// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Cryptographic API
 *
 * ARC4 Cipher Algorithm
 *
 * Jon Oberheide <jon@oberheide.org>
 */

#include <crypto/arc4.h>
#include <linux/export.h>
#include <linux/module.h>

int arc4_setkey(struct arc4_ctx *ctx, const u8 *in_key, unsigned int key_len)
{
        int i, j = 0, k = 0;

        ctx->x = 1;
        ctx->y = 0;

        for (i = 0; i < 256; i++)
                ctx->S[i] = i;

        for (i = 0; i < 256; i++) {
                u32 a = ctx->S[i];

                j = (j + in_key[k] + a) & 0xff;
                ctx->S[i] = ctx->S[j];
                ctx->S[j] = a;
                if (++k >= key_len)
                        k = 0;
        }

        return 0;
}
EXPORT_SYMBOL(arc4_setkey);

void arc4_crypt(struct arc4_ctx *ctx, u8 *out, const u8 *in, unsigned int len)
{
        u32 *const S = ctx->S;
        u32 x, y, a, b;
        u32 ty, ta, tb;

        if (len == 0)
                return;

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

        a = S[x];
        y = (y + a) & 0xff;
        b = S[y];

        do {
                S[y] = a;
                a = (a + b) & 0xff;
                S[x] = b;
                x = (x + 1) & 0xff;
                ta = S[x];
                ty = (y + ta) & 0xff;
                tb = S[ty];
                *out++ = *in++ ^ S[a];
                if (--len == 0)
                        break;
                y = ty;
                a = ta;
                b = tb;
        } while (true);

        ctx->x = x;
        ctx->y = y;
}
EXPORT_SYMBOL(arc4_crypt);

MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
MODULE_LICENSE("GPL");