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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 | 19 | #define TPM_MAGIC 0xff544347 |
19 | | |
20 | | /* Part 2, 6.3: TPM_ALG_ID */ |
21 | 28 | #define TPM_ALG_RSA 0x0001 |
22 | 49 | #define TPM_ALG_SHA256 0x000b |
23 | 56 | #define TPM_ALG_NULL 0x0010 |
24 | | |
25 | | /* Part 2, 6.9: TPM_ST_ATTEST_CERTIFY */ |
26 | 19 | #define TPM_ST_CERTIFY 0x8017 |
27 | | |
28 | | /* Part 2, 8.3: TPMA_OBJECT */ |
29 | 28 | #define TPMA_RESERVED 0xfff8f309 /* reserved bits; must be zero */ |
30 | 28 | #define TPMA_FIXED 0x00000002 /* object has fixed hierarchy */ |
31 | 28 | #define TPMA_CLEAR 0x00000004 /* object persists */ |
32 | 28 | #define TPMA_FIXED_P 0x00000010 /* object has fixed parent */ |
33 | 28 | #define TPMA_SENSITIVE 0x00000020 /* data originates within tpm */ |
34 | 28 | #define TPMA_SIGN 0x00020000 /* object may sign */ |
35 | | |
36 | | /* Part 2, 10.4.2: TPM2B_DIGEST */ |
37 | | PACKED_TYPE(tpm_sha256_digest_t, |
38 | | struct tpm_sha256_digest { |
39 | | uint16_t size; /* sizeof(body) */ |
40 | | uint8_t body[32]; |
41 | | }) |
42 | | |
43 | | /* Part 2, 10.4.3: TPM2B_DATA */ |
44 | | PACKED_TYPE(tpm_sha1_data_t, |
45 | | struct tpm_sha1_data { |
46 | | uint16_t size; /* sizeof(body */ |
47 | | uint8_t body[20]; |
48 | | }) |
49 | | |
50 | | /* Part 2, 10.5.3: TPM2B_NAME */ |
51 | | PACKED_TYPE(tpm_sha256_name_t, |
52 | | struct tpm_sha256_name { |
53 | | uint16_t size; /* sizeof(alg) + sizeof(body) */ |
54 | | uint16_t alg; /* TPM_ALG_SHA256 */ |
55 | | uint8_t body[32]; |
56 | | }) |
57 | | |
58 | | /* Part 2, 10.11.1: TPMS_CLOCK_INFO */ |
59 | | PACKED_TYPE(tpm_clock_info_t, |
60 | | struct tpm_clock_info { |
61 | | uint64_t timestamp_ms; |
62 | | uint32_t reset_count; /* obfuscated by tpm */ |
63 | | uint32_t restart_count; /* obfuscated by tpm */ |
64 | | uint8_t safe; /* 1 if timestamp_ms is current */ |
65 | | }) |
66 | | |
67 | | /* Part 2, 10.12.8 TPMS_ATTEST */ |
68 | | PACKED_TYPE(tpm_sha1_attest_t, |
69 | | struct tpm_sha1_attest { |
70 | | uint32_t magic; /* TPM_MAGIC */ |
71 | | uint16_t type; /* TPM_ST_ATTEST_CERTIFY */ |
72 | | tpm_sha256_name_t signer; /* full tpm path of signing key */ |
73 | | tpm_sha1_data_t data; /* signed sha1 */ |
74 | | tpm_clock_info_t clock; |
75 | | uint64_t fwversion; /* obfuscated by tpm */ |
76 | | tpm_sha256_name_t name; /* sha256 of tpm_rsa2048_pubarea_t */ |
77 | | tpm_sha256_name_t qual_name; /* full tpm path of attested key */ |
78 | | }) |
79 | | |
80 | | /* Part 2, 11.2.4.5: TPM2B_PUBLIC_KEY_RSA */ |
81 | | PACKED_TYPE(tpm_rsa2048_key_t, |
82 | | struct tpm_rsa2048_key { |
