crypto: keywrap - add key wrapping block chaining mode

This patch implements the AES key wrapping as specified in
NIST SP800-38F and RFC3394.

The implementation covers key wrapping without padding.

IV handling: The caller does not provide an IV for encryption,
but must obtain the IV after encryption which would serve as the first
semblock in the ciphertext structure defined by SP800-38F. Conversely,
for decryption, the caller must provide the first semiblock of the data
as the IV and the following blocks as ciphertext.

The key wrapping is an authenticated decryption operation. The caller
will receive EBADMSG during decryption if the authentication failed.

Albeit the standards define the key wrapping for AES only, the template
can be used with any other block cipher that has a block size of 16
bytes. During initialization of the template, that condition is checked.
Any cipher not having a block size of 16 bytes will cause the
initialization to fail.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/keywrap.c

@@ -0,0 +1,419 @@
+/*
+ * 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, ptdata, 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, ctdata, ctlen);
+ *	skcipher_request_set_crypt(req, &sg, &sg, ptlen, 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/skcipher.h>
+
+struct crypto_kw_ctx {
+	struct crypto_cipher *child;
+};
+
+struct crypto_kw_block {
+#define SEMIBSIZE 8
+	u8 A[SEMIBSIZE];
+	u8 R[SEMIBSIZE];
+};
+
+/* convert 64 bit integer into its string representation */
+static inline void crypto_kw_cpu_to_be64(u64 val, u8 *buf)
+{
+	__be64 *a = (__be64 *)buf;
+
+	*a = cpu_to_be64(val);
+}
+
+/*
+ * 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;
+		} else
+			skip -= sg->length;
+
+		sg = sg_next(sg);
+	}
+}
+
+static int crypto_kw_decrypt(struct blkcipher_desc *desc,
+			     struct scatterlist *dst, struct scatterlist *src,
+			     unsigned int nbytes)
+{
+	struct crypto_blkcipher *tfm = desc->tfm;
+	struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
+	struct crypto_cipher *child = ctx->child;
+
+	unsigned long alignmask = max_t(unsigned long, SEMIBSIZE,
+					crypto_cipher_alignmask(child));
+	unsigned int i;
+
+	u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask];
+	struct crypto_kw_block *block = (struct crypto_kw_block *)
+					PTR_ALIGN(blockbuf + 0, alignmask + 1);
+
+	u64 t = 6 * ((nbytes) >> 3);
+	struct scatterlist *lsrc, *ldst;
+	int ret = 0;
+
+	/*
+	 * Require at least 2 semiblocks (note, the 3rd semiblock that is
+	 * required by SP800-38F is the IV.
+	 */
+	if (nbytes < (2 * SEMIBSIZE) || nbytes % SEMIBSIZE)
+		return -EINVAL;
+
+	/* Place the IV into block A */
+	memcpy(block->A, desc->info, SEMIBSIZE);
+
+	/*
+	 * src scatterlist is read-only. dst scatterlist is r/w. During the
+	 * first loop, lsrc points to src and ldst to dst. For any
+	 * subsequent round, the code operates on dst only.
+	 */
+	lsrc = src;
+	ldst = dst;
+
+	for (i = 0; i < 6; i++) {
+		u8 tbe_buffer[SEMIBSIZE + alignmask];
+		/* alignment for the crypto_xor and the _to_be64 operation */
+		u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1);
+		unsigned int tmp_nbytes = nbytes;
+		struct scatter_walk src_walk, dst_walk;
+
+		while (tmp_nbytes) {
+			/* move pointer by tmp_nbytes in the SGL */
+			crypto_kw_scatterlist_ff(&src_walk, lsrc, tmp_nbytes);
+			/* get the source block */
+			scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE,
+					       false);
+
+			/* perform KW operation: get counter as byte string */
+			crypto_kw_cpu_to_be64(t, tbe);
+			/* perform KW operation: modify IV with counter */
+			crypto_xor(block->A, tbe, SEMIBSIZE);
+			t--;
+			/* perform KW operation: decrypt block */
+			crypto_cipher_decrypt_one(child, (u8*)block,
+						  (u8*)block);
+
+			/* move pointer by tmp_nbytes in the SGL */
+			crypto_kw_scatterlist_ff(&dst_walk, ldst, tmp_nbytes);
+			/* Copy block->R into place */
+			scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE,
+					       true);
+
+			tmp_nbytes -= SEMIBSIZE;
+		}
+
+		/* we now start to operate on the dst SGL only */
+		lsrc = dst;
+		ldst = dst;
+	}
+
+	/* Perform authentication check */
+	if (crypto_memneq("\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", block->A,
+			  SEMIBSIZE))
