1 /* Diffie-Hellman Key Agreement Method [RFC2631]
3 * Copyright (c) 2016, Intel Corporation
4 * Authors: Salvatore Benedetto <salvatore.benedetto@intel.com>
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.
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>
19 MPI p; /* Value is guaranteed to be set. */
20 MPI q; /* Value is optional. */
21 MPI g; /* Value is guaranteed to be set. */
22 MPI xa; /* Value is guaranteed to be set. */
25 static void dh_clear_ctx(struct dh_ctx *ctx)
31 memset(ctx, 0, sizeof(*ctx));
35 * If base is g we compute the public key
36 * ya = g^xa mod p; [RFC2631 sec 2.1.1]
37 * else if base if the counterpart public key we compute the shared secret
38 * ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
40 static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
42 /* val = base^xa mod p */
43 return mpi_powm(val, base, ctx->xa, ctx->p);
46 static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
48 return kpp_tfm_ctx(tfm);
51 static int dh_check_params_length(unsigned int p_len)
53 return (p_len < 1536) ? -EINVAL : 0;
56 static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
58 if (dh_check_params_length(params->p_size << 3))
61 ctx->p = mpi_read_raw_data(params->p, params->p_size);
65 if (params->q && params->q_size) {
66 ctx->q = mpi_read_raw_data(params->q, params->q_size);
71 ctx->g = mpi_read_raw_data(params->g, params->g_size);
78 static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
81 struct dh_ctx *ctx = dh_get_ctx(tfm);
84 /* Free the old MPI key if any */
87 if (crypto_dh_decode_key(buf, len, ¶ms) < 0)
90 if (dh_set_params(ctx, ¶ms) < 0)
93 ctx->xa = mpi_read_raw_data(params.key, params.key_size);
105 * SP800-56A public key verification:
107 * * If Q is provided as part of the domain paramenters, a full validation
108 * according to SP800-56A section 5.6.2.3.1 is performed.
110 * * If Q is not provided, a partial validation according to SP800-56A section
111 * 5.6.2.3.2 is performed.
113 static int dh_is_pubkey_valid(struct dh_ctx *ctx, MPI y)
115 if (unlikely(!ctx->p))
119 * Step 1: Verify that 2 <= y <= p - 2.
121 * The upper limit check is actually y < p instead of y < p - 1
122 * as the mpi_sub_ui function is yet missing.
124 if (mpi_cmp_ui(y, 1) < 1 || mpi_cmp(y, ctx->p) >= 0)
127 /* Step 2: Verify that 1 = y^q mod p */
129 MPI val = mpi_alloc(0);
135 ret = mpi_powm(val, y, ctx->q, ctx->p);
142 ret = mpi_cmp_ui(val, 1);
153 static int dh_compute_value(struct kpp_request *req)
155 struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
156 struct dh_ctx *ctx = dh_get_ctx(tfm);
157 MPI base, val = mpi_alloc(0);
164 if (unlikely(!ctx->xa)) {
170 base = mpi_read_raw_from_sgl(req->src, req->src_len);
175 ret = dh_is_pubkey_valid(ctx, base);
182 ret = _compute_val(ctx, base, val);
186 ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
200 static unsigned int dh_max_size(struct crypto_kpp *tfm)
202 struct dh_ctx *ctx = dh_get_ctx(tfm);
204 return mpi_get_size(ctx->p);
207 static void dh_exit_tfm(struct crypto_kpp *tfm)
209 struct dh_ctx *ctx = dh_get_ctx(tfm);
214 static struct kpp_alg dh = {
215 .set_secret = dh_set_secret,
216 .generate_public_key = dh_compute_value,
217 .compute_shared_secret = dh_compute_value,
218 .max_size = dh_max_size,
222 .cra_driver_name = "dh-generic",
224 .cra_module = THIS_MODULE,
225 .cra_ctxsize = sizeof(struct dh_ctx),
229 static int dh_init(void)
231 return crypto_register_kpp(&dh);
234 static void dh_exit(void)
236 crypto_unregister_kpp(&dh);
239 module_init(dh_init);
240 module_exit(dh_exit);
241 MODULE_ALIAS_CRYPTO("dh");
242 MODULE_LICENSE("GPL");
243 MODULE_DESCRIPTION("DH generic algorithm");