83 | | uint16_t size; /* sizeof(body) */ |
84 | | uint8_t body[256]; |
85 | | }) |
86 | | |
87 | | /* Part 2, 12.2.3.5: TPMS_RSA_PARMS */ |
88 | | PACKED_TYPE(tpm_rsa2048_param_t, |
89 | | struct tpm_rsa2048_param { |
90 | | uint16_t symmetric; /* TPM_ALG_NULL */ |
91 | | uint16_t scheme; /* TPM_ALG_NULL */ |
92 | | uint16_t keybits; /* 2048 */ |
93 | | uint32_t exponent; /* zero (meaning 2^16 + 1) */ |
94 | | }) |
95 | | |
96 | | /* Part 2, 12.2.4: TPMT_PUBLIC */ |
97 | | PACKED_TYPE(tpm_rsa2048_pubarea_t, |
98 | | struct tpm_rsa2048_pubarea { |
99 | | uint16_t alg; /* TPM_ALG_RSA */ |
100 | | uint16_t hash; /* TPM_ALG_SHA256 */ |
101 | | uint32_t attr; |
102 | | tpm_sha256_digest_t policy; /* must be present? */ |
103 | | tpm_rsa2048_param_t param; |
104 | | tpm_rsa2048_key_t key; |
105 | | }) |
106 | | |
107 | | static int |
108 | | get_signed_sha1(tpm_sha1_data_t *dgst, const fido_blob_t *authdata, |
109 | | const fido_blob_t *clientdata) |
110 | 27 | { |
111 | 27 | const EVP_MD *md = NULL; |
112 | 27 | EVP_MD_CTX *ctx = NULL; |
113 | 27 | int ok = -1; |
114 | | |
115 | 27 | if ((dgst->size = sizeof(dgst->body)) != SHA_DIGEST_LENGTH || |
116 | 27 | (md = EVP_sha1()) == NULL || |
117 | 27 | (ctx = EVP_MD_CTX_new()) == NULL || |
118 | 27 | EVP_DigestInit_ex(ctx, md, NULL) != 1 || |
119 | 27 | EVP_DigestUpdate(ctx, authdata->ptr, authdata->len) != 1 || |
120 | 27 | EVP_DigestUpdate(ctx, clientdata->ptr, clientdata->len) != 1 || |
121 | 27 | EVP_DigestFinal_ex(ctx, dgst->body, NULL) != 1) { |
122 | 6 | fido_log_debug("%s: sha1", __func__); |
123 | 6 | goto fail; |
124 | 6 | } |
125 | | |
126 | 21 | ok = 0; |
127 | 27 | fail: |
128 | 27 | EVP_MD_CTX_free(ctx); |
129 | | |
130 | 27 | return (ok); |
131 | 21 | } |
132 | | |
133 | | static int |
134 | | get_signed_name(tpm_sha256_name_t *name, const fido_blob_t *pubarea) |
135 | 21 | { |
136 | 21 | name->alg = TPM_ALG_SHA256; |
137 | 21 | name->size = sizeof(name->alg) + sizeof(name->body); |
138 | 21 | if (sizeof(name->body) != SHA256_DIGEST_LENGTH || |
139 | 21 | SHA256(pubarea->ptr, pubarea->len, name->body) != name->body) { |
140 | 1 | fido_log_debug("%s: sha256", __func__); |
141 | 1 | return -1; |
142 | 1 | } |
143 | | |
144 | 20 | return 0; |
145 | 20 | } |
146 | | |
147 | | static void |
148 | | bswap_rsa2048_pubarea(tpm_rsa2048_pubarea_t *x) |
149 | 28 | { |
150 | 28 | x->alg = htobe16(x->alg); |
151 | 28 | x->hash = htobe16(x->hash); |
152 | 28 | x->attr = htobe32(x->attr); |
153 | 28 | x->policy.size = htobe16(x->policy.size); |
154 | 28 | x->param.symmetric = htobe16(x->param.symmetric); |
155 | 28 | x->param.scheme = htobe16(x->param.scheme); |
