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/* 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");