crypto/dh.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*  Diffie-Hellman Key Agreement Method [RFC2631]
   3  *
   4  * Copyright (c) 2016, Intel Corporation
   5  * Authors: Salvatore Benedetto <salvatore.benedetto@intel.com>
   6  */
   7
   8 #include <linux/module.h>
   9 #include <crypto/internal/kpp.h>
  10 #include <crypto/kpp.h>
  11 #include <crypto/dh.h>
  12 #include <linux/mpi.h>
  13
  14 struct dh_ctx {
  15         MPI p;  /* Value is guaranteed to be set. */
  16         MPI q;  /* Value is optional. */
  17         MPI g;  /* Value is guaranteed to be set. */
  18         MPI xa; /* Value is guaranteed to be set. */
  19 };
  20
  21 static void dh_clear_ctx(struct dh_ctx *ctx)
  22 {
  23         mpi_free(ctx->p);
  24         mpi_free(ctx->q);
  25         mpi_free(ctx->g);
  26         mpi_free(ctx->xa);
  27         memset(ctx, 0, sizeof(*ctx));
  28 }
  29
  30 /*
  31  * If base is g we compute the public key
  32  *      ya = g^xa mod p; [RFC2631 sec 2.1.1]
  33  * else if base if the counterpart public key we compute the shared secret
  34  *      ZZ = yb^xa mod p; [RFC2631 sec 2.1.1]
  35  */
  36 static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val)
  37 {
  38         /* val = base^xa mod p */
  39         return mpi_powm(val, base, ctx->xa, ctx->p);
  40 }
  41
  42 static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
  43 {
  44         return kpp_tfm_ctx(tfm);
  45 }
  46
  47 static int dh_check_params_length(unsigned int p_len)
  48 {
  49         return (p_len < 1536) ? -EINVAL : 0;
  50 }
  51
  52 static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
  53 {
  54         if (dh_check_params_length(params->p_size << 3))
  55                 return -EINVAL;
  56
  57         ctx->p = mpi_read_raw_data(params->p, params->p_size);
  58         if (!ctx->p)
  59                 return -EINVAL;
  60
  61         if (params->q && params->q_size) {
  62                 ctx->q = mpi_read_raw_data(params->q, params->q_size);
  63                 if (!ctx->q)
  64                         return -EINVAL;
  65         }
  66
  67         ctx->g = mpi_read_raw_data(params->g, params->g_size);
  68         if (!ctx->g)
  69                 return -EINVAL;
  70
  71         return 0;
  72 }
  73
  74 static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
  75                          unsigned int len)
  76 {
  77         struct dh_ctx *ctx = dh_get_ctx(tfm);
  78         struct dh params;
  79
  80         /* Free the old MPI key if any */
  81         dh_clear_ctx(ctx);
  82
  83         if (crypto_dh_decode_key(buf, len, &params) < 0)
  84                 goto err_clear_ctx;
  85
  86         if (dh_set_params(ctx, &params) < 0)
  87                 goto err_clear_ctx;
  88
  89         ctx->xa = mpi_read_raw_data(params.key, params.key_size);
  90         if (!ctx->xa)
  91                 goto err_clear_ctx;
  92
  93         return 0;
  94
  95 err_clear_ctx:
  96         dh_clear_ctx(ctx);
  97         return -EINVAL;
  98 }
  99
 100 /*
 101  * SP800-56A public key verification:
 102  *
 103  * * If Q is provided as part of the domain paramenters, a full validation
 104  *   according to SP800-56A section 5.6.2.3.1 is performed.
 105  *
 106  * * If Q is not provided, a partial validation according to SP800-56A section
 107  *   5.6.2.3.2 is performed.
 108  */
 109 static int dh_is_pubkey_valid(struct dh_ctx *ctx, MPI y)
 110 {
 111         if (unlikely(!ctx->p))
 112                 return -EINVAL;
 113
 114         /*
 115          * Step 1: Verify that 2 <= y <= p - 2.
