/*
 * Key Wrapping: RFC3394 / NIST SP800-38F
 *
 * Copyright (C) 2015, Stephan Mueller <smueller@chronox.de>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, and the entire permission notice in its entirety,
 *    including the disclaimer of warranties.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior
 *    written permission.
 *
 * ALTERNATIVELY, this product may be distributed under the terms of
 * the GNU General Public License, in which case the provisions of the GPL2
 * are required INSTEAD OF the above restrictions.  (This clause is
 * necessary due to a potential bad interaction between the GPL and
 * the restrictions contained in a BSD-style copyright.)
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
 * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 */

/*
 * Note for using key wrapping:
 *
 *      * The result of the encryption operation is the ciphertext starting
 *        with the 2nd semiblock. The first semiblock is provided as the IV.
 *        The IV used to start the encryption operation is the default IV.
 *
 *      * The input for the decryption is the first semiblock handed in as an
 *        IV. The ciphertext is the data starting with the 2nd semiblock. The
 *        return code of the decryption operation will be EBADMSG in case an
 *        integrity error occurs.
 *
 * To obtain the full result of an encryption as expected by SP800-38F, the
 * caller must allocate a buffer of plaintext + 8 bytes:
 *
 *      unsigned int datalen = ptlen + crypto_skcipher_ivsize(tfm);
 *      u8 data[datalen];
 *      u8 *iv = data;
 *      u8 *pt = data + crypto_skcipher_ivsize(tfm);
 *              <ensure that pt contains the plaintext of size ptlen>
 *      sg_init_one(&sg, pt, ptlen);
 *      skcipher_request_set_crypt(req, &sg, &sg, ptlen, iv);
 *
 *      ==> After encryption, data now contains full KW result as per SP800-38F.
 *
 * In case of decryption, ciphertext now already has the expected length
 * and must be segmented appropriately:
 *
 *      unsigned int datalen = CTLEN;
 *      u8 data[datalen];
 *              <ensure that data contains full ciphertext>
 *      u8 *iv = data;
 *      u8 *ct = data + crypto_skcipher_ivsize(tfm);
 *      unsigned int ctlen = datalen - crypto_skcipher_ivsize(tfm);
 *      sg_init_one(&sg, ct, ctlen);
 *      skcipher_request_set_crypt(req, &sg, &sg, ctlen, iv);
 *
 *      ==> After decryption (which hopefully does not return EBADMSG), the ct
 *      pointer now points to the plaintext of size ctlen.
 *
 * Note 2: KWP is not implemented as this would defy in-place operation.
 *         If somebody wants to wrap non-aligned data, he should simply pad
 *         the input with zeros to fill it up to the 8 byte boundary.
 */

#include <linux/module.h>
#include <linux/crypto.h>
#include <linux/scatterlist.h>
#include <crypto/scatterwalk.h>
#include <crypto/internal/cipher.h>
#include <crypto/internal/skcipher.h>

struct crypto_kw_block {
#define SEMIBSIZE 8
        __be64 A;
        __be64 R;
};

/*
 * Fast forward the SGL to the "end" length minus SEMIBSIZE.
 * The start in the SGL defined by the fast-forward is returned with
 * the walk variable
 */
static void crypto_kw_scatterlist_ff(struct scatter_walk *walk,
                                     struct scatterlist *sg,
                                     unsigned int end)
{
        unsigned int skip = 0;

        /* The caller should only operate on full SEMIBLOCKs. */
        BUG_ON(end < SEMIBSIZE);

        skip = end - SEMIBSIZE;
        while (sg) {
                if (sg->length > skip) {
                        scatterwalk_start(walk, sg);
                        scatterwalk_advance(walk, skip);
                        break;
                }

                skip -= sg->length;
                sg = sg_next(sg);
        }
}

static int crypto_kw_decrypt(struct skcipher_request *req)
{
        struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
        struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
        struct crypto_kw_block block;
        struct scatterlist *src, *dst;
        u64 t = 6 * ((req->cryptlen) >> 3);
        unsigned int i;
        int ret = 0;

        /*
         * Require at least 2 semiblocks (note, the 3rd semiblock that is
         * required by SP800-38F is the IV.
         */
        if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
                return -EINVAL;

        /* Place the IV into block A */
        memcpy(&block.A, req->iv, SEMIBSIZE);

        /*
         * src scatterlist is read-only. dst scatterlist is r/w. During the
         * first loop, src points to req->src and dst to req->dst. For any
         * subsequent round, the code operates on req->dst only.
         */
        src = req->src;
        dst = req->dst;

        for (i = 0; i < 6; i++) {
                struct scatter_walk src_walk, dst_walk;
                unsigned int nbytes = req->cryptlen;

                while (nbytes) {
                        /* move pointer by nbytes in the SGL */
                        crypto_kw_scatterlist_ff(&src_walk, src, nbytes);
                        /* get the source block */
                        scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
                                               false);

