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+/*
+ * 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);