1 /* 2 * Copyright (c) 2021 Yubico AB. All rights reserved. 3 * Use of this source code is governed by a BSD-style 4 * license that can be found in the LICENSE file. 5 */ 6 7 /* 8 * Trusted Platform Module (TPM) 2.0 attestation support. Documentation 9 * references are relative to revision 01.38 of the TPM 2.0 specification. 10 */ 11 12 #include <openssl/sha.h> 13 14 #include "packed.h" 15 #include "fido.h" 16 17 /* Part 1, 4.89: TPM_GENERATED_VALUE */ 18 #define TPM_MAGIC 0xff544347 19 20 /* Part 2, 6.3: TPM_ALG_ID */ 21 #define TPM_ALG_RSA 0x0001 22 #define TPM_ALG_SHA256 0x000b 23 #define TPM_ALG_NULL 0x0010 24 #define TPM_ALG_ECC 0x0023 25 26 /* Part 2, 6.4: TPM_ECC_CURVE */ 27 #define TPM_ECC_P256 0x0003 28 29 /* Part 2, 6.9: TPM_ST_ATTEST_CERTIFY */ 30 #define TPM_ST_CERTIFY 0x8017 31 32 /* Part 2, 8.3: TPMA_OBJECT */ 33 #define TPMA_RESERVED 0xfff8f309 /* reserved bits; must be zero */ 34 #define TPMA_FIXED 0x00000002 /* object has fixed hierarchy */ 35 #define TPMA_CLEAR 0x00000004 /* object persists */ 36 #define TPMA_FIXED_P 0x00000010 /* object has fixed parent */ 37 #define TPMA_SENSITIVE 0x00000020 /* data originates within tpm */ 38 #define TPMA_SIGN 0x00040000 /* object may sign */ 39 40 /* Part 2, 10.4.2: TPM2B_DIGEST */ 41 PACKED_TYPE(tpm_sha256_digest_t, 42 struct tpm_sha256_digest { 43 uint16_t size; /* sizeof(body) */ 44 uint8_t body[32]; 45 }) 46 47 /* Part 2, 10.4.3: TPM2B_DATA */ 48 PACKED_TYPE(tpm_sha1_data_t, 49 struct tpm_sha1_data { 50 uint16_t size; /* sizeof(body */ 51 uint8_t body[20]; 52 }) 53 54 /* Part 2, 10.5.3: TPM2B_NAME */ 55 PACKED_TYPE(tpm_sha256_name_t, 56 struct tpm_sha256_name { 57 uint16_t size; /* sizeof(alg) + sizeof(body) */ 58 uint16_t alg; /* TPM_ALG_SHA256 */ 59 uint8_t body[32]; 60 }) 61 62 /* Part 2, 10.11.1: TPMS_CLOCK_INFO */ 63 PACKED_TYPE(tpm_clock_info_t, 64 struct tpm_clock_info { 65 uint64_t timestamp_ms; 66 uint32_t reset_count; /* obfuscated by tpm */ 67 uint32_t restart_count; /* obfuscated by tpm */ 68 uint8_t safe; /* 1 if timestamp_ms is current */ 69 }) 70 71 /* Part 2, 10.12.8 TPMS_ATTEST */ 72 PACKED_TYPE(tpm_sha1_attest_t, 73 struct tpm_sha1_attest { 74 uint32_t magic; /* TPM_MAGIC */ 75 uint16_t type; /* TPM_ST_ATTEST_CERTIFY */ 76 tpm_sha256_name_t signer; /* full tpm path of signing key */ 77 tpm_sha1_data_t data; /* signed sha1 */ 78 tpm_clock_info_t clock; 79 uint64_t fwversion; /* obfuscated by tpm */ 80 tpm_sha256_name_t name; /* sha256 of tpm_rs256_pubarea_t */ 81 tpm_sha256_name_t qual_name; /* full tpm path of attested key */ 82 }) 83 84 /* Part 2, 11.2.4.5: TPM2B_PUBLIC_KEY_RSA */ 85 PACKED_TYPE(tpm_rs256_key_t, 86 struct tpm_rs256_key { 87 uint16_t size; /* sizeof(body) */ 88 uint8_t body[256]; 89 }) 90 91 /* Part 2, 11.2.5.1: TPM2B_ECC_PARAMETER */ 92 PACKED_TYPE(tpm_es256_coord_t, 93 struct tpm_es256_coord { 94 uint16_t size; /* sizeof(body) */ 95 uint8_t body[32]; 96 }) 97 98 /* Part 2, 11.2.5.2: TPMS_ECC_POINT */ 99 PACKED_TYPE(tpm_es256_point_t, 100 struct tpm_es256_point { 101 tpm_es256_coord_t x; 