1 // SPDX-License-Identifier: GPL-2.0+ 2 /* 3 * Elliptic Curve (Russian) Digital Signature Algorithm for Cryptographic API 4 * 5 * Copyright (c) 2019 Vitaly Chikunov <vt@altlinux.org> 6 * 7 * References: 8 * GOST 34.10-2018, GOST R 34.10-2012, RFC 7091, ISO/IEC 14888-3:2018. 9 * 10 * Historical references: 11 * GOST R 34.10-2001, RFC 4357, ISO/IEC 14888-3:2006/Amd 1:2010. 12 * 13 * This program is free software; you can redistribute it and/or modify it 14 * under the terms of the GNU General Public License as published by the Free 15 * Software Foundation; either version 2 of the License, or (at your option) 16 * any later version. 17 */ 18 19 #include <linux/module.h> 20 #include <linux/crypto.h> 21 #include <crypto/streebog.h> 22 #include <crypto/internal/akcipher.h> 23 #include <crypto/akcipher.h> 24 #include <linux/oid_registry.h> 25 #include "ecrdsa_params.asn1.h" 26 #include "ecrdsa_pub_key.asn1.h" 27 #include "ecc.h" 28 #include "ecrdsa_defs.h" 29 30 #define ECRDSA_MAX_SIG_SIZE (2 * 512 / 8) 31 #define ECRDSA_MAX_DIGITS (512 / 64) 32 33 struct ecrdsa_ctx { 34 enum OID algo_oid; /* overall public key oid */ 35 enum OID curve_oid; /* parameter */ 36 enum OID digest_oid; /* parameter */ 37 const struct ecc_curve *curve; /* curve from oid */ 38 unsigned int digest_len; /* parameter (bytes) */ 39 const char *digest; /* digest name from oid */ 40 unsigned int key_len; /* @key length (bytes) */ 41 const char *key; /* raw public key */ 42 struct ecc_point pub_key; 43 u64 _pubp[2][ECRDSA_MAX_DIGITS]; /* point storage for @pub_key */ 44 }; 45 46 static const struct ecc_curve *get_curve_by_oid(enum OID oid) 47 { 48 switch (oid) { 49 case OID_gostCPSignA: 50 case OID_gostTC26Sign256B: 51 return &gost_cp256a; 52 case OID_gostCPSignB: 53 case OID_gostTC26Sign256C: 54 return &gost_cp256b; 55 case OID_gostCPSignC: 56 case OID_gostTC26Sign256D: 57 return &gost_cp256c; 58 case OID_gostTC26Sign512A: 59 return &gost_tc512a; 60 case OID_gostTC26Sign512B: 61 return &gost_tc512b; 62 /* The following two aren't implemented: */ 63 case OID_gostTC26Sign256A: 64 case OID_gostTC26Sign512C: 65 default: 66 return NULL; 67 } 68 } 69 70 static int ecrdsa_verify(struct akcipher_request *req) 71 { 72 struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req); 73 struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm); 74 unsigned char sig[ECRDSA_MAX_SIG_SIZE]; 75 unsigned char digest[STREEBOG512_DIGEST_SIZE]; 76 unsigned int ndigits = req->dst_len / sizeof(u64); 77 u64 r[ECRDSA_MAX_DIGITS]; /* witness (r) */ 78 u64 _r[ECRDSA_MAX_DIGITS]; /* -r */ 79 u64 s[ECRDSA_MAX_DIGITS]; /* second part of sig (s) */ 80 u64 e[ECRDSA_MAX_DIGITS]; /* h \mod q */ 81 u64 *v = e; /* e^{-1} \mod q */ 82 u64 z1[ECRDSA_MAX_DIGITS]; 83 u64 *z2 = _r; 84 struct ecc_point cc = ECC_POINT_INIT(s, e, ndigits); /* reuse s, e */ 85 86 /* 87 * Digest value, digest algorithm, and curve (modulus) should have the 88 * same length (256 or 512 bits), public key and signature should be 89 * twice bigger. 