                        /* perform KW operation: modify IV with counter */
                        block.A ^= cpu_to_be64(t);
                        t--;
                        /* perform KW operation: decrypt block */
                        crypto_cipher_decrypt_one(cipher, (u8 *)&block,
                                                  (u8 *)&block);

                        /* move pointer by nbytes in the SGL */
                        crypto_kw_scatterlist_ff(&dst_walk, dst, nbytes);
                        /* Copy block->R into place */
                        scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
                                               true);

                        nbytes -= SEMIBSIZE;
                }

                /* we now start to operate on the dst SGL only */
                src = req->dst;
                dst = req->dst;
        }

        /* Perform authentication check */
        if (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL))
                ret = -EBADMSG;

        memzero_explicit(&block, sizeof(struct crypto_kw_block));

        return ret;
}

static int crypto_kw_encrypt(struct skcipher_request *req)
{
        struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
        struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
        struct crypto_kw_block block;
        struct scatterlist *src, *dst;
        u64 t = 1;
        unsigned int i;

        /*
         * Require at least 2 semiblocks (note, the 3rd semiblock that is
         * required by SP800-38F is the IV that occupies the first semiblock.
         * This means that the dst memory must be one semiblock larger than src.
         * Also ensure that the given data is aligned to semiblock.
         */
        if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
                return -EINVAL;

        /*
         * Place the predefined IV into block A -- for encrypt, the caller
         * does not need to provide an IV, but he needs to fetch the final IV.
         */
        block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL);

        /*
         * src scatterlist is read-only. dst scatterlist is r/w. During the
         * first loop, src points to req->src and dst to req->dst. For any
         * subsequent round, the code operates on req->dst only.
         */
        src = req->src;
        dst = req->dst;

        for (i = 0; i < 6; i++) {
                struct scatter_walk src_walk, dst_walk;
                unsigned int nbytes = req->cryptlen;

                scatterwalk_start(&src_walk, src);
                scatterwalk_start(&dst_walk, dst);

                while (nbytes) {
                        /* get the source block */
                        scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
                                               false);

                        /* perform KW operation: encrypt block */
                        crypto_cipher_encrypt_one(cipher, (u8 *)&block,
                                                  (u8 *)&block);
                        /* perform KW operation: modify IV with counter */
                        block.A ^= cpu_to_be64(t);
                        t++;

                        /* Copy block->R into place */
                        scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
                                               true);

                        nbytes -= SEMIBSIZE;
                }

                /* we now start to operate on the dst SGL only */
                src = req->dst;
                dst = req->dst;
        }

        /* establish the IV for the caller to pick up */
        memcpy(req->iv, &block.A, SEMIBSIZE);

        memzero_explicit(&block, sizeof(struct crypto_kw_block));

        return 0;
}

static int crypto_kw_create(struct crypto_template *tmpl, struct rtattr **tb)
{
        struct skcipher_instance *inst;
        struct crypto_alg *alg;
        int err;

        inst = skcipher_alloc_instance_simple(tmpl, tb);
        if (IS_ERR(inst))
                return PTR_ERR(inst);

        alg = skcipher_ialg_simple(inst);

        err = -EINVAL;
        /* Section 5.1 requirement for KW */
        if (alg->cra_blocksize != sizeof(struct crypto_kw_block))
                goto out_free_inst;

        inst->alg.base.cra_blocksize = SEMIBSIZE;
        inst->alg.base.cra_alignmask = 0;
        inst->alg.ivsize = SEMIBSIZE;

        inst->alg.encrypt = crypto_kw_encrypt;
        inst->alg.decrypt = crypto_kw_decrypt;

        err = skcipher_register_instance(tmpl, inst);
        if (err) {
out_free_inst:
                inst->free(inst);
        }

        return err;
}

static struct crypto_template crypto_kw_tmpl = {
        .name = "kw",
        .create = crypto_kw_create,
        .module = THIS_MODULE,
};

static int __init crypto_kw_init(void)
{
        return crypto_register_template(&crypto_kw_tmpl);
}

static void __exit crypto_kw_exit(void)
{
        crypto_unregister_template(&crypto_kw_tmpl);
}

subsys_initcall(crypto_kw_init);
module_exit(crypto_kw_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");
MODULE_ALIAS_CRYPTO("kw");
MODULE_IMPORT_NS(CRYPTO_INTERNAL);