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 Licence
  8 * as published by the Free Software Foundation; either version
  9 * 2 of the Licence, 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 inline void dh_clear_params(struct dh_ctx *ctx)
 25{
 26	mpi_free(ctx->p);
 27	mpi_free(ctx->g);
 28	ctx->p = NULL;
 29	ctx->g = NULL;
 30}
 31
 32static void dh_free_ctx(struct dh_ctx *ctx)
 33{
 34	dh_clear_params(ctx);
 35	mpi_free(ctx->xa);
 36	ctx->xa = NULL;
 37}
 38
 39/*
 40 * If base is g we compute the public key
 41 *	ya = g^xa mod p; [RFC2631 sec 2.1.1]
 42 * else if base if the counterpart public key we compute the shared secret
 43 *	ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
 44 */
 45static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
 46{
 47	/* val = base^xa mod p */
 48	return mpi_powm(val, base, ctx->xa, ctx->p);
 49}
 50
 51static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
 52{
 53	return kpp_tfm_ctx(tfm);
 54}
 55
 56static int dh_check_params_length(unsigned int p_len)
 57{
 58	return (p_len < 1536) ? -EINVAL : 0;
 59}
 60
 61static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
 62{
 63	if (unlikely(!params->p || !params->g))
 64		return -EINVAL;
 65
 66	if (dh_check_params_length(params->p_size << 3))
 67		return -EINVAL;
 68
 69	ctx->p = mpi_read_raw_data(params->p, params->p_size);
 70	if (!ctx->p)
 71		return -EINVAL;
 72
 73	ctx->g = mpi_read_raw_data(params->g, params->g_size);
 74	if (!ctx->g) {
 75		mpi_free(ctx->p);
 76		return -EINVAL;
 77	}
 78
 79	return 0;
 80}
 81
 82static int dh_set_secret(struct crypto_kpp *tfm, void *buf, unsigned int len)
 83{
 84	struct dh_ctx *ctx = dh_get_ctx(tfm);
 85	struct dh params;
 86
 87	if (crypto_dh_decode_key(buf, len, &params) < 0)
 88		return -EINVAL;
 89
 90	if (dh_set_params(ctx, &params) < 0)
 91		return -EINVAL;
 92
 93	ctx->xa = mpi_read_raw_data(params.key, params.key_size);
 94	if (!ctx->xa) {
 95		dh_clear_params(ctx);
 96		return -EINVAL;
 97	}
 98
 99	return 0;
100}
101
102static int dh_compute_value(struct kpp_request *req)
103{
104	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
105	struct dh_ctx *ctx = dh_get_ctx(tfm);
106	MPI base, val = mpi_alloc(0);
107	int ret = 0;
108	int sign;
109
110	if (!val)
111		return -ENOMEM;
112
113	if (unlikely(!ctx->xa)) {
114		ret = -EINVAL;
115		goto err_free_val;
116	}
117
118	if (req->src) {
119		base = mpi_read_raw_from_sgl(req->src, req->src_len);
120		if (!base) {
121			ret = -EINVAL;
122			goto err_free_val;
123		}
124	} else {
125		base = ctx->g;
126	}
127
128	ret = _compute_val(ctx, base, val);
129	if (ret)
130		goto err_free_base;
131
132	ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
133	if (ret)
134		goto err_free_base;
135
136	if (sign < 0)
137		ret = -EBADMSG;
138err_free_base:
139	if (req->src)
140		mpi_free(base);
141err_free_val:
142	mpi_free(val);
143	return ret;
144}
145
146static int dh_max_size(struct crypto_kpp *tfm)
147{
148	struct dh_ctx *ctx = dh_get_ctx(tfm);
149
150	return mpi_get_size(ctx->p);
151}
152
153static void dh_exit_tfm(struct crypto_kpp *tfm)
154{
155	struct dh_ctx *ctx = dh_get_ctx(tfm);
156
157	dh_free_ctx(ctx);
158}
159
160static struct kpp_alg dh = {
161	.set_secret = dh_set_secret,
162	.generate_public_key = dh_compute_value,
163	.compute_shared_secret = dh_compute_value,
164	.max_size = dh_max_size,
165	.exit = dh_exit_tfm,
166	.base = {
167		.cra_name = "dh",
168		.cra_driver_name = "dh-generic",
169		.cra_priority = 100,
170		.cra_module = THIS_MODULE,
171		.cra_ctxsize = sizeof(struct dh_ctx),
172	},
173};
174
175static int dh_init(void)
176{
177	return crypto_register_kpp(&dh);
178}
179
180static void dh_exit(void)
181{
182	crypto_unregister_kpp(&dh);
183}
184
185module_init(dh_init);
186module_exit(dh_exit);
187MODULE_ALIAS_CRYPTO("dh");
188MODULE_LICENSE("GPL");
189MODULE_DESCRIPTION("DH generic algorithm");