321 lines
9.5 KiB
C
321 lines
9.5 KiB
C
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/*
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* Key Wrapping: RFC3394 / NIST SP800-38F
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*
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* Copyright (C) 2015, Stephan Mueller <smueller@chronox.de>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, and the entire permission notice in its entirety,
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* including the disclaimer of warranties.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote
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* products derived from this software without specific prior
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* written permission.
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*
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* ALTERNATIVELY, this product may be distributed under the terms of
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* the GNU General Public License, in which case the provisions of the GPL2
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* are required INSTEAD OF the above restrictions. (This clause is
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* necessary due to a potential bad interaction between the GPL and
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* the restrictions contained in a BSD-style copyright.)
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
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* WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
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* OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
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* USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*/
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/*
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* Note for using key wrapping:
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*
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* * The result of the encryption operation is the ciphertext starting
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* with the 2nd semiblock. The first semiblock is provided as the IV.
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* The IV used to start the encryption operation is the default IV.
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*
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* * The input for the decryption is the first semiblock handed in as an
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* IV. The ciphertext is the data starting with the 2nd semiblock. The
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* return code of the decryption operation will be EBADMSG in case an
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* integrity error occurs.
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*
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* To obtain the full result of an encryption as expected by SP800-38F, the
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* caller must allocate a buffer of plaintext + 8 bytes:
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*
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* unsigned int datalen = ptlen + crypto_skcipher_ivsize(tfm);
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* u8 data[datalen];
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* u8 *iv = data;
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* u8 *pt = data + crypto_skcipher_ivsize(tfm);
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* <ensure that pt contains the plaintext of size ptlen>
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* sg_init_one(&sg, pt, ptlen);
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* skcipher_request_set_crypt(req, &sg, &sg, ptlen, iv);
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*
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* ==> After encryption, data now contains full KW result as per SP800-38F.
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*
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* In case of decryption, ciphertext now already has the expected length
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* and must be segmented appropriately:
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*
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* unsigned int datalen = CTLEN;
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* u8 data[datalen];
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* <ensure that data contains full ciphertext>
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* u8 *iv = data;
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* u8 *ct = data + crypto_skcipher_ivsize(tfm);
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* unsigned int ctlen = datalen - crypto_skcipher_ivsize(tfm);
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* sg_init_one(&sg, ct, ctlen);
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* skcipher_request_set_crypt(req, &sg, &sg, ctlen, iv);
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*
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* ==> After decryption (which hopefully does not return EBADMSG), the ct
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* pointer now points to the plaintext of size ctlen.
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*
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* Note 2: KWP is not implemented as this would defy in-place operation.
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* If somebody wants to wrap non-aligned data, he should simply pad
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* the input with zeros to fill it up to the 8 byte boundary.
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*/
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#include <linux/module.h>
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#include <linux/crypto.h>
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#include <linux/scatterlist.h>
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#include <crypto/scatterwalk.h>
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#include <crypto/internal/cipher.h>
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#include <crypto/internal/skcipher.h>
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struct crypto_kw_block {
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#define SEMIBSIZE 8
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__be64 A;
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__be64 R;
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};
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/*
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* Fast forward the SGL to the "end" length minus SEMIBSIZE.
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* The start in the SGL defined by the fast-forward is returned with
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* the walk variable
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*/
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static void crypto_kw_scatterlist_ff(struct scatter_walk *walk,
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struct scatterlist *sg,
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unsigned int end)
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{
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unsigned int skip = 0;
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/* The caller should only operate on full SEMIBLOCKs. */
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BUG_ON(end < SEMIBSIZE);
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skip = end - SEMIBSIZE;
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while (sg) {
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if (sg->length > skip) {
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scatterwalk_start(walk, sg);
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scatterwalk_advance(walk, skip);
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break;
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}
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skip -= sg->length;
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sg = sg_next(sg);
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}
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}
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static int crypto_kw_decrypt(struct skcipher_request *req)
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{
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struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
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struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
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struct crypto_kw_block block;
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struct scatterlist *src, *dst;
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u64 t = 6 * ((req->cryptlen) >> 3);
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unsigned int i;
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int ret = 0;
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/*
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* Require at least 2 semiblocks (note, the 3rd semiblock that is
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* required by SP800-38F is the IV.
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*/
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if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
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return -EINVAL;
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/* Place the IV into block A */
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memcpy(&block.A, req->iv, SEMIBSIZE);
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/*
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* src scatterlist is read-only. dst scatterlist is r/w. During the
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* first loop, src points to req->src and dst to req->dst. For any
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* subsequent round, the code operates on req->dst only.
