crypto/ecrdsa.c

   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  10  * Historical references: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(&paramlen,
 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");