156 | 28 | x->param.keybits = htobe16(x->param.keybits); |
157 | 28 | x->key.size = htobe16(x->key.size); |
158 | 28 | } |
159 | | |
160 | | static void |
161 | | bswap_sha1_certinfo(tpm_sha1_attest_t *x) |
162 | 19 | { |
163 | 19 | x->magic = htobe32(x->magic); |
164 | 19 | x->type = htobe16(x->type); |
165 | 19 | x->signer.size = htobe16(x->signer.size); |
166 | 19 | x->data.size = htobe16(x->data.size); |
167 | 19 | x->name.alg = htobe16(x->name.alg); |
168 | 19 | x->name.size = htobe16(x->name.size); |
169 | 19 | } |
170 | | |
171 | | static int |
172 | | check_rsa2048_pubarea(const fido_blob_t *buf, const rs256_pk_t *pk) |
173 | 29 | { |
174 | 29 | const tpm_rsa2048_pubarea_t *actual; |
175 | 29 | tpm_rsa2048_pubarea_t expected; |
176 | 29 | int ok; |
177 | | |
178 | 29 | if (buf->len != sizeof(*actual)) { |
179 | 1 | fido_log_debug("%s: buf->len=%zu", __func__, buf->len); |
180 | 1 | return -1; |
181 | 1 | } |
182 | 28 | actual = (const void *)buf->ptr; |
183 | | |
184 | 28 | memset(&expected, 0, sizeof(expected)); |
185 | 28 | expected.alg = TPM_ALG_RSA; |
186 | 28 | expected.hash = TPM_ALG_SHA256; |
187 | 28 | expected.attr = be32toh(actual->attr); |
188 | 28 | expected.attr &= ~(TPMA_RESERVED|TPMA_CLEAR); |
189 | 28 | expected.attr |= (TPMA_FIXED|TPMA_FIXED_P|TPMA_SENSITIVE|TPMA_SIGN); |
190 | 28 | expected.policy = actual->policy; |
191 | 28 | expected.policy.size = sizeof(expected.policy.body); |
192 | 28 | expected.param.symmetric = TPM_ALG_NULL; |
193 | 28 | expected.param.scheme = TPM_ALG_NULL; |
194 | 28 | expected.param.keybits = 2048; |
195 | 28 | expected.param.exponent = 0; /* meaning 2^16+1 */ |
196 | 28 | expected.key.size = sizeof(expected.key.body); |
197 | 28 | memcpy(&expected.key.body, &pk->n, sizeof(expected.key.body)); |
198 | 28 | bswap_rsa2048_pubarea(&expected); |
199 | | |
200 | 28 | ok = timingsafe_bcmp(&expected, actual, sizeof(expected)); |
201 | 28 | explicit_bzero(&expected, sizeof(expected)); |
202 | | |
203 | 28 | return ok != 0 ? -1 : 0; |
204 | 28 | } |
205 | | |
206 | | static int |
207 | | check_sha1_certinfo(const fido_blob_t *buf, const fido_blob_t *clientdata_hash, |
208 | | const fido_blob_t *authdata_raw, const fido_blob_t *pubarea) |
209 | 27 | { |
210 | 27 | const tpm_sha1_attest_t *actual; |
211 | 27 | tpm_sha1_attest_t expected; |
212 | 27 | tpm_sha1_data_t signed_data; |
213 | 27 | tpm_sha256_name_t signed_name; |
214 | 27 | int ok = -1; |
215 | | |
216 | 27 | memset(&signed_data, 0, sizeof(signed_data)); |
217 | 27 | memset(&signed_name, 0, sizeof(signed_name)); |
218 | | |
219 | 27 | if (get_signed_sha1(&signed_data, authdata_raw, clientdata_hash) < 0 || |