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*/
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src = req->src;
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dst = req->dst;
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for (i = 0; i < 6; i++) {
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struct scatter_walk src_walk, dst_walk;
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unsigned int nbytes = req->cryptlen;
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while (nbytes) {
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/* move pointer by nbytes in the SGL */
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crypto_kw_scatterlist_ff(&src_walk, src, nbytes);
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/* get the source block */
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scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
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false);
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/* perform KW operation: modify IV with counter */
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block.A ^= cpu_to_be64(t);
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t--;
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/* perform KW operation: decrypt block */
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crypto_cipher_decrypt_one(cipher, (u8 *)&block,
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(u8 *)&block);
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/* move pointer by nbytes in the SGL */
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crypto_kw_scatterlist_ff(&dst_walk, dst, nbytes);
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/* Copy block->R into place */
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scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
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true);
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nbytes -= SEMIBSIZE;
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}
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/* we now start to operate on the dst SGL only */
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src = req->dst;
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dst = req->dst;
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}
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/* Perform authentication check */
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if (block.A != cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL))
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ret = -EBADMSG;
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memzero_explicit(&block, sizeof(struct crypto_kw_block));
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return ret;
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}
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static int crypto_kw_encrypt(struct skcipher_request *req)
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{
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struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
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struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
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struct crypto_kw_block block;
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struct scatterlist *src, *dst;
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u64 t = 1;
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unsigned int i;
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/*
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* Require at least 2 semiblocks (note, the 3rd semiblock that is
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* required by SP800-38F is the IV that occupies the first semiblock.
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* This means that the dst memory must be one semiblock larger than src.
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* Also ensure that the given data is aligned to semiblock.
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*/
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if (req->cryptlen < (2 * SEMIBSIZE) || req->cryptlen % SEMIBSIZE)
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return -EINVAL;
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/*
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* Place the predefined IV into block A -- for encrypt, the caller
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* does not need to provide an IV, but he needs to fetch the final IV.
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*/
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block.A = cpu_to_be64(0xa6a6a6a6a6a6a6a6ULL);
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/*
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* src scatterlist is read-only. dst scatterlist is r/w. During the
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* first loop, src points to req->src and dst to req->dst. For any
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* subsequent round, the code operates on req->dst only.
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*/
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src = req->src;
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dst = req->dst;
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for (i = 0; i < 6; i++) {
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struct scatter_walk src_walk, dst_walk;
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unsigned int nbytes = req->cryptlen;
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scatterwalk_start(&src_walk, src);
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scatterwalk_start(&dst_walk, dst);
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while (nbytes) {
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/* get the source block */
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scatterwalk_copychunks(&block.R, &src_walk, SEMIBSIZE,
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false);
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/* perform KW operation: encrypt block */
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crypto_cipher_encrypt_one(cipher, (u8 *)&block,
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(u8 *)&block);
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/* perform KW operation: modify IV with counter */
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block.A ^= cpu_to_be64(t);
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t++;
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/* Copy block->R into place */
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scatterwalk_copychunks(&block.R, &dst_walk, SEMIBSIZE,
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true);
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nbytes -= SEMIBSIZE;
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}
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/* we now start to operate on the dst SGL only */
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src = req->dst;
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dst = req->dst;
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}
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/* establish the IV for the caller to pick up */
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memcpy(req->iv, &block.A, SEMIBSIZE);
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memzero_explicit(&block, sizeof(struct crypto_kw_block));
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return 0;
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}
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static int crypto_kw_create(struct crypto_template *tmpl, struct rtattr **tb)
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{
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struct skcipher_instance *inst;
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struct crypto_alg *alg;
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int err;
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inst = skcipher_alloc_instance_simple(tmpl, tb);
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if (IS_ERR(inst))
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return PTR_ERR(inst);
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alg = skcipher_ialg_simple(inst);
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err = -EINVAL;
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/* Section 5.1 requirement for KW */
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if (alg->cra_blocksize != sizeof(struct crypto_kw_block))
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goto out_free_inst;
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inst->alg.base.cra_blocksize = SEMIBSIZE;
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inst->alg.base.cra_alignmask = 0;
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inst->alg.ivsize = SEMIBSIZE;
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inst->alg.encrypt = crypto_kw_encrypt;
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inst->alg.decrypt = crypto_kw_decrypt;
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err = skcipher_register_instance(tmpl, inst);
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if (err) {
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out_free_inst:
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inst->free(inst);
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}
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return err;
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}
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static struct crypto_template crypto_kw_tmpl = {
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.name = "kw",
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.create = crypto_kw_create,
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.module = THIS_MODULE,
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};
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static int __init crypto_kw_init(void)
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{
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return crypto_register_template(&crypto_kw_tmpl);
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}
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static void __exit crypto_kw_exit(void)
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{
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crypto_unregister_template(&crypto_kw_tmpl);
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}
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subsys_initcall(crypto_kw_init);
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module_exit(crypto_kw_exit);
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MODULE_LICENSE("Dual BSD/GPL");
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MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
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MODULE_DESCRIPTION("Key Wrapping (RFC3394 / NIST SP800-38F)");
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MODULE_ALIAS_CRYPTO("kw");
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MODULE_IMPORT_NS(CRYPTO_INTERNAL);
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