102 tpm_es256_coord_t y; 103 }) 104 105 /* Part 2, 12.2.3.5: TPMS_RSA_PARMS */ 106 PACKED_TYPE(tpm_rs256_param_t, 107 struct tpm_rs256_param { 108 uint16_t symmetric; /* TPM_ALG_NULL */ 109 uint16_t scheme; /* TPM_ALG_NULL */ 110 uint16_t keybits; /* 2048 */ 111 uint32_t exponent; /* zero (meaning 2^16 + 1) */ 112 }) 113 114 /* Part 2, 12.2.3.6: TPMS_ECC_PARMS */ 115 PACKED_TYPE(tpm_es256_param_t, 116 struct tpm_es256_param { 117 uint16_t symmetric; /* TPM_ALG_NULL */ 118 uint16_t scheme; /* TPM_ALG_NULL */ 119 uint16_t curve_id; /* TPM_ECC_P256 */ 120 uint16_t kdf; /* TPM_ALG_NULL */ 121 }) 122 123 /* Part 2, 12.2.4: TPMT_PUBLIC */ 124 PACKED_TYPE(tpm_rs256_pubarea_t, 125 struct tpm_rs256_pubarea { 126 uint16_t alg; /* TPM_ALG_RSA */ 127 uint16_t hash; /* TPM_ALG_SHA256 */ 128 uint32_t attr; 129 tpm_sha256_digest_t policy; /* must be present? */ 130 tpm_rs256_param_t param; 131 tpm_rs256_key_t key; 132 }) 133 134 /* Part 2, 12.2.4: TPMT_PUBLIC */ 135 PACKED_TYPE(tpm_es256_pubarea_t, 136 struct tpm_es256_pubarea { 137 uint16_t alg; /* TPM_ALG_ECC */ 138 uint16_t hash; /* TPM_ALG_SHA256 */ 139 uint32_t attr; 140 tpm_sha256_digest_t policy; /* must be present? */ 141 tpm_es256_param_t param; 142 tpm_es256_point_t point; 143 }) 144 145 static int 146 get_signed_sha1(tpm_sha1_data_t *dgst, const fido_blob_t *authdata, 147 const fido_blob_t *clientdata) 148 { 149 const EVP_MD *md = NULL; 150 EVP_MD_CTX *ctx = NULL; 151 int ok = -1; 152 153 if ((dgst->size = sizeof(dgst->body)) != SHA_DIGEST_LENGTH || 154 (md = EVP_sha1()) == NULL || 155 (ctx = EVP_MD_CTX_new()) == NULL || 156 EVP_DigestInit_ex(ctx, md, NULL) != 1 || 157 EVP_DigestUpdate(ctx, authdata->ptr, authdata->len) != 1 || 158 EVP_DigestUpdate(ctx, clientdata->ptr, clientdata->len) != 1 || 159 EVP_DigestFinal_ex(ctx, dgst->body, NULL) != 1) { 160 fido_log_debug("%s: sha1", __func__); 161 goto fail; 162 } 163 164 ok = 0; 165 fail: 166 EVP_MD_CTX_free(ctx); 167 168 return (ok); 169 } 170 171 static int 172 get_signed_name(tpm_sha256_name_t *name, const fido_blob_t *pubarea) 173 { 174 name->alg = TPM_ALG_SHA256; 175 name->size = sizeof(name->alg) + sizeof(name->body); 176 if (sizeof(name->body) != SHA256_DIGEST_LENGTH || 177 SHA256(pubarea->ptr, pubarea->len, name->body) != name->body) { 178 fido_log_debug("%s: sha256", __func__); 179 return -1; 180 } 181 182 return 0; 183 } 184 185 static void 186 bswap_rs256_pubarea(tpm_rs256_pubarea_t *x) 187 { 188 x->alg = htobe16(x->alg); 189 x->hash = htobe16(x->hash); 190 x->attr = htobe32(x->attr); 191 x->policy.size = htobe16(x->policy.size); 192 x->param.symmetric = htobe16(x->param.symmetric); 193 x->param.scheme = htobe16(x->param.scheme); 194 x->param.keybits = htobe16(x->param.keybits); 195 x->key.size = htobe16(x->key.size); 196 } 197 198 static void 199 bswap_es256_pubarea(tpm_es256_pubarea_t *x) 200 { 201 x->alg = htobe16(x->alg); 202 x->hash = htobe16(x->hash); 203 x->attr = htobe32(x->attr); 204 x->policy.size = htobe16(x->policy.size); 205 x->param.symmetric = htobe16(x->param.symmetric); 