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; /* Value is guaranteed to be set. */ 20 MPI q; /* Value is optional. */ 21 MPI g; /* Value is guaranteed to be set. */ 22 MPI xa; /* Value is guaranteed to be set. */ 23 }; 24 25 static void dh_clear_ctx(struct dh_ctx *ctx) 26 { 27 mpi_free(ctx->p); 28 mpi_free(ctx->q); 29 mpi_free(ctx->g); 30 mpi_free(ctx->xa); 31 memset(ctx, 0, sizeof(*ctx)); 32 } 33 34 /* 35 * If base is g we compute the public key 36 * ya = g^xa mod p; [RFC2631 sec 2.1.1] 37 * else if base if the counterpart public key we compute the shared secret 38 * ZZ = yb^xa mod p; [RFC2631 sec 2.1.1] 39 */ 40 static int _compute_val(const struct dh_ctx *ctx, MPI base, MPI val) 41 { 42 /* val = base^xa mod p */ 43 return mpi_powm(val, base, ctx->xa, ctx->p); 44 } 45 46 static inline struct dh_ctx *dh_get_ctx(struct crypto_kpp *tfm) 47 { 48 return kpp_tfm_ctx(tfm); 49 } 50 51 static int dh_check_params_length(unsigned int p_len) 52 { 53 return (p_len < 1536) ? -EINVAL : 0; 54 } 55 56 static int dh_set_params(struct dh_ctx *ctx, struct dh *params) 57 { 58 if (dh_check_params_length(params->p_size << 3)) 59 return -EINVAL; 60 61 ctx->p = mpi_read_raw_data(params->p, params->p_size); 62 if (!ctx->p) 63 return -EINVAL; 64 65 if (params->q && params->q_size) { 66 ctx->q = mpi_read_raw_data(params->q, params->q_size); 67 if (!ctx->q) 68 return -EINVAL; 69 } 70 71 ctx->g = mpi_read_raw_data(params->g, params->g_size); 72 if (!ctx->g) 73 return -EINVAL; 74 75 return 0; 76 } 77 78 static int dh_set_secret(struct crypto_kpp *tfm, const void *buf, 79 unsigned int len) 80 { 81 struct dh_ctx *ctx = dh_get_ctx(tfm); 82 struct dh params; 83 84 /* Free the old MPI key if any */ 85 dh_clear_ctx(ctx); 86 87 if (crypto_dh_decode_key(buf, len, ¶ms) < 0) 88 goto err_clear_ctx; 89 90 if (dh_set_params(ctx, ¶ms) < 0) 91 goto err_clear_ctx; 92 93 ctx->xa = mpi_read_raw_data(params.key, params.key_size); 94 if (!ctx->xa) 95 goto err_clear_ctx; 96 97 return 0; 98 99 err_clear_ctx: 100 dh_clear_ctx(ctx); 101 return -EINVAL; 102 } 103 104 /* 105 * SP800-56A public key verification: 106 * 107 * * If Q is provided as part of the domain paramenters, a full validation 108 * according to SP800-56A section 5.6.2.3.1 is performed. 109 * 110 * * If Q is not provided, a partial validation according to SP800-56A section 111 * 5.6.2.3.2 is performed. 112 */ 113 static int dh_is_pubkey_valid(struct dh_ctx *ctx, MPI y) 114 { 115 if (unlikely(!ctx->p)) 116 return -EINVAL; 117 118 /* 119 * Step 1: Verify that 2 <= y <= p - 2. 120 * 121 * The upper limit check is actually y < p instead of y < p - 1 122 * as the mpi_sub_ui function is yet missing. 123 */ 124 if (mpi_cmp_ui(y, 1) < 1 || mpi_cmp(y, ctx->p) >= 0) 125 return -EINVAL; 126 127 /* Step 2: Verify that 1 = y^q mod p */ 128 if (ctx->q) { 129 MPI val = mpi_alloc(0); 130 int ret; 131 132 if (!val) 133 return -ENOMEM; 134 135 ret = mpi_powm(val, y, ctx->q, ctx->p); 136 137 if (ret) { 138 mpi_free(val); 139 return ret; 140 } 141 142 ret = mpi_cmp_ui(val, 1); 143 144 mpi_free(val); 145 146 if (ret != 0) 147 return -EINVAL; 148 } 149 150 return 0; 151 } 152 153 static int dh_compute_value(struct kpp_request *req) 154 { 155 struct crypto_kpp *tfm = crypto_kpp_reqtfm(req); 156 struct dh_ctx *ctx = dh_get_ctx(tfm); 157 MPI base, val = mpi_alloc(0); 158 int ret = 0; 159 int sign; 160 161 if (!val) 162 return -ENOMEM; 163 164 if (unlikely(!ctx->xa)) { 165 ret = -EINVAL; 166 goto err_free_val; 167 } 168 169 if (req->src) { 170 base = mpi_read_raw_from_sgl(req->src, req->src_len); 171 if (!base) { 172 ret = -EINVAL; 173 goto err_free_val; 174 } 175 ret = dh_is_pubkey_valid(ctx, base); 176 if (ret) 177 goto err_free_base; 178 } else { 179 base = ctx->g; 180 } 181 182 ret = _compute_val(ctx, base, val); 183 if (ret) 184 goto err_free_base; 185 186 ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign); 187 if (ret) 188 goto err_free_base; 189 190 if (sign < 0) 191 ret = -EBADMSG; 192 err_free_base: 193 if (req->src) 194 mpi_free(base); 195 err_free_val: 196 mpi_free(val); 197 return ret; 198 } 199 200 static unsigned int dh_max_size(struct crypto_kpp *tfm) 201 { 202 struct dh_ctx *ctx = dh_get_ctx(tfm); 203 204 return mpi_get_size(ctx->p); 205 } 206 207 static void dh_exit_tfm(struct crypto_kpp *tfm) 208 { 209 struct dh_ctx *ctx = dh_get_ctx(tfm); 210 211 dh_clear_ctx(ctx); 212 } 213 214 static struct kpp_alg dh = { 215 .set_secret = dh_set_secret, 216 .generate_public_key = dh_compute_value, 217 .compute_shared_secret = dh_compute_value, 218 .max_size = dh_max_size, 219 .exit = dh_exit_tfm, 220 .base = { 221 .cra_name = "dh", 222 .cra_driver_name = "dh-generic", 223 .cra_priority = 100, 224 .cra_module = THIS_MODULE, 225 .cra_ctxsize = sizeof(struct dh_ctx), 226 }, 227 }; 228 229 static int dh_init(void) 230 { 231 return crypto_register_kpp(&dh); 232 } 233 234 static void dh_exit(void) 235 { 236 crypto_unregister_kpp(&dh); 237 } 238 239 module_init(dh_init); 240 module_exit(dh_exit); 241 MODULE_ALIAS_CRYPTO("dh"); 242 MODULE_LICENSE("GPL"); 243 MODULE_DESCRIPTION("DH generic algorithm"); 244