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 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
  18 struct dh_ctx {
  19         MPI p;
  20         MPI g;
  21         MPI xa;
  22 };
  23
  24 static 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
  32 static 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  */
  45 static 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
  51 static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm)
  52 {
  53         return kpp_tfm_ctx(tfm);
  54 }
  55
  56 static int dh_check_params_length(unsigned int p_len)
  57 {
  58         return (p_len < 1536) ? -EINVAL : 0;
  59 }
  60
  61 static 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
  82 static 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
 102 static 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;
 138 err_free_base:
 139         if (req->src)
 140                 mpi_free(base);
 141 err_free_val:
 142         mpi_free(val);
 143         return ret;
 144 }
 145
 146 static 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
 153 static 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
 160 static 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
 175 static int dh_init(void)
 176 {
 177         return crypto_register_kpp(&dh);
 178 }
 179
 180 static void dh_exit(void)
 181 {
 182         crypto_unregister_kpp(&dh);
 183 }
 184
 185 module_init(dh_init);
 186 module_exit(dh_exit);
 187 MODULE_ALIAS_CRYPTO("dh");
 188 MODULE_LICENSE("GPL");
 189 MODULE_DESCRIPTION("DH generic algorithm");