cbc.c

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/*
 * CBC: Cipher Block Chaining mode
 *
 * Copyright (c) 2006 Herbert Xu <[email protected]>
 *
 * 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/log2.h>
#include <linux/module.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>

struct crypto_cbc_ctx {
    struct crypto_cipher *child;
};

static int crypto_cbc_setkey(struct crypto_tfm *parent, const u8 *key,
                 unsigned int keylen)
{
    struct crypto_cbc_ctx *ctx = crypto_tfm_ctx(parent);
    struct crypto_cipher *child = ctx->child;
    int err;

    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);
    crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
                     CRYPTO_TFM_RES_MASK);
    return err;
}

static int crypto_cbc_encrypt_segment(struct blkcipher_desc *desc,
                      struct blkcipher_walk *walk,
                      struct crypto_cipher *tfm)
{
    void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
        crypto_cipher_alg(tfm)->cia_encrypt;
    int bsize = crypto_cipher_blocksize(tfm);
    unsigned int nbytes = walk->nbytes;
    u8 *src = walk->src.virt.addr;
    u8 *dst = walk->dst.virt.addr;
    u8 *iv = walk->iv;

    do {
        crypto_xor(iv, src, bsize);
        fn(crypto_cipher_tfm(tfm), dst, iv);
        memcpy(iv, dst, bsize);

        src += bsize;
        dst += bsize;
    } while ((nbytes -= bsize) >= bsize);

    return nbytes;
}

static int crypto_cbc_encrypt_inplace(struct blkcipher_desc *desc,
                      struct blkcipher_walk *walk,
                      struct crypto_cipher *tfm)
{
    void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
        crypto_cipher_alg(tfm)->cia_encrypt;
    int bsize = crypto_cipher_blocksize(tfm);
    unsigned int nbytes = walk->nbytes;
    u8 *src = walk->src.virt.addr;
    u8 *iv = walk->iv;

    do {
        crypto_xor(src, iv, bsize);
        fn(crypto_cipher_tfm(tfm), src, src);
        iv = src;

        src += bsize;
    } while ((nbytes -= bsize) >= bsize);

    memcpy(walk->iv, iv, bsize);

    return nbytes;
}

static int crypto_cbc_encrypt(struct blkcipher_desc *desc,
                  struct scatterlist *dst, struct scatterlist *src,
                  unsigned int nbytes)
{
    struct blkcipher_walk walk;
    struct crypto_blkcipher *tfm = desc->tfm;
    struct crypto_cbc_ctx *ctx = crypto_blkcipher_ctx(tfm);
    struct crypto_cipher *child = ctx->child;
    int err;

    blkcipher_walk_init(&walk, dst, src, nbytes);
    err = blkcipher_walk_virt(desc, &walk);

    while ((nbytes = walk.nbytes)) {
        if (walk.src.virt.addr == walk.dst.virt.addr)
            nbytes = crypto_cbc_encrypt_inplace(desc, &walk, child);
        else
            nbytes = crypto_cbc_encrypt_segment(desc, &walk, child);
        err = blkcipher_walk_done(desc, &walk, nbytes);
    }

    return err;
}

static int crypto_cbc_decrypt_segment(struct blkcipher_desc *desc,
                      struct blkcipher_walk *walk,
                      struct crypto_cipher *tfm)
{
    void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
        crypto_cipher_alg(tfm)->cia_decrypt;
    int bsize = crypto_cipher_blocksize(tfm);
    unsigned int nbytes = walk->nbytes;
    u8 *src = walk->src.virt.addr;
    u8 *dst = walk->dst.virt.addr;
    u8 *iv = walk->iv;

    do {
        fn(crypto_cipher_tfm(tfm), dst, src);
        crypto_xor(dst, iv, bsize);
        iv = src;

        src += bsize;
        dst += bsize;
    } while ((nbytes -= bsize) >= bsize);

    memcpy(walk->iv, iv, bsize);

    return nbytes;
}

static int crypto_cbc_decrypt_inplace(struct blkcipher_desc *desc,
                      struct blkcipher_walk *walk,
                      struct crypto_cipher *tfm)
{
    void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
        crypto_cipher_alg(tfm)->cia_decrypt;
    int bsize = crypto_cipher_blocksize(tfm);
    unsigned int nbytes = walk->nbytes;
    u8 *src = walk->src.virt.addr;
    u8 last_iv[bsize];

