1 files changed, 104 insertions, 0 deletions
diff --git a/crypto/ofb.c b/crypto/ofb.c
new file mode 100644
index 000000000..2ec68e3f2
--- /dev/null
+++ b/crypto/ofb.c
@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * OFB: Output FeedBack mode
+ *
+ * Copyright (C) 2018 ARM Limited or its affiliates.
+ * All rights reserved.
+ */
+
+#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>
+
+static int crypto_ofb_crypt(struct skcipher_request *req)
+{
+	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+	struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
+	const unsigned int bsize = crypto_cipher_blocksize(cipher);
+	struct skcipher_walk walk;
+	int err;
+
+	err = skcipher_walk_virt(&walk, req, false);
+
+	while (walk.nbytes >= bsize) {
+		const u8 *src = walk.src.virt.addr;
+		u8 *dst = walk.dst.virt.addr;
+		u8 * const iv = walk.iv;
+		unsigned int nbytes = walk.nbytes;
+
+		do {
+			crypto_cipher_encrypt_one(cipher, iv, iv);
+			crypto_xor_cpy(dst, src, iv, bsize);
+			dst += bsize;
+			src += bsize;
+		} while ((nbytes -= bsize) >= bsize);
+
+		err = skcipher_walk_done(&walk, nbytes);
+	}
+
+	if (walk.nbytes) {
+		crypto_cipher_encrypt_one(cipher, walk.iv, walk.iv);
+		crypto_xor_cpy(walk.dst.virt.addr, walk.src.virt.addr, walk.iv,
+			       walk.nbytes);
+		err = skcipher_walk_done(&walk, 0);
+	}
+	return err;
+}
+
+static int crypto_ofb_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);
+
+	/* OFB 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_ofb_crypt;
+	inst->alg.decrypt = crypto_ofb_crypt;
+
+	err = skcipher_register_instance(tmpl, inst);
+	if (err)
+		inst->free(inst);
+
+	return err;
+}
+
+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);
+}
+
+subsys_initcall(crypto_ofb_module_init);
+module_exit(crypto_ofb_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("OFB block cipher mode of operation");
+MODULE_ALIAS_CRYPTO("ofb");