crypto: ofb - add output feedback mode

Add a generic version of output feedback mode. We already have support of
several hardware based transformations of this mode and the needed test
vectors but we somehow missed adding a generic software one. Fix this now.

Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

3 files changed, 238 insertions, 0 deletions

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 4ef95b0b25a3..63ef279322d2 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -456,6 +456,18 @@ config CRYPTO_LRW
           The first 128, 192 or 256 bits in the key are used for AES and the
           rest is used to tie each cipher block to its logical position.
 
+config CRYPTO_OFB
+        tristate "OFB support"
+        select CRYPTO_BLKCIPHER
+        select CRYPTO_MANAGER
+        help
+          OFB: the Output Feedback mode makes a block cipher into a synchronous
+          stream cipher. It generates keystream blocks, which are then XORed
+          with the plaintext blocks to get the ciphertext. Flipping a bit in the
+          ciphertext produces a flipped bit in the plaintext at the same
+          location. This property allows many error correcting codes to function
+          normally even when applied before encryption.
+
 config CRYPTO_PCBC
         tristate "PCBC support"
         select CRYPTO_BLKCIPHER
diff --git a/crypto/Makefile b/crypto/Makefile
index ff5c2bbda04a..5c207c76abf7 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -142,6 +142,7 @@ obj-$(CONFIG_CRYPTO_USER_API_SKCIPHER) += algif_skcipher.o
 obj-$(CONFIG_CRYPTO_USER_API_RNG) += algif_rng.o
 obj-$(CONFIG_CRYPTO_USER_API_AEAD) += algif_aead.o
 obj-$(CONFIG_CRYPTO_ZSTD) += zstd.o
+obj-$(CONFIG_CRYPTO_OFB) += ofb.o
 
