linux/crypto/dh.c
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   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");
 190