/*
 * Copyright (C) 2008, Damien Miller
 * Copyright (C) 2011, Alex Hornung
 *
 * Permission to use, copy, and modify this software with or without fee
 * is hereby granted, provided that this entire notice is included in
 * all copies of any software which is or includes a copy or
 * modification of this software.
 * You may use this code under the GNU public license if you so wish. Please
 * contribute changes back to the authors under this freer than GPL license
 * so that we may further the use of strong encryption without limitations to
 * all.
 *
 * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTY. IN PARTICULAR, NONE OF THE AUTHORS MAKES ANY
 * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE
 * MERCHANTABILITY OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR
 * PURPOSE.
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <inttypes.h>

#include "tcplay.h"
#include "generic_xts.h"



static int
xts_reinit(struct xts_ctx *ctx, u_int64_t blocknum)
{
        u_int i;

        /*
         * Prepare tweak as E_k2(IV). IV is specified as LE representation
         * of a 64-bit block number which we allow to be passed in directly.
         */
        for (i = 0; i < XTS_IVSIZE; i++) {
                ctx->tweak[i] = blocknum & 0xff;
                blocknum >>= 8;
        }
        /* Last 64 bits of IV are always zero */
        bzero(ctx->tweak + XTS_IVSIZE, XTS_IVSIZE);

        return ctx->encrypt_fn(ctx->ctx2, ctx->blk_sz, ctx->tweak, ctx->tweak);
}

static int
xts_crypt(struct xts_ctx *ctx, u_int8_t *data, u_int do_encrypt)
{
        u_int8_t block[XTS_MAX_BLOCKSIZE];
        u_int i, carry_in, carry_out;
        int err;

        for (i = 0; i < ctx->blk_sz; i++)
                block[i] = data[i] ^ ctx->tweak[i];

        if (do_encrypt)
                err = ctx->encrypt_fn(ctx->ctx1, ctx->blk_sz, block, data);
        else
                err = ctx->decrypt_fn(ctx->ctx1, ctx->blk_sz, block, data);

        if (err)
                goto out;

        for (i = 0; i < ctx->blk_sz; i++)
                data[i] ^= ctx->tweak[i];

        /* Exponentiate tweak */
        carry_in = 0;
        for (i = 0; i < ctx->blk_sz; i++) {
                carry_out = ctx->tweak[i] & 0x80;
                ctx->tweak[i] = (ctx->tweak[i] << 1) | (carry_in ? 1 : 0);
                carry_in = carry_out;
        }
        if (carry_in)
                ctx->tweak[0] ^= XTS_ALPHA;

out:
        bzero(block, sizeof(block));
        return err;
}

int
xts_init(struct xts_ctx *ctx, void *arg1, void *arg2, set_key_fn _set_key_fn,
    zero_key_fn _zero_key_fn, encrypt_decrypt_fn _encrypt_fn,
    encrypt_decrypt_fn _decrypt_fn, u_int blk_sz, u_int8_t *key, int len)
{
        int err;

        if (len != 32 && len != 64)
                return -1;

        ctx->blk_sz = blk_sz;
        ctx->encrypt_fn = _encrypt_fn;
        ctx->decrypt_fn = _decrypt_fn;
        ctx->set_key_fn = _set_key_fn;
        ctx->zero_key_fn = _zero_key_fn;

        err = ctx->set_key_fn(&ctx->ctx1, arg1, arg2, key, len * 4);
        if (err)
                return -1;

        err = ctx->set_key_fn(&ctx->ctx2, arg1, arg2, key + (len / 2),
            len * 4);
        if (err) {
                ctx->zero_key_fn(&ctx->ctx1);
                return -1;
        }

        return 0;
}

int
xts_encrypt(struct xts_ctx *ctx, u_int8_t *data, size_t len, uint8_t *iv)
{
        uint64_t sector = *((uint64_t *)iv);
        int err;

        if ((len % ctx->blk_sz) != 0)
                return -1;

        err = xts_reinit(ctx, sector);
        if (err)
                return err;

        while (len > 0) {
                err = xts_crypt(ctx, data, 1);
                if (err)
                        return -1;

                data += ctx->blk_sz;
                len -= ctx->blk_sz;
        }

        return err;
}

int
xts_decrypt(struct xts_ctx *ctx, u_int8_t *data, size_t len, uint8_t *iv)
{
        uint64_t sector = *((uint64_t *)iv);
        int err;

        if ((len % ctx->blk_sz) != 0)
                return -1;

        err = xts_reinit(ctx, sector);
        if (err)
                return err;

        while (len > 0) {
                err = xts_crypt(ctx, data, 0);
                if (err)
                        return -1;

                data += ctx->blk_sz;
                len -= ctx->blk_sz;
        }

        return err;
}

int
xts_uninit(struct xts_ctx *ctx)
{
        ctx->zero_key_fn(&ctx->ctx1);
        ctx->zero_key_fn(&ctx->ctx2);

        return 0;
}