1/*  Diffie-Hellman Key Agreement Method [RFC2631]
  2 *
  3 * Copyright (c) 2016, Intel Corporation
  4 * Authors: Salvatore Benedetto <salvatore.benedetto@intel.com>
  5 *
  6 * This program is free software; you can redistribute it and/or
  7 * modify it under the terms of the GNU General Public License
  8 * as published by the Free Software Foundation; either version
  9 * 2 of the License, or (at your option) any later version.
 10 */
 11
 12#include <linux/module.h>
 13#include <crypto/internal/kpp.h>
 14#include <crypto/kpp.h>
 15#include <crypto/dh.h>
 16#include <linux/mpi.h>
 17
 18struct dh_ctx {
 19	MPI p;
 20	MPI g;
 21	MPI xa;
 22};
 23
 24static void dh_clear_ctx(struct dh_ctx *ctx)
 25{
 26	mpi_free(ctx->p);
 27	mpi_free(ctx->g);
 28	mpi_free(ctx->xa);
 29	memset(ctx, 0, sizeof(*ctx));
 30}
 31
 32/*
 33 * If base is g we compute the public key
 34 *	ya = g^xa mod p; [RFC2631 sec 2.1.1]
 35 * else if base if the counterpart public key we compute the shared secret
 36 *	ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
 37 */
 38static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
 39{
 40	/* val = base^xa mod p */
 41	return mpi_powm(val, base, ctx->xa, ctx->p);
 42}
 43
 44static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
 45{
 46	return kpp_tfm_ctx(tfm);
 47}
 48
 49static int dh_check_params_length(unsigned int p_len)
 50{
 51	return (p_len < 1536) ? -EINVAL : 0;
 52}
 53
 54static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
 55{
 56	if (dh_check_params_length(params->p_size << 3))
 57		return -EINVAL;
 58
 59	ctx->p = mpi_read_raw_data(params->p, params->p_size);
 60	if (!ctx->p)
 61		return -EINVAL;
 62
 63	ctx->g = mpi_read_raw_data(params->g, params->g_size);
 64	if (!ctx->g)
 65		return -EINVAL;
 66
 67	return 0;
 68}
 69
 70static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
 71			 unsigned int len)
 72{
 73	struct dh_ctx *ctx = dh_get_ctx(tfm);
 74	struct dh params;
 75
 76	/* Free the old MPI key if any */
 77	dh_clear_ctx(ctx);
 78
 79	if (crypto_dh_decode_key(buf, len, &params) < 0)
 80		goto err_clear_ctx;
 81
 82	if (dh_set_params(ctx, &params) < 0)
 83		goto err_clear_ctx;
 84
 85	ctx->xa = mpi_read_raw_data(params.key, params.key_size);
 86	if (!ctx->xa)
 87		goto err_clear_ctx;
 88
 89	return 0;
 90
 91err_clear_ctx:
 92	dh_clear_ctx(ctx);
 93	return -EINVAL;
 94}
 95
 96static int dh_compute_value(struct kpp_request *req)
 97{
 98	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
 99	struct dh_ctx *ctx = dh_get_ctx(tfm);
100	MPI base, val = mpi_alloc(0);
101	int ret = 0;
102	int sign;
103
104	if (!val)
105		return -ENOMEM;
106
107	if (unlikely(!ctx->xa)) {
108		ret = -EINVAL;
109		goto err_free_val;
110	}
111
112	if (req->src) {
113		base = mpi_read_raw_from_sgl(req->src, req->src_len);
114		if (!base) {
115			ret = -EINVAL;
116			goto err_free_val;
117		}
118	} else {
119		base = ctx->g;
120	}
121
122	ret = _compute_val(ctx, base, val);
123	if (ret)
124		goto err_free_base;
125
126	ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
127	if (ret)
128		goto err_free_base;
129
130	if (sign < 0)
131		ret = -EBADMSG;
132err_free_base:
133	if (req->src)
134		mpi_free(base);
135err_free_val:
136	mpi_free(val);
137	return ret;
138}
139
140static unsigned int dh_max_size(struct crypto_kpp *tfm)
141{
142	struct dh_ctx *ctx = dh_get_ctx(tfm);
143
144	return mpi_get_size(ctx->p);
145}
146
147static void dh_exit_tfm(struct crypto_kpp *tfm)
148{
149	struct dh_ctx *ctx = dh_get_ctx(tfm);
150
151	dh_clear_ctx(ctx);
152}
153
154static struct kpp_alg dh = {
155	.set_secret = dh_set_secret,
156	.generate_public_key = dh_compute_value,
157	.compute_shared_secret = dh_compute_value,
158	.max_size = dh_max_size,
159	.exit = dh_exit_tfm,
160	.base = {
161		.cra_name = "dh",
162		.cra_driver_name = "dh-generic",
163		.cra_priority = 100,
164		.cra_module = THIS_MODULE,
165		.cra_ctxsize = sizeof(struct dh_ctx),
166	},
167};
168
169static int dh_init(void)
170{
171	return crypto_register_kpp(&dh);
172}
173
174static void dh_exit(void)
175{
176	crypto_unregister_kpp(&dh);
177}
178
179module_init(dh_init);
180module_exit(dh_exit);
181MODULE_ALIAS_CRYPTO("dh");
182MODULE_LICENSE("GPL");
183MODULE_DESCRIPTION("DH generic algorithm");