90 */ 91 if (!ctx->curve || 92 !ctx->digest || 93 !req->src || 94 !ctx->pub_key.x || 95 req->dst_len != ctx->digest_len || 96 req->dst_len != ctx->curve->g.ndigits * sizeof(u64) || 97 ctx->pub_key.ndigits != ctx->curve->g.ndigits || 98 req->dst_len * 2 != req->src_len || 99 WARN_ON(req->src_len > sizeof(sig)) || 100 WARN_ON(req->dst_len > sizeof(digest))) 101 return -EBADMSG; 102 103 sg_copy_to_buffer(req->src, sg_nents_for_len(req->src, req->src_len), 104 sig, req->src_len); 105 sg_pcopy_to_buffer(req->src, 106 sg_nents_for_len(req->src, 107 req->src_len + req->dst_len), 108 digest, req->dst_len, req->src_len); 109 110 vli_from_be64(s, sig, ndigits); 111 vli_from_be64(r, sig + ndigits * sizeof(u64), ndigits); 112 113 /* Step 1: verify that 0 < r < q, 0 < s < q */ 114 if (vli_is_zero(r, ndigits) || 115 vli_cmp(r, ctx->curve->n, ndigits) == 1 || 116 vli_is_zero(s, ndigits) || 117 vli_cmp(s, ctx->curve->n, ndigits) == 1) 118 return -EKEYREJECTED; 119 120 /* Step 2: calculate hash (h) of the message (passed as input) */ 121 /* Step 3: calculate e = h \mod q */ 122 vli_from_le64(e, digest, ndigits); 123 if (vli_cmp(e, ctx->curve->n, ndigits) == 1) 124 vli_sub(e, e, ctx->curve->n, ndigits); 125 if (vli_is_zero(e, ndigits)) 126 e[0] = 1; 127 128 /* Step 4: calculate v = e^{-1} \mod q */ 129 vli_mod_inv(v, e, ctx->curve->n, ndigits); 130 131 /* Step 5: calculate z_1 = sv \mod q, z_2 = -rv \mod q */ 132 vli_mod_mult_slow(z1, s, v, ctx->curve->n, ndigits); 133 vli_sub(_r, ctx->curve->n, r, ndigits); 134 vli_mod_mult_slow(z2, _r, v, ctx->curve->n, ndigits); 135 136 /* Step 6: calculate point C = z_1P + z_2Q, and R = x_c \mod q */ 137 ecc_point_mult_shamir(&cc, z1, &ctx->curve->g, z2, &ctx->pub_key, 138 ctx->curve); 139 if (vli_cmp(cc.x, ctx->curve->n, ndigits) == 1) 140 vli_sub(cc.x, cc.x, ctx->curve->n, ndigits); 141 142 /* Step 7: if R == r signature is valid */ 143 if (!vli_cmp(cc.x, r, ndigits)) 144 return 0; 145 else 146 return -EKEYREJECTED; 147 } 148 149 int ecrdsa_param_curve(void *context, size_t hdrlen, unsigned char tag, 150 const void *value, size_t vlen) 151 { 152 struct ecrdsa_ctx *ctx = context; 153 154 ctx->curve_oid = look_up_OID(value, vlen); 155 if (!ctx->curve_oid) 156 return -EINVAL; 157 ctx->curve = get_curve_by_oid(ctx->curve_oid); 158 return 0; 159 } 160 161 /* Optional. If present should match expected digest algo OID. */ 162 int ecrdsa_param_digest(void *context, size_t hdrlen, unsigned char tag, 163 const void *value, size_t vlen) 164 { 165 struct ecrdsa_ctx *ctx = context; 166 int digest_oid = look_up_OID(value, vlen); 167 168 if (digest_oid != ctx->digest_oid) 169 return -EINVAL; 170 return 0; 171 } 172 173 int ecrdsa_parse_pub_key(void *context, size_t hdrlen, unsigned char tag, 174 const void *value, size_t vlen) 175 { 176 struct ecrdsa_ctx *ctx = context; 177 178 ctx->key = value; 179 ctx->key_len = vlen; 180 return 0; 181 } 182 183 static u8 *ecrdsa_unpack_u32(u32 *dst, void *src) 184 { 185 memcpy(dst, src, sizeof(u32)); 186 return src + sizeof(u32); 187 } 188 189 /* Parse BER encoded subjectPublicKey. */ 190 static int ecrdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key, 