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