1 /* ECDH key-agreement protocol 2 * 3 * Copyright (c) 2016, Intel Corporation 4 * Authors: Salvator 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/ecdh.h> 16 #include <linux/scatterlist.h> 17 #include "ecc.h" 18 19 struct ecdh_ctx { 20 unsigned int curve_id; 21 unsigned int ndigits; 22 u64 private_key[ECC_MAX_DIGITS]; 23 }; 24 25 static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm) 26 { 27 return kpp_tfm_ctx(tfm); 28 } 29 30 static unsigned int ecdh_supported_curve(unsigned int curve_id) 31 { 32 switch (curve_id) { 33 case ECC_CURVE_NIST_P192: return ECC_CURVE_NIST_P192_DIGITS; 34 case ECC_CURVE_NIST_P256: return ECC_CURVE_NIST_P256_DIGITS; 35 default: return 0; 36 } 37 } 38 39 static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf, 40 unsigned int len) 41 { 42 struct ecdh_ctx *ctx = ecdh_get_ctx(tfm); 43 struct ecdh params; 44 unsigned int ndigits; 45 46 if (crypto_ecdh_decode_key(buf, len, ¶ms) < 0) 47 return -EINVAL; 48 49 ndigits = ecdh_supported_curve(params.curve_id); 50 if (!ndigits) 51 return -EINVAL; 52 53 ctx->curve_id = params.curve_id; 54 ctx->ndigits = ndigits; 55 56 if (!params.key || !params.key_size) 57 return ecc_gen_privkey(ctx->curve_id, ctx->ndigits, 58 ctx->private_key); 59 60 if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits, 61 (const u64 *)params.key, params.key_size) < 0) 62 return -EINVAL; 63 64 memcpy(ctx->private_key, params.key, params.key_size); 65 66 return 0; 67 } 68 69 static int ecdh_compute_value(struct kpp_request *req) 70 { 71 struct crypto_kpp *tfm = crypto_kpp_reqtfm(req); 72 struct ecdh_ctx *ctx = ecdh_get_ctx(tfm); 73 u64 *public_key; 74 u64 *shared_secret = NULL; 75 void *buf; 76 size_t copied, nbytes, public_key_sz; 77 int ret = -ENOMEM; 78 79 nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT; 80 /* Public part is a point thus it has both coordinates */ 81 public_key_sz = 2 * nbytes; 82 83 public_key = kmalloc(public_key_sz, GFP_KERNEL); 84 if (!public_key) 85 return -ENOMEM; 86 87 if (req->src) { 88 shared_secret = kmalloc(nbytes, GFP_KERNEL); 89 if (!shared_secret) 90 goto free_pubkey; 91 92 /* from here on it's invalid parameters */ 93 ret = -EINVAL; 94 95 /* must have exactly two points to be on the curve */ 96 if (public_key_sz != req->src_len) 97 goto free_all; 98 99 copied = sg_copy_to_buffer(req->src, 100 sg_nents_for_len(req->src, 101 public_key_sz), 102 public_key, public_key_sz); 103 if (copied != public_key_sz) 104 goto free_all; 105 106 ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits, 107 ctx->private_key, public_key, 108 shared_secret); 109 110 buf = shared_secret; 111 } else { 112 ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits, 113 ctx->private_key, public_key); 114 buf = public_key; 115 nbytes = public_key_sz; 116 } 117 118 if (ret < 0) 119 goto free_all; 120 121 /* might want less than we've got */ 122 nbytes = min_t(size_t, nbytes, req->dst_len); 123 copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst, 124 nbytes), 125 buf, nbytes); 126 if (copied != nbytes) 127 ret = -EINVAL; 128 129 /* fall through */ 130 free_all: 131 kzfree(shared_secret); 132 free_pubkey: 133 kfree(public_key); 134 return ret; 135 } 136 137 static unsigned int ecdh_max_size(struct crypto_kpp *tfm) 138 { 139 struct ecdh_ctx *ctx = ecdh_get_ctx(tfm); 140 141 /* Public key is made of two coordinates, add one to the left shift */ 142 return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1); 143 } 144 145 static struct kpp_alg ecdh = { 146 .set_secret = ecdh_set_secret, 147 .generate_public_key = ecdh_compute_value, 148 .compute_shared_secret = ecdh_compute_value, 149 .max_size = ecdh_max_size, 150 .base = { 151 .cra_name = "ecdh", 152 .cra_driver_name = "ecdh-generic", 153 .cra_priority = 100, 154 .cra_module = THIS_MODULE, 155 .cra_ctxsize = sizeof(struct ecdh_ctx), 156 }, 157 }; 158 159 static int ecdh_init(void) 160 { 161 return crypto_register_kpp(&ecdh); 162 } 163 164 static void ecdh_exit(void) 165 { 166 crypto_unregister_kpp(&ecdh); 167 } 168 169 module_init(ecdh_init); 170 module_exit(ecdh_exit); 171 MODULE_ALIAS_CRYPTO("ecdh"); 172 MODULE_LICENSE("GPL"); 173 MODULE_DESCRIPTION("ECDH generic algorithm"); 174