 116          *
 117          * The upper limit check is actually y < p instead of y < p - 1
 118          * as the mpi_sub_ui function is yet missing.
 119          */
 120         if (mpi_cmp_ui(y, 1) < 1 || mpi_cmp(y, ctx->p) >= 0)
 121                 return -EINVAL;
 122
 123         /* Step 2: Verify that 1 = y^q mod p */
 124         if (ctx->q) {
 125                 MPI val = mpi_alloc(0);
 126                 int ret;
 127
 128                 if (!val)
 129                         return -ENOMEM;
 130
 131                 ret = mpi_powm(val, y, ctx->q, ctx->p);
 132
 133                 if (ret) {
 134                         mpi_free(val);
 135                         return ret;
 136                 }
 137
 138                 ret = mpi_cmp_ui(val, 1);
 139
 140                 mpi_free(val);
 141
 142                 if (ret != 0)
 143                         return -EINVAL;
 144         }
 145
 146         return 0;
 147 }
 148
 149 static int dh_compute_value(struct kpp_request *req)
 150 {
 151         struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
 152         struct dh_ctx *ctx = dh_get_ctx(tfm);
 153         MPI base, val = mpi_alloc(0);
 154         int ret = 0;
 155         int sign;
 156
 157         if (!val)
 158                 return -ENOMEM;
 159
 160         if (unlikely(!ctx->xa)) {
 161                 ret = -EINVAL;
 162                 goto err_free_val;
 163         }
 164
 165         if (req->src) {
 166                 base = mpi_read_raw_from_sgl(req->src, req->src_len);
 167                 if (!base) {
 168                         ret = -EINVAL;
 169                         goto err_free_val;
 170                 }
 171                 ret = dh_is_pubkey_valid(ctx, base);
 172                 if (ret)
 173                         goto err_free_base;
 174         } else {
 175                 base = ctx->g;
 176         }
 177
 178         ret = _compute_val(ctx, base, val);
 179         if (ret)
 180                 goto err_free_base;
 181
 182         ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
 183         if (ret)
 184                 goto err_free_base;
 185
 186         if (sign < 0)
 187                 ret = -EBADMSG;
 188 err_free_base:
 189         if (req->src)
 190                 mpi_free(base);
 191 err_free_val:
 192         mpi_free(val);
 193         return ret;
 194 }
 195
 196 static unsigned int dh_max_size(struct crypto_kpp *tfm)
 197 {
 198         struct dh_ctx *ctx = dh_get_ctx(tfm);
 199
 200         return mpi_get_size(ctx->p);
 201 }
 202
 203 static void dh_exit_tfm(struct crypto_kpp *tfm)
 204 {
 205         struct dh_ctx *ctx = dh_get_ctx(tfm);
 206
 207         dh_clear_ctx(ctx);
 208 }
 209
 210 static struct kpp_alg dh = {
 211         .set_secret = dh_set_secret,
 212         .generate_public_key = dh_compute_value,
 213         .compute_shared_secret = dh_compute_value,
 214         .max_size = dh_max_size,
 215         .exit = dh_exit_tfm,
 216         .base = {
 217                 .cra_name = "dh",
 218                 .cra_driver_name = "dh-generic",
 219                 .cra_priority = 100,
 220                 .cra_module = THIS_MODULE,
 221                 .cra_ctxsize = sizeof(struct dh_ctx),
 222         },
 223 };
 224
 225 static int dh_init(void)
 226 {
 227         return crypto_register_kpp(&dh);
 228 }
 229
 230 static void dh_exit(void)
 231 {
 232         crypto_unregister_kpp(&dh);
 233 }
 234
 235 subsys_initcall(dh_init);
 236 module_exit(dh_exit);
 237 MODULE_ALIAS_CRYPTO("dh");
 238 MODULE_LICENSE("GPL");
 239 MODULE_DESCRIPTION("DH generic algorithm");