/* * 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");