206 x->param.scheme = htobe16(x->param.scheme); 207 x->param.curve_id = htobe16(x->param.curve_id); 208 x->param.kdf = htobe16(x->param.kdf); 209 x->point.x.size = htobe16(x->point.x.size); 210 x->point.y.size = htobe16(x->point.y.size); 211 } 212 213 static void 214 bswap_sha1_certinfo(tpm_sha1_attest_t *x) 215 { 216 x->magic = htobe32(x->magic); 217 x->type = htobe16(x->type); 218 x->signer.size = htobe16(x->signer.size); 219 x->data.size = htobe16(x->data.size); 220 x->name.alg = htobe16(x->name.alg); 221 x->name.size = htobe16(x->name.size); 222 } 223 224 static int 225 check_rs256_pubarea(const fido_blob_t *buf, const rs256_pk_t *pk) 226 { 227 const tpm_rs256_pubarea_t *actual; 228 tpm_rs256_pubarea_t expected; 229 int ok; 230 231 if (buf->len != sizeof(*actual)) { 232 fido_log_debug("%s: buf->len=%zu", __func__, buf->len); 233 return -1; 234 } 235 actual = (const void *)buf->ptr; 236 237 memset(&expected, 0, sizeof(expected)); 238 expected.alg = TPM_ALG_RSA; 239 expected.hash = TPM_ALG_SHA256; 240 expected.attr = be32toh(actual->attr); 241 expected.attr &= ~(TPMA_RESERVED|TPMA_CLEAR); 242 expected.attr |= (TPMA_FIXED|TPMA_FIXED_P|TPMA_SENSITIVE|TPMA_SIGN); 243 expected.policy = actual->policy; 244 expected.policy.size = sizeof(expected.policy.body); 245 expected.param.symmetric = TPM_ALG_NULL; 246 expected.param.scheme = TPM_ALG_NULL; 247 expected.param.keybits = 2048; 248 expected.param.exponent = 0; /* meaning 2^16+1 */ 249 expected.key.size = sizeof(expected.key.body); 250 memcpy(&expected.key.body, &pk->n, sizeof(expected.key.body)); 251 bswap_rs256_pubarea(&expected); 252 253 ok = timingsafe_bcmp(&expected, actual, sizeof(expected)); 254 explicit_bzero(&expected, sizeof(expected)); 255 256 return ok != 0 ? -1 : 0; 257 } 258 259 static int 260 check_es256_pubarea(const fido_blob_t *buf, const es256_pk_t *pk) 261 { 262 const tpm_es256_pubarea_t *actual; 263 tpm_es256_pubarea_t expected; 264 int ok; 265 266 if (buf->len != sizeof(*actual)) { 267 fido_log_debug("%s: buf->len=%zu", __func__, buf->len); 268 return -1; 269 } 270 actual = (const void *)buf->ptr; 271 272 memset(&expected, 0, sizeof(expected)); 273 expected.alg = TPM_ALG_ECC; 274 expected.hash = TPM_ALG_SHA256; 275 expected.attr = be32toh(actual->attr); 276 expected.attr &= ~(TPMA_RESERVED|TPMA_CLEAR); 277 expected.attr |= (TPMA_FIXED|TPMA_FIXED_P|TPMA_SENSITIVE|TPMA_SIGN); 278 expected.policy = actual->policy; 279 expected.policy.size = sizeof(expected.policy.body); 280 expected.param.symmetric = TPM_ALG_NULL; 281 expected.param.scheme = TPM_ALG_NULL; /* TCG Alg. Registry, 5.2.4 */ 282 expected.param.curve_id = TPM_ECC_P256; 283 expected.param.kdf = TPM_ALG_NULL; 284 expected.point.x.size = sizeof(expected.point.x.body); 285 expected.point.y.size = sizeof(expected.point.y.body); 286 memcpy(&expected.point.x.body, &pk->x, sizeof(expected.point.x.body)); 287 memcpy(&expected.point.y.body, &pk->y, sizeof(expected.point.y.body)); 288 bswap_es256_pubarea(&expected); 289 290 ok = timingsafe_bcmp(&expected, actual, sizeof(expected)); 