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 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, const void *buf, 83 unsigned int len) 84 { 85 struct dh_ctx *ctx = dh_get_ctx(tfm); 86 struct dh params; 87 88 /* Free the old MPI key if any */ 89 dh_free_ctx(ctx); 90 91 if (crypto_dh_decode_key(buf, len, ¶ms) < 0) 92 return -EINVAL; 93 94 if (dh_set_params(ctx, ¶ms) < 0) 95 return -EINVAL; 96 97 ctx->xa = mpi_read_raw_data(params.key, params.key_size); 98 if (!ctx->xa) { 99 dh_clear_params(ctx); 100 return -EINVAL; 101 } 102 103 return 0; 104 } 105 106 static int dh_compute_value(struct kpp_request *req) 107 { 108 struct crypto_kpp *tfm = crypto_kpp_reqtfm(req); 109 struct dh_ctx *ctx = dh_get_ctx(tfm); 110 MPI base, val = mpi_alloc(0); 111 int ret = 0; 112 int sign; 113 114 if (!val) 115 return -ENOMEM; 116 117 if (unlikely(!ctx->xa)) { 118 ret = -EINVAL; 119 goto err_free_val; 120 } 121 122 if (req->src) { 123 base = mpi_read_raw_from_sgl(req->src, req->src_len); 124 if (!base) { 125 ret = -EINVAL; 126 goto err_free_val; 127 } 128 } else { 129 base = ctx->g; 130 } 131 132 ret = _compute_val(ctx, base, val); 133 if (ret) 134 goto err_free_base; 135 136 ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign); 137 if (ret) 138 goto err_free_base; 139 140 if (sign < 0) 141 ret = -EBADMSG; 142 err_free_base: 143 if (req->src) 144 mpi_free(base); 145 err_free_val: 146 mpi_free(val); 147 return ret; 148 } 149 150 static unsigned int dh_max_size(struct crypto_kpp *tfm) 151 { 152 struct dh_ctx *ctx = dh_get_ctx(tfm); 153 154 return mpi_get_size(ctx->p); 155 } 156 157 static void dh_exit_tfm(struct crypto_kpp *tfm) 158 { 159 struct dh_ctx *ctx = dh_get_ctx(tfm); 160 161 dh_free_ctx(ctx); 162 } 163 164 static struct kpp_alg dh = { 165 .set_secret = dh_set_secret, 166 .generate_public_key = dh_compute_value, 167 .compute_shared_secret = dh_compute_value, 168 .max_size = dh_max_size, 169 .exit = dh_exit_tfm, 170 .base = { 171 .cra_name = "dh", 172 .cra_driver_name = "dh-generic", 173 .cra_priority = 100, 174 .cra_module = THIS_MODULE, 175 .cra_ctxsize = sizeof(struct dh_ctx), 176 }, 177 }; 178 179 static int dh_init(void) 180 { 181 return crypto_register_kpp(&dh); 182 } 183 184 static void dh_exit(void) 185 { 186 crypto_unregister_kpp(&dh); 187 } 188 189 module_init(dh_init); 190 module_exit(dh_exit); 191 MODULE_ALIAS_CRYPTO("dh"); 192 MODULE_LICENSE("GPL"); 193 MODULE_DESCRIPTION("DH generic algorithm"); 194