191 unsigned int keylen) 192 { 193 struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm); 194 unsigned int ndigits; 195 u32 algo, paramlen; 196 u8 *params; 197 int err; 198 199 err = asn1_ber_decoder(&ecrdsa_pub_key_decoder, ctx, key, keylen); 200 if (err < 0) 201 return err; 202 203 /* Key parameters is in the key after keylen. */ 204 params = ecrdsa_unpack_u32(¶mlen, 205 ecrdsa_unpack_u32(&algo, (u8 *)key + keylen)); 206 207 if (algo == OID_gost2012PKey256) { 208 ctx->digest = "streebog256"; 209 ctx->digest_oid = OID_gost2012Digest256; 210 ctx->digest_len = 256 / 8; 211 } else if (algo == OID_gost2012PKey512) { 212 ctx->digest = "streebog512"; 213 ctx->digest_oid = OID_gost2012Digest512; 214 ctx->digest_len = 512 / 8; 215 } else 216 return -ENOPKG; 217 ctx->algo_oid = algo; 218 219 /* Parse SubjectPublicKeyInfo.AlgorithmIdentifier.parameters. */ 220 err = asn1_ber_decoder(&ecrdsa_params_decoder, ctx, params, paramlen); 221 if (err < 0) 222 return err; 223 /* 224 * Sizes of algo (set in digest_len) and curve should match 225 * each other. 226 */ 227 if (!ctx->curve || 228 ctx->curve->g.ndigits * sizeof(u64) != ctx->digest_len) 229 return -ENOPKG; 230 /* 231 * Key is two 256- or 512-bit coordinates which should match 232 * curve size. 233 */ 234 if ((ctx->key_len != (2 * 256 / 8) && 235 ctx->key_len != (2 * 512 / 8)) || 236 ctx->key_len != ctx->curve->g.ndigits * sizeof(u64) * 2) 237 return -ENOPKG; 238 239 ndigits = ctx->key_len / sizeof(u64) / 2; 240 ctx->pub_key = ECC_POINT_INIT(ctx->_pubp[0], ctx->_pubp[1], ndigits); 241 vli_from_le64(ctx->pub_key.x, ctx->key, ndigits); 242 vli_from_le64(ctx->pub_key.y, ctx->key + ndigits * sizeof(u64), 243 ndigits); 244 245 if (ecc_is_pubkey_valid_partial(ctx->curve, &ctx->pub_key)) 246 return -EKEYREJECTED; 247 248 return 0; 249 } 250 251 static unsigned int ecrdsa_max_size(struct crypto_akcipher *tfm) 252 { 253 struct ecrdsa_ctx *ctx = akcipher_tfm_ctx(tfm); 254 255 /* 256 * Verify doesn't need any output, so it's just informational 257 * for keyctl to determine the key bit size. 258 */ 259 return ctx->pub_key.ndigits * sizeof(u64); 260 } 261 262 static void ecrdsa_exit_tfm(struct crypto_akcipher *tfm) 263 { 264 } 265 266 static struct akcipher_alg ecrdsa_alg = { 267 .verify = ecrdsa_verify, 268 .set_pub_key = ecrdsa_set_pub_key, 269 .max_size = ecrdsa_max_size, 270 .exit = ecrdsa_exit_tfm, 271 .base = { 272 .cra_name = "ecrdsa", 273 .cra_driver_name = "ecrdsa-generic", 274 .cra_priority = 100, 275 .cra_module = THIS_MODULE, 276 .cra_ctxsize = sizeof(struct ecrdsa_ctx), 277 }, 278 }; 279 280 static int __init ecrdsa_mod_init(void) 281 { 282 return crypto_register_akcipher(&ecrdsa_alg); 283 } 284 285 static void __exit ecrdsa_mod_fini(void) 286 { 287 crypto_unregister_akcipher(&ecrdsa_alg); 288 } 289 290 module_init(ecrdsa_mod_init); 291 module_exit(ecrdsa_mod_fini); 292 293 MODULE_LICENSE("GPL"); 294 MODULE_AUTHOR("Vitaly Chikunov <vt@altlinux.org>"); 295 MODULE_DESCRIPTION("EC-RDSA generic algorithm"); 296 MODULE_ALIAS_CRYPTO("ecrdsa-generic"); 297