crypto/dh.c

   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
  18 struct dh_ctx {
  19         MPI p;
  20         MPI g;
  21         MPI xa;
  22 };
  23
  24 static 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  */
  38 static 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
  44 static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
  45 {
  46         return kpp_tfm_ctx(tfm);
  47 }
  48
  49 static int dh_check_params_length(unsigned int p_len)
  50 {
  51         return (p_len < 1536) ? -EINVAL : 0;
  52 }
  53
  54 static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
  55 {
  56         if (unlikely(!params->p || !params->g))
  57                 return -EINVAL;
  58
  59         if (dh_check_params_length(params->p_size << 3))
  60                 return -EINVAL;
  61
  62         ctx->p = mpi_read_raw_data(params->p, params->p_size);
  63         if (!ctx->p)
  64                 return -EINVAL;
  65
  66         ctx->g = mpi_read_raw_data(params->g, params->g_size);
  67         if (!ctx->g)
  68                 return -EINVAL;
  69
  70         return 0;
  71 }
  72
  73 static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
  74                          unsigned int len)
  75 {
  76         struct dh_ctx *ctx = dh_get_ctx(tfm);
  77         struct dh params;
  78
  79         /* Free the old MPI key if any */
  80         dh_clear_ctx(ctx);
  81
  82         if (crypto_dh_decode_key(buf, len, &params) < 0)
  83                 goto err_clear_ctx;
  84
  85         if (dh_set_params(ctx, &params) < 0)
  86                 goto err_clear_ctx;
  87
  88         ctx->xa = mpi_read_raw_data(params.key, params.key_size);
  89         if (!ctx->xa)
  90                 goto err_clear_ctx;
  91
  92         return 0;
  93
  94 err_clear_ctx:
  95         dh_clear_ctx(ctx);
  96         return -EINVAL;
  97 }
  98
  99 static int dh_compute_value(struct kpp_request *req)
 100 {
 101         struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
 102         struct dh_ctx *ctx = dh_get_ctx(tfm);
 103         MPI base, val = mpi_alloc(0);
 104         int ret = 0;
 105         int sign;
 106
 107         if (!val)
 108                 return -ENOMEM;
 109
 110         if (unlikely(!ctx->xa)) {
 111                 ret = -EINVAL;
 112                 goto err_free_val;
 113         }
 114
 115         if (req->src) {
 116                 base = mpi_read_raw_from_sgl(req->src, req->src_len);
 117                 if (!base) {
 118                         ret = -EINVAL;
 119                         goto err_free_val;
 120                 }
 121         } else {
 122                 base = ctx->g;
 123         }
 124
 125         ret = _compute_val(ctx, base, val);
 126         if (ret)
 127                 goto err_free_base;
 128
 129         ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
 130         if (ret)
 131                 goto err_free_base;
 132
 133         if (sign < 0)
 134                 ret = -EBADMSG;
 135 err_free_base:
 136         if (req->src)
 137                 mpi_free(base);
 138 err_free_val:
 139         mpi_free(val);
 140         return ret;
 141 }
 142
 143 static unsigned int dh_max_size(struct crypto_kpp *tfm)
 144 {
 145         struct dh_ctx *ctx = dh_get_ctx(tfm);
 146
 147         return mpi_get_size(ctx->p);
 148 }
 149
 150 static void dh_exit_tfm(struct crypto_kpp *tfm)
 151 {
 152         struct dh_ctx *ctx = dh_get_ctx(tfm);
 153
 154         dh_clear_ctx(ctx);
 155 }
 156
 157 static struct kpp_alg dh = {
 158         .set_secret = dh_set_secret,
 159         .generate_public_key = dh_compute_value,
 160         .compute_shared_secret = dh_compute_value,
 161         .max_size = dh_max_size,
 162         .exit = dh_exit_tfm,
 163         .base = {
 164                 .cra_name = "dh",
 165                 .cra_driver_name = "dh-generic",
 166                 .cra_priority = 100,
 167                 .cra_module = THIS_MODULE,
 168                 .cra_ctxsize = sizeof(struct dh_ctx),
 169         },
 170 };
 171
 172 static int dh_init(void)
 173 {
 174         return crypto_register_kpp(&dh);
 175 }
 176
 177 static void dh_exit(void)
 178 {
 179         crypto_unregister_kpp(&dh);
 180 }
 181
 182 module_init(dh_init);
 183 module_exit(dh_exit);
 184 MODULE_ALIAS_CRYPTO("dh");
 185 MODULE_LICENSE("GPL");
 186 MODULE_DESCRIPTION("DH generic algorithm");