1 /*
2 * Copyright 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "asymmetric_key.h"
18
19 #include <new>
20
21 #include <openssl/asn1.h>
22 #include <openssl/stack.h>
23 #include <openssl/x509.h>
24 #include <openssl/x509v3.h>
25
26 #include "attestation_record.h"
27 #include "openssl_err.h"
28 #include "openssl_utils.h"
29
30 namespace keymaster {
31
32 namespace {
33
34 constexpr int kDigitalSignatureKeyUsageBit = 0;
35 constexpr int kKeyEnciphermentKeyUsageBit = 2;
36 constexpr int kDataEnciphermentKeyUsageBit = 3;
37 constexpr int kMaxKeyUsageBit = 8;
38
min(T a,T b)39 template <typename T> T min(T a, T b) {
40 return (a < b) ? a : b;
41 }
42
add_key_usage_extension(const AuthorizationSet & tee_enforced,const AuthorizationSet & sw_enforced,X509 * certificate)43 static keymaster_error_t add_key_usage_extension(const AuthorizationSet& tee_enforced,
44 const AuthorizationSet& sw_enforced,
45 X509* certificate) {
46 // Build BIT_STRING with correct contents.
47 ASN1_BIT_STRING_Ptr key_usage(ASN1_BIT_STRING_new());
48
49 for (size_t i = 0; i <= kMaxKeyUsageBit; ++i) {
50 if (!ASN1_BIT_STRING_set_bit(key_usage.get(), i, 0)) {
51 return TranslateLastOpenSslError();
52 }
53 }
54
55 if (tee_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_SIGN) ||
56 tee_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_VERIFY) ||
57 sw_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_SIGN) ||
58 sw_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_VERIFY)) {
59 if (!ASN1_BIT_STRING_set_bit(key_usage.get(), kDigitalSignatureKeyUsageBit, 1)) {
60 return TranslateLastOpenSslError();
61 }
62 }
63
64 if (tee_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_ENCRYPT) ||
65 tee_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_DECRYPT) ||
66 sw_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_ENCRYPT) ||
67 sw_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_DECRYPT)) {
68 if (!ASN1_BIT_STRING_set_bit(key_usage.get(), kKeyEnciphermentKeyUsageBit, 1) ||
69 !ASN1_BIT_STRING_set_bit(key_usage.get(), kDataEnciphermentKeyUsageBit, 1)) {
70 return TranslateLastOpenSslError();
71 }
72 }
73
74 // Convert to octets
75 int len = i2d_ASN1_BIT_STRING(key_usage.get(), nullptr);
76 if (len < 0) {
77 return TranslateLastOpenSslError();
78 }
79 UniquePtr<uint8_t[]> asn1_key_usage(new uint8_t[len]);
80 if (!asn1_key_usage.get()) {
81 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
82 }
83 uint8_t* p = asn1_key_usage.get();
84 len = i2d_ASN1_BIT_STRING(key_usage.get(), &p);
85 if (len < 0) {
86 return TranslateLastOpenSslError();
87 }
88
89 // Build OCTET_STRING
90 ASN1_OCTET_STRING_Ptr key_usage_str(ASN1_OCTET_STRING_new());
91 if (!key_usage_str.get() ||
92 !ASN1_OCTET_STRING_set(key_usage_str.get(), asn1_key_usage.get(), len)) {
93 return TranslateLastOpenSslError();
94 }
95
96 X509_EXTENSION_Ptr key_usage_extension(X509_EXTENSION_create_by_NID(nullptr, //
97 NID_key_usage, //
98 false /* critical */,
99 key_usage_str.get()));
100 if (!key_usage_extension.get()) {
101 return TranslateLastOpenSslError();
102 }
103
104 if (!X509_add_ext(certificate, key_usage_extension.get() /* Don't release; copied */,
105 -1 /* insert at end */)) {
106 return TranslateLastOpenSslError();
107 }
108
109 return KM_ERROR_OK;
110 }
111
112 } // anonymous namespace
113
formatted_key_material(keymaster_key_format_t format,UniquePtr<uint8_t[]> * material,size_t * size) const114 keymaster_error_t AsymmetricKey::formatted_key_material(keymaster_key_format_t format,
115 UniquePtr<uint8_t[]>* material,
116 size_t* size) const {
117 if (format != KM_KEY_FORMAT_X509)
118 return KM_ERROR_UNSUPPORTED_KEY_FORMAT;
119
120 if (material == NULL || size == NULL)
121 return KM_ERROR_OUTPUT_PARAMETER_NULL;
122
123 EVP_PKEY_Ptr pkey(EVP_PKEY_new());
124 if (!InternalToEvp(pkey.get()))
125 return TranslateLastOpenSslError();
126
127 int key_data_length = i2d_PUBKEY(pkey.get(), NULL);
128 if (key_data_length <= 0)
129 return TranslateLastOpenSslError();
130
131 material->reset(new (std::nothrow) uint8_t[key_data_length]);
132 if (material->get() == NULL)