    /* Start of the last block. */
    src += nbytes - (nbytes & (bsize - 1)) - bsize;
    memcpy(last_iv, src, bsize);

    for (;;) {
        fn(crypto_cipher_tfm(tfm), src, src);
        if ((nbytes -= bsize) < bsize)
            break;
        crypto_xor(src, src - bsize, bsize);
        src -= bsize;
    }

    crypto_xor(src, walk->iv, bsize);
    memcpy(walk->iv, last_iv, bsize);

    return nbytes;
}

static int crypto_cbc_decrypt(struct blkcipher_desc *desc,
                  struct scatterlist *dst, struct scatterlist *src,
                  unsigned int nbytes)
{
    struct blkcipher_walk walk;
    struct crypto_blkcipher *tfm = desc->tfm;
    struct crypto_cbc_ctx *ctx = crypto_blkcipher_ctx(tfm);
    struct crypto_cipher *child = ctx->child;
    int err;

    blkcipher_walk_init(&walk, dst, src, nbytes);
    err = blkcipher_walk_virt(desc, &walk);

    while ((nbytes = walk.nbytes)) {
        if (walk.src.virt.addr == walk.dst.virt.addr)
            nbytes = crypto_cbc_decrypt_inplace(desc, &walk, child);
        else
            nbytes = crypto_cbc_decrypt_segment(desc, &walk, child);
        err = blkcipher_walk_done(desc, &walk, nbytes);
    }

    return err;
}

static int crypto_cbc_init_tfm(struct crypto_tfm *tfm)
{
    struct crypto_instance *inst = (void *)tfm->__crt_alg;
    struct crypto_spawn *spawn = crypto_instance_ctx(inst);
    struct crypto_cbc_ctx *ctx = crypto_tfm_ctx(tfm);
    struct crypto_cipher *cipher;

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

    ctx->child = cipher;
    return 0;
}

static void crypto_cbc_exit_tfm(struct crypto_tfm *tfm)
{
    struct crypto_cbc_ctx *ctx = crypto_tfm_ctx(tfm);
    crypto_free_cipher(ctx->child);
}

static struct crypto_instance *crypto_cbc_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_CAST(alg);

    inst = ERR_PTR(-EINVAL);
    if (!is_power_of_2(alg->cra_blocksize))
        goto out_put_alg;

    inst = crypto_alloc_instance("cbc", 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;
    inst->alg.cra_alignmask = alg->cra_alignmask;
    inst->alg.cra_type = &crypto_blkcipher_type;

    /* We access the data as u32s when xoring. */
    inst->alg.cra_alignmask |= __alignof__(u32) - 1;

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

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

    inst->alg.cra_init = crypto_cbc_init_tfm;
    inst->alg.cra_exit = crypto_cbc_exit_tfm;

    inst->alg.cra_blkcipher.setkey = crypto_cbc_setkey;
    inst->alg.cra_blkcipher.encrypt = crypto_cbc_encrypt;
    inst->alg.cra_blkcipher.decrypt = crypto_cbc_decrypt;

out_put_alg:
    crypto_mod_put(alg);
    return inst;
}

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

static struct crypto_template crypto_cbc_tmpl = {
    .name = "cbc",
    .alloc = crypto_cbc_alloc,
    .free = crypto_cbc_free,
    .module = THIS_MODULE,
};

static int __init crypto_cbc_module_init(void)
{
    return crypto_register_template(&crypto_cbc_tmpl);
}

static void __exit crypto_cbc_module_exit(void)
{
    crypto_unregister_template(&crypto_cbc_tmpl);
}

module_init(crypto_cbc_module_init);
module_exit(crypto_cbc_module_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("CBC block cipher algorithm");