291 explicit_bzero(&expected, sizeof(expected)); 292 293 return ok != 0 ? -1 : 0; 294 } 295 296 static int 297 check_sha1_certinfo(const fido_blob_t *buf, const fido_blob_t *clientdata_hash, 298 const fido_blob_t *authdata_raw, const fido_blob_t *pubarea) 299 { 300 const tpm_sha1_attest_t *actual; 301 tpm_sha1_attest_t expected; 302 tpm_sha1_data_t signed_data; 303 tpm_sha256_name_t signed_name; 304 int ok = -1; 305 306 memset(&signed_data, 0, sizeof(signed_data)); 307 memset(&signed_name, 0, sizeof(signed_name)); 308 309 if (get_signed_sha1(&signed_data, authdata_raw, clientdata_hash) < 0 || 310 get_signed_name(&signed_name, pubarea) < 0) { 311 fido_log_debug("%s: get_signed_sha1/name", __func__); 312 goto fail; 313 } 314 if (buf->len != sizeof(*actual)) { 315 fido_log_debug("%s: buf->len=%zu", __func__, buf->len); 316 goto fail; 317 } 318 actual = (const void *)buf->ptr; 319 320 memset(&expected, 0, sizeof(expected)); 321 expected.magic = TPM_MAGIC; 322 expected.type = TPM_ST_CERTIFY; 323 expected.signer = actual->signer; 324 expected.signer.size = sizeof(expected.signer.alg) + 325 sizeof(expected.signer.body); 326 expected.data = signed_data; 327 expected.clock = actual->clock; 328 expected.clock.safe = 1; 329 expected.fwversion = actual->fwversion; 330 expected.name = signed_name; 331 expected.qual_name = actual->qual_name; 332 bswap_sha1_certinfo(&expected); 333 334 ok = timingsafe_bcmp(&expected, actual, sizeof(expected)); 335 fail: 336 explicit_bzero(&expected, sizeof(expected)); 337 explicit_bzero(&signed_data, sizeof(signed_data)); 338 explicit_bzero(&signed_name, sizeof(signed_name)); 339 340 return ok != 0 ? -1 : 0; 341 } 342 343 int 344 fido_get_signed_hash_tpm(fido_blob_t *dgst, const fido_blob_t *clientdata_hash, 345 const fido_blob_t *authdata_raw, const fido_attstmt_t *attstmt, 346 const fido_attcred_t *attcred) 347 { 348 const fido_blob_t *pubarea = &attstmt->pubarea; 349 const fido_blob_t *certinfo = &attstmt->certinfo; 350 351 if (attstmt->alg != COSE_RS1) { 352 fido_log_debug("%s: unsupported alg %d", __func__, 353 attstmt->alg); 354 return -1; 355 } 356 357 switch (attcred->type) { 358 case COSE_ES256: 359 if (check_es256_pubarea(pubarea, &attcred->pubkey.es256) < 0) { 360 fido_log_debug("%s: check_es256_pubarea", __func__); 361 return -1; 362 } 363 break; 364 case COSE_RS256: 365 if (check_rs256_pubarea(pubarea, &attcred->pubkey.rs256) < 0) { 366 fido_log_debug("%s: check_rs256_pubarea", __func__); 367 return -1; 368 } 369 break; 370 default: 371 fido_log_debug("%s: unsupported type %d", __func__, 372 attcred->type); 373 return -1; 374 } 375 376 if (check_sha1_certinfo(certinfo, clientdata_hash, authdata_raw, 377 pubarea) < 0) { 378 fido_log_debug("%s: check_sha1_certinfo", __func__); 379 return -1; 380 } 381 382 if (dgst->len < SHA_DIGEST_LENGTH || 383 SHA1(certinfo->ptr, certinfo->len, dgst->ptr) != dgst->ptr) { 384 fido_log_debug("%s: sha1", __func__); 385 return -1; 386 } 387 dgst->len = SHA_DIGEST_LENGTH; 388 389 return 0; 390 } 391