 ecdh_generic-y := ecc.o
 ecdh_generic-y += ecdh.o
diff --git a/crypto/ofb.c b/crypto/ofb.c
new file mode 100644
index 000000000000..886631708c5e
--- /dev/null
+++ b/crypto/ofb.c
@@ -0,0 +1,225 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * OFB: Output FeedBack mode
+ *
+ * Copyright (C) 2018 ARM Limited or its affiliates.
+ * All rights reserved.
+ *
+ * Based loosely on public domain code gleaned from libtomcrypt
+ * (https://github.com/libtom/libtomcrypt).
+ */
+
+#include <crypto/algapi.h>
+#include <crypto/internal/skcipher.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/scatterlist.h>
+#include <linux/slab.h>
+
+struct crypto_ofb_ctx {
+        struct crypto_cipher *child;
+        int cnt;
+};
+
+
+static int crypto_ofb_setkey(struct crypto_skcipher *parent, const u8 *key,
+                             unsigned int keylen)
+{
+        struct crypto_ofb_ctx *ctx = crypto_skcipher_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_skcipher_get_flags(parent) &
+                                       CRYPTO_TFM_REQ_MASK);
+        err = crypto_cipher_setkey(child, key, keylen);
+        crypto_skcipher_set_flags(parent, crypto_cipher_get_flags(child) &
+                                  CRYPTO_TFM_RES_MASK);
+        return err;
+}
+
+static int crypto_ofb_encrypt_segment(struct crypto_ofb_ctx *ctx,
+                                      struct skcipher_walk *walk,
+                                      struct crypto_cipher *tfm)
+{
+        int bsize = crypto_cipher_blocksize(tfm);
+        int nbytes = walk->nbytes;
+
+        u8 *src = walk->src.virt.addr;
+        u8 *dst = walk->dst.virt.addr;
+        u8 *iv = walk->iv;
+
+        do {
+                if (ctx->cnt == bsize) {
+                        if (nbytes < bsize)
+                                break;
+                        crypto_cipher_encrypt_one(tfm, iv, iv);
+                        ctx->cnt = 0;
+                }
+                *dst = *src ^ iv[ctx->cnt];
+                src++;
+                dst++;
+                ctx->cnt++;
+        } while (--nbytes);
+        return nbytes;
+}
+
+static int crypto_ofb_encrypt(struct skcipher_request *req)
+{
+        struct skcipher_walk walk;
+        struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+        unsigned int bsize;
+        struct crypto_ofb_ctx *ctx = crypto_skcipher_ctx(tfm);
+        struct crypto_cipher *child = ctx->child;
+        int ret = 0;
+
+        bsize =  crypto_cipher_blocksize(child);
+        ctx->cnt = bsize;
+
+        ret = skcipher_walk_virt(&walk, req, false);
+
+        while (walk.nbytes) {
+                ret = crypto_ofb_encrypt_segment(ctx, &walk, child);
+                ret = skcipher_walk_done(&walk, ret);
+        }
+
+        return ret;
+}
+
+/* OFB encrypt and decrypt are identical */
+static int crypto_ofb_decrypt(struct skcipher_request *req)
+{
+        return crypto_ofb_encrypt(req);
+}
+
+static int crypto_ofb_init_tfm(struct crypto_skcipher *tfm)
+{
+        struct skcipher_instance *inst = skcipher_alg_instance(tfm);
+        struct crypto_spawn *spawn = skcipher_instance_ctx(inst);
+        struct crypto_ofb_ctx *ctx = crypto_skcipher_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_ofb_exit_tfm(struct crypto_skcipher *tfm)
+{
+        struct crypto_ofb_ctx *ctx = crypto_skcipher_ctx(tfm);
+
+        crypto_free_cipher(ctx->child);
+}
+
+static void crypto_ofb_free(struct skcipher_instance *inst)
+{
+        crypto_drop_skcipher(skcipher_instance_ctx(inst));
+        kfree(inst);
+}
+
+static int crypto_ofb_create(struct crypto_template *tmpl, struct rtattr **tb)
+{
+        struct skcipher_instance *inst;
+        struct crypto_attr_type *algt;
+        struct crypto_spawn *spawn;
+        struct crypto_alg *alg;
+        u32 mask;
+        int err;
+
+        err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER);
+        if (err)
+                return err;
+
+        inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
+        if (!inst)
+                return -ENOMEM;
+
+        algt = crypto_get_attr_type(tb);
+        err = PTR_ERR(algt);
+        if (IS_ERR(algt))
+                goto err_free_inst;
+
+        mask = CRYPTO_ALG_TYPE_MASK |
+                crypto_requires_off(algt->type, algt->mask,
+                                    CRYPTO_ALG_NEED_FALLBACK);
+
+        alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER, mask);
+        err = PTR_ERR(alg);
+        if (IS_ERR(alg))
+                goto err_free_inst;
+
+        spawn = skcipher_instance_ctx(inst);
+        err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst),
+                                CRYPTO_ALG_TYPE_MASK);
+        crypto_mod_put(alg);
+        if (err)
+                goto err_free_inst;
+
+        err = crypto_inst_setname(skcipher_crypto_instance(inst), "ofb", alg);
+        if (err)
+                goto err_drop_spawn;
+
+        inst->alg.base.cra_priority = alg->cra_priority;
+        inst->alg.base.cra_blocksize = alg->cra_blocksize;
+        inst->alg.base.cra_alignmask = alg->cra_alignmask;
+
+        /* We access the data as u32s when xoring. */
+        inst->alg.base.cra_alignmask |= __alignof__(u32) - 1;
+
+        inst->alg.ivsize = alg->cra_blocksize;
+        inst->alg.min_keysize = alg->cra_cipher.cia_min_keysize;
+        inst->alg.max_keysize = alg->cra_cipher.cia_max_keysize;
+
+        inst->alg.base.cra_ctxsize = sizeof(struct crypto_ofb_ctx);
+
+        inst->alg.init = crypto_ofb_init_tfm;
+        inst->alg.exit = crypto_ofb_exit_tfm;
+
+        inst->alg.setkey = crypto_ofb_setkey;
+        inst->alg.encrypt = crypto_ofb_encrypt;
+        inst->alg.decrypt = crypto_ofb_decrypt;
+
+        inst->free = crypto_ofb_free;
+
+        err = skcipher_register_instance(tmpl, inst);
+        if (err)
+                goto err_drop_spawn;
+
+out:
+        return err;
+
+err_drop_spawn:
+        crypto_drop_spawn(spawn);
+err_free_inst:
+        kfree(inst);
+        goto out;
+}
+
+static struct crypto_template crypto_ofb_tmpl = {
+        .name = "ofb",
+        .create = crypto_ofb_create,
+        .module = THIS_MODULE,
+};
+
+static int __init crypto_ofb_module_init(void)
+{
+        return crypto_register_template(&crypto_ofb_tmpl);
+}
+
+static void __exit crypto_ofb_module_exit(void)
+{
+        crypto_unregister_template(&crypto_ofb_tmpl);
+}
+
+module_init(crypto_ofb_module_init);
+module_exit(crypto_ofb_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("OFB block cipher algorithm");
+MODULE_ALIAS_CRYPTO("ofb");