i++) {
        x = (x + 1) & 0xFF; a = m[x];
        y = (y + a) & 0xFF; b = m[y];

        m[x] = (unsigned char) b;
        m[y] = (unsigned char) a;

        output[i] = (unsigned char)
                    (input[i] ^ m[(unsigned char) (a + b)]);
    }

    ctx->x = x;
    ctx->y = y;

    return 0;
}

#endif /* !MBEDTLS_ARC4_ALT */

#if defined(MBEDTLS_SELF_TEST)
/*
 * ARC4 tests vectors as posted by Eric Rescorla in sep. 1994:
 *
 * http://groups.google.com/group/comp.security.misc/msg/10a300c9d21afca0
 */
static const unsigned char arc4_test_key[3][8] =
{
    { 0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF },
    { 0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF },
    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }
};

static const unsigned char arc4_test_pt[3][8] =
{
    { 0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF },
    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
    { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }
};

static const unsigned char arc4_test_ct[3][8] =
{
    { 0x75, 0xB7, 0x87, 0x80, 0x99, 0xE0, 0xC5, 0x96 },
    { 0x74, 0x94, 0xC2, 0xE7, 0x10, 0x4B, 0x08, 0x79 },
    { 0xDE, 0x18, 0x89, 0x41, 0xA3, 0x37, 0x5D, 0x3A }
};

/*
 * Checkup routine
 */
int mbedtls_arc4_self_test(int verbose)
{
    int i, ret = 0;
    unsigned char ibuf[8];
    unsigned char obuf[8];
    mbedtls_arc4_context ctx;

    mbedtls_arc4_init(&ctx);

    for (i = 0; i < 3; i++) {
        if (verbose != 0) {
            mbedtls_printf("  ARC4 test #%d: ", i + 1);
        }

        memcpy(ibuf, arc4_test_pt[i], 8);

        mbedtls_arc4_setup(&ctx, arc4_test_key[i], 8);
        mbedtls_arc4_crypt(&ctx, 8, ibuf, obuf);

        if (memcmp(obuf, arc4_test_ct[i], 8) != 0) {
            if (verbose != 0) {
                mbedtls_printf("failed\n");
            }

            ret = 1;
            goto exit;
        }

        if (verbose != 0) {
            mbedtls_printf("passed\n");
        }
    }

    if (verbose != 0) {
        mbedtls_printf("\n");
    }

exit:
    mbedtls_arc4_free(&ctx);

    return ret;
}

#endif /* MBEDTLS_SELF_TEST */

#endif /* MBEDTLS_ARC4_C */