+		ret = -EBADMSG;
+
+	memzero_explicit(&block, sizeof(struct crypto_kw_block));
+
+	return ret;
+}
+
+static int crypto_kw_encrypt(struct blkcipher_desc *desc,
+			     struct scatterlist *dst, struct scatterlist *src,
+			     unsigned int nbytes)
+{
+	struct crypto_blkcipher *tfm = desc->tfm;
+	struct crypto_kw_ctx *ctx = crypto_blkcipher_ctx(tfm);
+	struct crypto_cipher *child = ctx->child;
+
+	unsigned long alignmask = max_t(unsigned long, SEMIBSIZE,
+					crypto_cipher_alignmask(child));
+	unsigned int i;
+
+	u8 blockbuf[sizeof(struct crypto_kw_block) + alignmask];
+	struct crypto_kw_block *block = (struct crypto_kw_block *)
+					PTR_ALIGN(blockbuf + 0, alignmask + 1);
+
+	u64 t = 1;
+	struct scatterlist *lsrc, *ldst;
+
+	/*
+	 * 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 (nbytes < (2 * SEMIBSIZE) || nbytes % 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.
+	 */
+	memcpy(block->A, "\xA6\xA6\xA6\xA6\xA6\xA6\xA6\xA6", SEMIBSIZE);
+
+	/*
+	 * src scatterlist is read-only. dst scatterlist is r/w. During the
+	 * first loop, lsrc points to src and ldst to dst. For any
+	 * subsequent round, the code operates on dst only.
+	 */
+	lsrc = src;
+	ldst = dst;
+
+	for (i = 0; i < 6; i++) {
+		u8 tbe_buffer[SEMIBSIZE + alignmask];
+		u8 *tbe = PTR_ALIGN(tbe_buffer + 0, alignmask + 1);
+		unsigned int tmp_nbytes = nbytes;
+		struct scatter_walk src_walk, dst_walk;
+
+		scatterwalk_start(&src_walk, lsrc);
+		scatterwalk_start(&dst_walk, ldst);
+
+		while (tmp_nbytes) {
+			/* get the source block */
+			scatterwalk_copychunks(block->R, &src_walk, SEMIBSIZE,
+					       false);
+
+			/* perform KW operation: encrypt block */
+			crypto_cipher_encrypt_one(child, (u8 *)block,
+						  (u8 *)block);
+			/* perform KW operation: get counter as byte string */
+			crypto_kw_cpu_to_be64(t, tbe);
+			/* perform KW operation: modify IV with counter */
+			crypto_xor(block->A, tbe, SEMIBSIZE);
+			t++;
+
+			/* Copy block->R into place */
+			scatterwalk_copychunks(block->R, &dst_walk, SEMIBSIZE,
+					       true);
+
+			tmp_nbytes -= SEMIBSIZE;
+		}
+
+		/* we now start to operate on the dst SGL only */
+		lsrc = dst;
+		ldst = dst;
+	}
+
+	/* establish the IV for the caller to pick up */
+	memcpy(desc->info, block->A, SEMIBSIZE);
+
+	memzero_explicit(&block, sizeof(struct crypto_kw_block));
+
+	return 0;
+}
+
+static int crypto_kw_setkey(struct crypto_tfm *parent, const u8 *key,
+			    unsigned int keylen)
+{
+	struct crypto_kw_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_kw_init_tfm(struct crypto_tfm *tfm)
+{
+	struct crypto_instance *inst = crypto_tfm_alg_instance(tfm);
+	struct crypto_spawn *spawn = crypto_instance_ctx(inst);
+	struct crypto_kw_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_kw_exit_tfm(struct crypto_tfm *tfm)
+{
+	struct crypto_kw_ctx *ctx = crypto_tfm_ctx(tfm);
+
+	crypto_free_cipher(ctx->child);
+}
+
+static struct crypto_instance *crypto_kw_alloc(struct rtattr **tb)
+{
+	struct crypto_instance *inst = NULL;
+	struct crypto_alg *alg = NULL;
+	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);
+	/* Section 5.1 requirement for KW */
+	if (alg->cra_blocksize != sizeof(struct crypto_kw_block))
+		goto err;
+
+	inst = crypto_alloc_instance("kw", alg);
+	if (IS_ERR(inst))
+		goto err;
+
+	inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
+	inst->alg.cra_priority = alg->cra_priority;
+	inst->alg.cra_blocksize = SEMIBSIZE;
+	inst->alg.cra_alignmask = 0;
+	inst->alg.cra_type = &crypto_blkcipher_type;
+	inst->alg.cra_blkcipher.ivsize = SEMIBSIZE;
+	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_kw_ctx);
+
+	inst->alg.cra_init = crypto_kw_init_tfm;
+	inst->alg.cra_exit = crypto_kw_exit_tfm;
+
+	inst->alg.cra_blkcipher.setkey = crypto_kw_setkey;
+	inst->alg.cra_blkcipher.encrypt = crypto_kw_encrypt;
+	inst->alg.cra_blkcipher.decrypt = crypto_kw_decrypt;
+
+err:
+	crypto_mod_put(alg);
+	return inst;
+}
+
+static void crypto_kw_free(struct crypto_instance *inst)
+{
+	crypto_drop_spawn(crypto_instance_ctx(inst));
+	kfree(inst);
+}
+
+static struct crypto_template crypto_kw_tmpl = {
+	.name = "kw",
+	.alloc = crypto_kw_alloc,
+	.free = crypto_kw_free,
+	.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);
+}
+
+module_init(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");