crypto: dh - Add DH software implementation

* Implement MPI based Diffie-Hellman under kpp API
 * Test provided uses data generad by OpenSSL

Signed-off-by: Salvatore Benedetto <salvatore.benedetto@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 189 insertions, 0 deletions

diff --git a/crypto/dh.c b/crypto/dh.c
new file mode 100644
index 000000000000..5e960fe28681
--- /dev/null
+++ b/crypto/dh.c
@@ -0,0 +1,189 @@
+/*  Diffie-Hellman Key Agreement Method [RFC2631]
+ *
+ * Copyright (c) 2016, Intel Corporation
+ * Authors: Salvatore Benedetto <salvatore.benedetto@intel.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/module.h>
+#include <crypto/internal/kpp.h>
+#include <crypto/kpp.h>
+#include <crypto/dh.h>
+#include <linux/mpi.h>
+
+struct dh_ctx {
+	MPI p;
+	MPI g;
+	MPI xa;
+};
+
+static inline void dh_clear_params(struct dh_ctx *ctx)
+{
+	mpi_free(ctx->p);
+	mpi_free(ctx->g);
+	ctx->p = NULL;
+	ctx->g = NULL;
+}
+
+static void dh_free_ctx(struct dh_ctx *ctx)
+{
+	dh_clear_params(ctx);
+	mpi_free(ctx->xa);
+	ctx->xa = NULL;
+}
+
+/*
+ * If base is g we compute the public key
+ *	ya = g^xa mod p; [RFC2631 sec 2.1.1]
+ * else if base if the counterpart public key we compute the shared secret
+ *	ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
+ */
+static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
+{
+	/* val = base^xa mod p */
+	return mpi_powm(val, base, ctx->xa, ctx->p);
+}
+
+static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
+{
+	return kpp_tfm_ctx(tfm);
+}
+
+static int dh_check_params_length(unsigned int p_len)
+{
+	return (p_len < 1536) ? -EINVAL : 0;
+}
+
+static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
+{
+	if (unlikely(!params->p || !params->g))
+		return -EINVAL;
+
+	if (dh_check_params_length(params->p_size << 3))
+		return -EINVAL;
+
+	ctx->p = mpi_read_raw_data(params->p, params->p_size);
+	if (!ctx->p)
+		return -EINVAL;
+
+	ctx->g = mpi_read_raw_data(params->g, params->g_size);
+	if (!ctx->g) {
+		mpi_free(ctx->p);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int dh_set_secret(struct crypto_kpp *tfm, void *buf, unsigned int len)
+{
+	struct dh_ctx *ctx = dh_get_ctx(tfm);
+	struct dh params;
+
+	if (crypto_dh_decode_key(buf, len, &params) < 0)
+		return -EINVAL;
+
+	if (dh_set_params(ctx, &params) < 0)
+		return -EINVAL;
+
+	ctx->xa = mpi_read_raw_data(params.key, params.key_size);
+	if (!ctx->xa) {
+		dh_clear_params(ctx);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int dh_compute_value(struct kpp_request *req)
+{
+	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
+	struct dh_ctx *ctx = dh_get_ctx(tfm);
+	MPI base, val = mpi_alloc(0);
+	int ret = 0;
+	int sign;
+
+	if (!val)
+		return -ENOMEM;
+
+	if (unlikely(!ctx->xa)) {
+		ret = -EINVAL;
+		goto err_free_val;
+	}
+
+	if (req->src) {
+		base = mpi_read_raw_from_sgl(req->src, req->src_len);
+		if (!base) {
+			ret = EINVAL;
+			goto err_free_val;
+		}
+	} else {
+		base = ctx->g;
+	}
+
+	ret = _compute_val(ctx, base, val);
+	if (ret)
+		goto err_free_base;
+
+	ret = mpi_write_to_sgl(val, req->dst, &req->dst_len, &sign);
+	if (ret)
+		goto err_free_base;
+
+	if (sign < 0)
+		ret = -EBADMSG;
+err_free_base:
+	if (req->src)
+		mpi_free(base);
+err_free_val:
+	mpi_free(val);
+	return ret;
+}
+
+static int dh_max_size(struct crypto_kpp *tfm)
+{
+	struct dh_ctx *ctx = dh_get_ctx(tfm);
+
+	return mpi_get_size(ctx->p);
+}
+
+static void dh_exit_tfm(struct crypto_kpp *tfm)
+{
+	struct dh_ctx *ctx = dh_get_ctx(tfm);
+
+	dh_free_ctx(ctx);
+}
+
+static struct kpp_alg dh = {
+	.set_secret = dh_set_secret,
+	.generate_public_key = dh_compute_value,
+	.compute_shared_secret = dh_compute_value,
+	.max_size = dh_max_size,
+	.exit = dh_exit_tfm,
+	.base = {
+		.cra_name = "dh",
+		.cra_driver_name = "dh-generic",
+		.cra_priority = 100,
+		.cra_module = THIS_MODULE,
+		.cra_ctxsize = sizeof(struct dh_ctx),
+	},
+};
+
+static int dh_init(void)
+{
+	return crypto_register_kpp(&dh);
+}
+
+static void dh_exit(void)
+{
+	crypto_unregister_kpp(&dh);
+}
+
+module_init(dh_init);
+module_exit(dh_exit);
+MODULE_ALIAS_CRYPTO("dh");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("DH generic algorithm");