133 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
134
135 uint8_t* tmp = material->get();
136 if (i2d_PUBKEY(pkey.get(), &tmp) != key_data_length) {
137 material->reset();
138 return TranslateLastOpenSslError();
139 }
140
141 *size = key_data_length;
142 return KM_ERROR_OK;
143 }
144
build_attestation_extension(const AuthorizationSet & attest_params,const AuthorizationSet & tee_enforced,const AuthorizationSet & sw_enforced,const KeymasterContext & context,X509_EXTENSION_Ptr * extension)145 static keymaster_error_t build_attestation_extension(const AuthorizationSet& attest_params,
146 const AuthorizationSet& tee_enforced,
147 const AuthorizationSet& sw_enforced,
148 const KeymasterContext& context,
149 X509_EXTENSION_Ptr* extension) {
150 ASN1_OBJECT_Ptr oid(
151 OBJ_txt2obj(kAttestionRecordOid, 1 /* accept numerical dotted string form only */));
152 if (!oid.get())
153 return TranslateLastOpenSslError();
154
155 UniquePtr<uint8_t[]> attest_bytes;
156 size_t attest_bytes_len;
157 keymaster_error_t error = build_attestation_record(attest_params, sw_enforced, tee_enforced,
158 context, &attest_bytes, &attest_bytes_len);
159 if (error != KM_ERROR_OK)
160 return error;
161
162 ASN1_OCTET_STRING_Ptr attest_str(ASN1_OCTET_STRING_new());
163 if (!attest_str.get() ||
164 !ASN1_OCTET_STRING_set(attest_str.get(), attest_bytes.get(), attest_bytes_len))
165 return TranslateLastOpenSslError();
166
167 extension->reset(
168 X509_EXTENSION_create_by_OBJ(nullptr, oid.get(), 0 /* not critical */, attest_str.get()));
169 if (!extension->get())
170 return TranslateLastOpenSslError();
171
172 return KM_ERROR_OK;
173 }
174
add_public_key(EVP_PKEY * key,X509 * certificate,keymaster_error_t * error)175 static bool add_public_key(EVP_PKEY* key, X509* certificate, keymaster_error_t* error) {
176 if (!X509_set_pubkey(certificate, key)) {
177 *error = TranslateLastOpenSslError();
178 return false;
179 }
180 return true;
181 }
182
add_attestation_extension(const AuthorizationSet & attest_params,const AuthorizationSet & tee_enforced,const AuthorizationSet & sw_enforced,const KeymasterContext & context,X509 * certificate,keymaster_error_t * error)183 static bool add_attestation_extension(const AuthorizationSet& attest_params,
184 const AuthorizationSet& tee_enforced,
185 const AuthorizationSet& sw_enforced,
186 const KeymasterContext& context, X509* certificate,
187 keymaster_error_t* error) {
188 X509_EXTENSION_Ptr attest_extension;
189 *error = build_attestation_extension(attest_params, tee_enforced, sw_enforced, context,
190 &attest_extension);
191 if (*error != KM_ERROR_OK)
192 return false;
193
194 if (!X509_add_ext(certificate, attest_extension.get() /* Don't release; copied */,
195 -1 /* insert at end */)) {
196 *error = TranslateLastOpenSslError();
197 return false;
198 }
199
200 return true;
201 }
202
get_certificate_blob(X509 * certificate,keymaster_blob_t * blob)203 static keymaster_error_t get_certificate_blob(X509* certificate, keymaster_blob_t* blob) {
204 int len = i2d_X509(certificate, nullptr);
205 if (len < 0)
206 return TranslateLastOpenSslError();
207
208 uint8_t* data = new uint8_t[len];
209 if (!data)
210 return KM_ERROR_MEMORY_ALLOCATION_FAILED;
211
212 uint8_t* p = data;
213 i2d_X509(certificate, &p);
214
215 blob->data_length = len;
216 blob->data = data;
217
218 return KM_ERROR_OK;
219 }
220
allocate_cert_chain(size_t entry_count,keymaster_cert_chain_t * chain,keymaster_error_t * error)221 static bool allocate_cert_chain(size_t entry_count, keymaster_cert_chain_t* chain,
222 keymaster_error_t* error) {
223 if (chain->entries) {
224 for (size_t i = 0; i < chain->entry_count; ++i)
225 delete[] chain->entries[i].data;
226 delete[] chain->entries;
227 }
228
229 chain->entry_count = entry_count;
230 chain->entries = new keymaster_blob_t[entry_count];
231 if (!chain->entries) {
232 *error = KM_ERROR_MEMORY_ALLOCATION_FAILED;
233 return false;
234 }
235 return true;
236 }
237
238 // Copies the intermediate and root certificates into chain, leaving the first slot for the leaf
239 // certificate.
