--- /dev/null
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * XCTR: XOR Counter mode - Adapted from ctr.c
+ *
+ * (C) Copyright IBM Corp. 2007 - Joy Latten <latten@us.ibm.com>
+ * Copyright 2021 Google LLC
+ */
+
+/*
+ * XCTR mode is a blockcipher mode of operation used to implement HCTR2. XCTR is
+ * closely related to the CTR mode of operation; the main difference is that CTR
+ * generates the keystream using E(CTR + IV) whereas XCTR generates the
+ * keystream using E(CTR ^ IV). This allows implementations to avoid dealing
+ * with multi-limb integers (as is required in CTR mode). XCTR is also specified
+ * using little-endian arithmetic which makes it slightly faster on LE machines.
+ *
+ * See the HCTR2 paper for more details:
+ * Length-preserving encryption with HCTR2
+ * (https://eprint.iacr.org/2021/1441.pdf)
+ */
+
+#include <crypto/algapi.h>
+#include <crypto/internal/cipher.h>
+#include <crypto/internal/skcipher.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+
+/* For now this implementation is limited to 16-byte blocks for simplicity */
+#define XCTR_BLOCKSIZE 16
+
+static void crypto_xctr_crypt_final(struct skcipher_walk *walk,
+ struct crypto_cipher *tfm, u32 byte_ctr)
+{
+ u8 keystream[XCTR_BLOCKSIZE];
+ const u8 *src = walk->src.virt.addr;
+ u8 *dst = walk->dst.virt.addr;
+ unsigned int nbytes = walk->nbytes;
+ __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);
+
+ crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
+ crypto_cipher_encrypt_one(tfm, keystream, walk->iv);
+ crypto_xor_cpy(dst, keystream, src, nbytes);
+ crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
+}
+
+static int crypto_xctr_crypt_segment(struct skcipher_walk *walk,
+ struct crypto_cipher *tfm, u32 byte_ctr)
+{
+ void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
+ crypto_cipher_alg(tfm)->cia_encrypt;
+ const u8 *src = walk->src.virt.addr;
+ u8 *dst = walk->dst.virt.addr;
+ unsigned int nbytes = walk->nbytes;
+ __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);
+
+ do {
+ crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
+ fn(crypto_cipher_tfm(tfm), dst, walk->iv);
+ crypto_xor(dst, src, XCTR_BLOCKSIZE);
+ crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
+
+ le32_add_cpu(&ctr32, 1);
+
+ src += XCTR_BLOCKSIZE;
+ dst += XCTR_BLOCKSIZE;
+ } while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE);
+
+ return nbytes;
+}
+
+static int crypto_xctr_crypt_inplace(struct skcipher_walk *walk,
+ struct crypto_cipher *tfm, u32 byte_ctr)
+{
+ void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
+ crypto_cipher_alg(tfm)->cia_encrypt;
+ unsigned long alignmask = crypto_cipher_alignmask(tfm);
+ unsigned int nbytes = walk->nbytes;
+ u8 *data = walk->src.virt.addr;
+ u8 tmp[XCTR_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
+ u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1);
+ __le32 ctr32 = cpu_to_le32(byte_ctr / XCTR_BLOCKSIZE + 1);
+
+ do {
+ crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
+ fn(crypto_cipher_tfm(tfm), keystream, walk->iv);
+ crypto_xor(data, keystream, XCTR_BLOCKSIZE);
+ crypto_xor(walk->iv, (u8 *)&ctr32, sizeof(ctr32));
+
+ le32_add_cpu(&ctr32, 1);
+
+ data += XCTR_BLOCKSIZE;
+ } while ((nbytes -= XCTR_BLOCKSIZE) >= XCTR_BLOCKSIZE);
+
+ return nbytes;
+}
+
+static int crypto_xctr_crypt(struct skcipher_request *req)
+{
+ struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+ struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
+ struct skcipher_walk walk;
+ unsigned int nbytes;
+ int err;
+ u32 byte_ctr = 0;
+
+ err = skcipher_walk_virt(&walk, req, false);
+
+ while (walk.nbytes >= XCTR_BLOCKSIZE) {
+ if (walk.src.virt.addr == walk.dst.virt.addr)
+ nbytes = crypto_xctr_crypt_inplace(&walk, cipher,
+ byte_ctr);
+ else
+ nbytes = crypto_xctr_crypt_segment(&walk, cipher,
+ byte_ctr);
+
+ byte_ctr += walk.nbytes - nbytes;
+ err = skcipher_walk_done(&walk, nbytes);
+ }
+
+ if (walk.nbytes) {
+ crypto_xctr_crypt_final(&walk, cipher, byte_ctr);
+ err = skcipher_walk_done(&walk, 0);
+ }
+
+ return err;
+}
+
+static int crypto_xctr_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);
+
+ /* Block size must be 16 bytes. */
+ err = -EINVAL;
+ if (alg->cra_blocksize != XCTR_BLOCKSIZE)
+ goto out_free_inst;
+
+ /* XCTR mode is a stream cipher. */
+ inst->alg.base.cra_blocksize = 1;
+
+ /*
+ * To simplify the implementation, configure the skcipher walk to only
+ * give a partial block at the very end, never earlier.
+ */
+ inst->alg.chunksize = alg->cra_blocksize;
+
+ inst->alg.encrypt = crypto_xctr_crypt;
+ inst->alg.decrypt = crypto_xctr_crypt;
+
+ err = skcipher_register_instance(tmpl, inst);
+ if (err) {
+out_free_inst:
+ inst->free(inst);
+ }
+
+ return err;
+}
+
+static struct crypto_template crypto_xctr_tmpl = {
+ .name = "xctr",
+ .create = crypto_xctr_create,
+ .module = THIS_MODULE,
+};
+
+static int __init crypto_xctr_module_init(void)
+{
+ return crypto_register_template(&crypto_xctr_tmpl);
+}
+
+static void __exit crypto_xctr_module_exit(void)
+{
+ crypto_unregister_template(&crypto_xctr_tmpl);
+}
+
+subsys_initcall(crypto_xctr_module_init);
+module_exit(crypto_xctr_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("XCTR block cipher mode of operation");
+MODULE_ALIAS_CRYPTO("xctr");
+MODULE_IMPORT_NS(CRYPTO_INTERNAL);
projects / linux-2.6-microblaze.git / blobdiff