/* XTS: as defined in IEEE1619/D16
 *      http://grouper.ieee.org/groups/1619/email/pdf00086.pdf
 *      (sector sizes which are not a multiple of 16 bytes are,
 *      however currently unsupported)
 *
 * Copyright (c) 2007 Rik Snel <rsnel@cube.dyndns.org>
 *
 * Based om ecb.c
 * Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 */
#include <crypto/algapi.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>

#include <crypto/b128ops.h>
#include <crypto/gf128mul.h>

struct priv {
        struct crypto_cipher *child;
        struct crypto_cipher *tweak;
};

static int setkey(struct crypto_tfm *parent, const u8 *key,
                  unsigned int keylen)
{
        struct priv *ctx = crypto_tfm_ctx(parent);
        struct crypto_cipher *child = ctx->tweak;
        u32 *flags = &parent->crt_flags;
        int err;

        /* key consists of keys of equal size concatenated, therefore
         * the length must be even */
        if (keylen % 2) {
                /* tell the user why there was an error */
                *flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
                return -EINVAL;
        }

        /* we need two cipher instances: one to compute the inital 'tweak'
         * by encrypting the IV (usually the 'plain' iv) and the other
         * one to encrypt and decrypt the data */

        /* tweak cipher, uses Key2 i.e. the second half of *key */
        crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
        crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
                                       CRYPTO_TFM_REQ_MASK);
        err = crypto_cipher_setkey(child, key + keylen/2, keylen/2);
        if (err)
                return err;

        crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
                                     CRYPTO_TFM_RES_MASK);

        child = ctx->child;

        /* data cipher, uses Key1 i.e. the first half of *key */
        crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
        crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
                                       CRYPTO_TFM_REQ_MASK);
        err = crypto_cipher_setkey(child, key, keylen/2);
        if (err)
                return err;

        crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
                                     CRYPTO_TFM_RES_MASK);

        return 0;
}

struct sinfo {
        be128 t;
        struct crypto_tfm *tfm;
        void (*fn)(struct crypto_tfm *, u8 *, const u8 *);
};

static inline void xts_round(struct sinfo *s, void *dst, const void *src)
{
        be128_xor(dst, &s->t, src);             /* PP <- T xor P */
        s->fn(s->tfm, dst, dst);                /* CC <- E(Key1,PP) */
        be128_xor(dst, dst, &s->t);             /* C <- T xor CC */
}

static int crypt(struct blkcipher_desc *d,
                 struct blkcipher_walk *w, struct priv *ctx,
                 void (*tw)(struct crypto_tfm *, u8 *, const u8 *),
                 void (*fn)(struct crypto_tfm *, u8 *, const u8 *))
{
        int err;
        unsigned int avail;
        const int bs = crypto_cipher_blocksize(ctx->child);
        struct sinfo s = {
                .tfm = crypto_cipher_tfm(ctx->child),
                .fn = fn
        };
        be128 *iv;
        u8 *wsrc;
        u8 *wdst;

        err = blkcipher_walk_virt(d, w);
        if (!w->nbytes)
                return err;

        avail = w->nbytes;

        wsrc = w->src.virt.addr;
        wdst = w->dst.virt.addr;

        /* calculate first value of T */
        iv = (be128 *)w->iv;
        tw(crypto_cipher_tfm(ctx->tweak), (void *)&s.t, w->iv);

        goto first;

        for (;;) {
                do {
                        gf128mul_x_ble(&s.t, &s.t);

first:
                        xts_round(&s, wdst, wsrc);

                        wsrc += bs;
                        wdst += bs;
                } while ((avail -= bs) >= bs);

                err = blkcipher_walk_done(d, w, avail);
                if (!w->nbytes)
                        break;

                avail = w->nbytes;

                wsrc = w->src.virt.addr;
                wdst = w->dst.virt.addr;
        }

        return err;
}

static int encrypt(struct blkcipher_desc *desc, struct scatterlist *dst,
                   struct scatterlist *src, unsigned int nbytes)
{
        struct priv *ctx = crypto_blkcipher_ctx(desc->tfm);
        struct blkcipher_walk w;

        blkcipher_walk_init(&w, dst, src, nbytes);
        return crypt(desc, &w, ctx, crypto_cipher_alg(ctx->tweak)->cia_encrypt,
                     crypto_cipher_alg(ctx->child)->cia_encrypt);
}