220 | 27 | get_signed_name(&signed_name, pubarea) < 0) { |
221 | 7 | fido_log_debug("%s: get_signed_sha1/name", __func__); |
222 | 7 | goto fail; |
223 | 7 | } |
224 | 20 | if (buf->len != sizeof(*actual)) { |
225 | 1 | fido_log_debug("%s: buf->len=%zu", __func__, buf->len); |
226 | 1 | goto fail; |
227 | 1 | } |
228 | 19 | actual = (const void *)buf->ptr; |
229 | | |
230 | 19 | memset(&expected, 0, sizeof(expected)); |
231 | 19 | expected.magic = TPM_MAGIC; |
232 | 19 | expected.type = TPM_ST_CERTIFY; |
233 | 19 | expected.signer = actual->signer; |
234 | 19 | expected.signer.size = sizeof(expected.signer.alg) + |
235 | 19 | sizeof(expected.signer.body); |
236 | 19 | expected.data = signed_data; |
237 | 19 | expected.clock = actual->clock; |
238 | 19 | expected.clock.safe = 1; |
239 | 19 | expected.fwversion = actual->fwversion; |
240 | 19 | expected.name = signed_name; |
241 | 19 | expected.qual_name = actual->qual_name; |
242 | 19 | bswap_sha1_certinfo(&expected); |
243 | | |
244 | 19 | ok = timingsafe_bcmp(&expected, actual, sizeof(expected)); |
245 | 27 | fail: |
246 | 27 | explicit_bzero(&expected, sizeof(expected)); |
247 | 27 | explicit_bzero(&signed_data, sizeof(signed_data)); |
248 | 27 | explicit_bzero(&signed_name, sizeof(signed_name)); |
249 | | |
250 | 27 | return ok != 0 ? -1 : 0; |
251 | 19 | } |
252 | | |
253 | | int |
254 | | fido_get_signed_hash_tpm(fido_blob_t *dgst, const fido_blob_t *clientdata_hash, |
255 | | const fido_blob_t *authdata_raw, const fido_attstmt_t *attstmt, |
256 | | const fido_attcred_t *attcred) |
257 | 30 | { |
258 | 30 | const fido_blob_t *pubarea = &attstmt->pubarea; |
259 | 30 | const fido_blob_t *certinfo = &attstmt->certinfo; |
260 | | |
261 | 30 | if (attstmt->alg != COSE_RS1 || attcred->type != COSE_RS256) { |
262 | 1 | fido_log_debug("%s: unsupported alg %d, type %d", __func__, |
263 | 1 | attstmt->alg, attcred->type); |
264 | 1 | return -1; |
265 | 1 | } |
266 | | |
267 | 29 | if (check_rsa2048_pubarea(pubarea, &attcred->pubkey.rs256) < 0) { |
268 | 2 | fido_log_debug("%s: check_rsa2048_pubarea", __func__); |
269 | 2 | return -1; |
270 | 2 | } |
271 | | |
272 | 27 | if (check_sha1_certinfo(certinfo, clientdata_hash, authdata_raw, |
273 | 27 | pubarea) < 0) { |
274 | 15 | fido_log_debug("%s: check_sha1_certinfo", __func__); |
275 | 15 | return -1; |
276 | 15 | } |
277 | | |
278 | 12 | if (dgst->len < SHA_DIGEST_LENGTH || |
279 | 12 | SHA1(certinfo->ptr, certinfo->len, dgst->ptr) != dgst->ptr) { |
280 | 1 | fido_log_debug("%s: sha1", __func__); |
281 | 1 | return -1; |
282 | 1 | } |
283 | 11 | dgst->len = SHA_DIGEST_LENGTH; |
284 | | |
285 | 11 | return 0; |
286 | 11 | } |