copy_attestation_chain(const KeymasterContext & context,keymaster_algorithm_t sign_algorithm,keymaster_cert_chain_t * chain,keymaster_error_t * error)240 static bool copy_attestation_chain(const KeymasterContext& context,
241 keymaster_algorithm_t sign_algorithm,
242 keymaster_cert_chain_t* chain, keymaster_error_t* error) {
243
244 UniquePtr<keymaster_cert_chain_t, CertificateChainDelete> attest_key_chain(
245 context.AttestationChain(sign_algorithm, error));
246 if (!attest_key_chain.get())
247 return false;
248
249 if (!allocate_cert_chain(attest_key_chain->entry_count + 1, chain, error))
250 return false;
251
252 chain->entries[0].data = nullptr; // Leave empty for the leaf certificate.
253 chain->entries[1].data_length = 0;
254
255 for (size_t i = 0; i < attest_key_chain->entry_count; ++i) {
256 chain->entries[i + 1] = attest_key_chain->entries[i];
257 attest_key_chain->entries[i].data = nullptr;
258 }
259
260 return true;
261 }
262
GenerateAttestation(const KeymasterContext & context,const AuthorizationSet & attest_params,const AuthorizationSet & tee_enforced,const AuthorizationSet & sw_enforced,keymaster_cert_chain_t * cert_chain) const263 keymaster_error_t AsymmetricKey::GenerateAttestation(const KeymasterContext& context,
264 const AuthorizationSet& attest_params,
265 const AuthorizationSet& tee_enforced,
266 const AuthorizationSet& sw_enforced,
267 keymaster_cert_chain_t* cert_chain) const {
268
269 keymaster_algorithm_t sign_algorithm;
270 if ((!sw_enforced.GetTagValue(TAG_ALGORITHM, &sign_algorithm) &&
271 !tee_enforced.GetTagValue(TAG_ALGORITHM, &sign_algorithm)))
272 return KM_ERROR_UNKNOWN_ERROR;
273
274 if ((sign_algorithm != KM_ALGORITHM_RSA && sign_algorithm != KM_ALGORITHM_EC))
275 return KM_ERROR_INCOMPATIBLE_ALGORITHM;
276
277 EVP_PKEY_Ptr pkey(EVP_PKEY_new());
278 if (!InternalToEvp(pkey.get()))
279 return TranslateLastOpenSslError();
280
281 X509_Ptr certificate(X509_new());
282 if (!certificate.get())
283 return TranslateLastOpenSslError();
284
285 if (!X509_set_version(certificate.get(), 2 /* version 3, but zero-based */))
286 return TranslateLastOpenSslError();
287
288 ASN1_INTEGER_Ptr serialNumber(ASN1_INTEGER_new());
289 if (!serialNumber.get() || !ASN1_INTEGER_set(serialNumber.get(), 1) ||
290 !X509_set_serialNumber(certificate.get(), serialNumber.get() /* Don't release; copied */))
291 return TranslateLastOpenSslError();
292
293 // TODO(swillden): Find useful values (if possible) for issuerName and subjectName.