static int decrypt(struct blkcipher_desc *desc, struct scatterlist *dst,
                   struct scatterlist *src, unsigned int nbytes)
{
        struct priv *ctx = crypto_blkcipher_ctx(desc->tfm);
        struct blkcipher_walk w;

        blkcipher_walk_init(&w, dst, src, nbytes);
        return crypt(desc, &w, ctx, crypto_cipher_alg(ctx->tweak)->cia_encrypt,
                     crypto_cipher_alg(ctx->child)->cia_decrypt);
}

static int init_tfm(struct crypto_tfm *tfm)
{
        struct crypto_cipher *cipher;
        struct crypto_instance *inst = (void *)tfm->__crt_alg;
        struct crypto_spawn *spawn = crypto_instance_ctx(inst);
        struct priv *ctx = crypto_tfm_ctx(tfm);
        u32 *flags = &tfm->crt_flags;

        cipher = crypto_spawn_cipher(spawn);
        if (IS_ERR(cipher))
                return PTR_ERR(cipher);

        if (crypto_cipher_blocksize(cipher) != 16) {
                *flags |= CRYPTO_TFM_RES_BAD_BLOCK_LEN;
                crypto_free_cipher(cipher);
                return -EINVAL;
        }

        ctx->child = cipher;

        cipher = crypto_spawn_cipher(spawn);
        if (IS_ERR(cipher)) {
                crypto_free_cipher(ctx->child);
                return PTR_ERR(cipher);
        }

        /* this check isn't really needed, leave it here just in case */
        if (crypto_cipher_blocksize(cipher) != 16) {
                crypto_free_cipher(cipher);
                crypto_free_cipher(ctx->child);
                *flags |= CRYPTO_TFM_RES_BAD_BLOCK_LEN;
                return -EINVAL;
        }

        ctx->tweak = cipher;

        return 0;
}

static void exit_tfm(struct crypto_tfm *tfm)
{
        struct priv *ctx = crypto_tfm_ctx(tfm);
        crypto_free_cipher(ctx->child);
        crypto_free_cipher(ctx->tweak);
}

static struct crypto_instance *alloc(struct rtattr **tb)
{
        struct crypto_instance *inst;
        struct crypto_alg *alg;
        int err;

        err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
        if (err)
                return ERR_PTR(err);

        alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
                                  CRYPTO_ALG_TYPE_MASK);
        if (IS_ERR(alg))
                return ERR_PTR(PTR_ERR(alg));

        inst = crypto_alloc_instance("xts", alg);
        if (IS_ERR(inst))
                goto out_put_alg;

        inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
        inst->alg.cra_priority = alg->cra_priority;
        inst->alg.cra_blocksize = alg->cra_blocksize;

        if (alg->cra_alignmask < 7)
                inst->alg.cra_alignmask = 7;
        else
                inst->alg.cra_alignmask = alg->cra_alignmask;

        inst->alg.cra_type = &crypto_blkcipher_type;

        inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize;
        inst->alg.cra_blkcipher.min_keysize =
                2 * alg->cra_cipher.cia_min_keysize;
        inst->alg.cra_blkcipher.max_keysize =
                2 * alg->cra_cipher.cia_max_keysize;

        inst->alg.cra_ctxsize = sizeof(struct priv);

        inst->alg.cra_init = init_tfm;
        inst->alg.cra_exit = exit_tfm;

        inst->alg.cra_blkcipher.setkey = setkey;
        inst->alg.cra_blkcipher.encrypt = encrypt;
        inst->alg.cra_blkcipher.decrypt = decrypt;

out_put_alg:
        crypto_mod_put(alg);
        return inst;
}

static void free(struct crypto_instance *inst)
{
        crypto_drop_spawn(crypto_instance_ctx(inst));
        kfree(inst);
}

static struct crypto_template crypto_tmpl = {
        .name = "xts",
        .alloc = alloc,
        .free = free,
        .module = THIS_MODULE,
};

static int __init crypto_module_init(void)
{
        return crypto_register_template(&crypto_tmpl);
}

static void __exit crypto_module_exit(void)
{
        crypto_unregister_template(&crypto_tmpl);
}

module_init(crypto_module_init);
module_exit(crypto_module_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("XTS block cipher mode");