294 X509_NAME_Ptr issuerName(X509_NAME_new());
295 if (!issuerName.get() ||
296 !X509_NAME_add_entry_by_txt(issuerName.get(), "CN", MBSTRING_ASC,
297 reinterpret_cast<const uint8_t*>("Android Keymaster"),
298 -1 /* len */, -1 /* loc */, 0 /* set */) ||
299 !X509_set_issuer_name(certificate.get(), issuerName.get() /* Don't release; copied */))
300 return TranslateLastOpenSslError();
301
302 X509_NAME_Ptr subjectName(X509_NAME_new());
303 if (!subjectName.get() ||
304 !X509_NAME_add_entry_by_txt(subjectName.get(), "CN", MBSTRING_ASC,
305 reinterpret_cast<const uint8_t*>("A Keymaster Key"),
306 -1 /* len */, -1 /* loc */, 0 /* set */) ||
307 !X509_set_subject_name(certificate.get(), subjectName.get() /* Don't release; copied */))
308 return TranslateLastOpenSslError();
309
310 ASN1_TIME_Ptr notBefore(ASN1_TIME_new());
311 uint64_t activeDateTime = 0;
312 authorizations().GetTagValue(TAG_ACTIVE_DATETIME, &activeDateTime);
313 if (!notBefore.get() || !ASN1_TIME_set(notBefore.get(), activeDateTime / 1000) ||
314 !X509_set_notBefore(certificate.get(), notBefore.get() /* Don't release; copied */))
315 return TranslateLastOpenSslError();
316
317 ASN1_TIME_Ptr notAfter(ASN1_TIME_new());
318 uint64_t usageExpireDateTime = UINT64_MAX;
319 authorizations().GetTagValue(TAG_USAGE_EXPIRE_DATETIME, &usageExpireDateTime);
320 // TODO(swillden): When trusty can use the C++ standard library change the calculation of
321 // notAfterTime to use std::numeric_limits<time_t>::max(), rather than assuming that time_t is
322 // 32 bits.
323 time_t notAfterTime = min(static_cast<uint64_t>(UINT32_MAX), usageExpireDateTime / 1000);
324 if (!notAfter.get() || !ASN1_TIME_set(notAfter.get(), notAfterTime) ||
325 !X509_set_notAfter(certificate.get(), notAfter.get() /* Don't release; copied */))
326 return TranslateLastOpenSslError();
327
328 keymaster_error_t error = add_key_usage_extension(tee_enforced, sw_enforced, certificate.get());
329 if (error != KM_ERROR_OK) {
330 return error;
331 }
332
333 EVP_PKEY_Ptr sign_key(context.AttestationKey(sign_algorithm, &error));
334
335 if (!sign_key.get() || //
336 !add_public_key(pkey.get(), certificate.get(), &error) ||
337 !add_attestation_extension(attest_params, tee_enforced, sw_enforced, context,
338 certificate.get(), &error))
339 return error;
340
341 if (!copy_attestation_chain(context, sign_algorithm, cert_chain, &error))
342 return error;
343
344 // Copy subject key identifier from cert_chain->entries[1] as authority key_id.
345 if (cert_chain->entry_count < 2) {
346 // cert_chain must have at least two entries, one for the cert we're trying to create and
347 // one for the cert for the key that signs the new cert.
348 return KM_ERROR_UNKNOWN_ERROR;
349 }
350
351 const uint8_t* p = cert_chain->entries[1].data;
352 X509_Ptr signing_cert(d2i_X509(nullptr, &p, cert_chain->entries[1].data_length));
353 if (!signing_cert.get()) {
354 return TranslateLastOpenSslError();
355 }
356
357 UniquePtr<X509V3_CTX> x509v3_ctx(new X509V3_CTX);
358 *x509v3_ctx = {};
359 X509V3_set_ctx(x509v3_ctx.get(), signing_cert.get(), certificate.get(), nullptr /* req */,
360 nullptr /* crl */, 0 /* flags */);
361
362 X509_EXTENSION_Ptr auth_key_id(X509V3_EXT_nconf_nid(nullptr /* conf */, x509v3_ctx.get(),
363 NID_authority_key_identifier,
364 const_cast<char*>("keyid:always")));
365 if (!auth_key_id.get() ||
366 !X509_add_ext(certificate.get(), auth_key_id.get() /* Don't release; copied */,
367 -1 /* insert at end */)) {
368 return TranslateLastOpenSslError();
369 }
370
371 if (!X509_sign(certificate.get(), sign_key.get(), EVP_sha256()))
372 return TranslateLastOpenSslError();
373
374 return get_certificate_blob(certificate.get(), &cert_chain->entries[0]);
375 }
376
377 } // namespace keymaster
378