/*
* Copyright 2014 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "asymmetric_key.h"
#include <new>
#include <openssl/asn1.h>
#include <openssl/stack.h>
#include <openssl/x509.h>
#include <openssl/x509v3.h>
#include "attestation_record.h"
#include "openssl_err.h"
#include "openssl_utils.h"
namespace keymaster {
namespace {
constexpr int kDigitalSignatureKeyUsageBit = 0;
constexpr int kKeyEnciphermentKeyUsageBit = 2;
constexpr int kDataEnciphermentKeyUsageBit = 3;
constexpr int kMaxKeyUsageBit = 8;
template <typename T> T min(T a, T b) {
return (a < b) ? a : b;
}
static keymaster_error_t add_key_usage_extension(const AuthorizationSet& tee_enforced,
const AuthorizationSet& sw_enforced,
X509* certificate) {
// Build BIT_STRING with correct contents.
ASN1_BIT_STRING_Ptr key_usage(ASN1_BIT_STRING_new());
for (size_t i = 0; i <= kMaxKeyUsageBit; ++i) {
if (!ASN1_BIT_STRING_set_bit(key_usage.get(), i, 0)) {
return TranslateLastOpenSslError();
}
}
if (tee_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_SIGN) ||
tee_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_VERIFY) ||
sw_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_SIGN) ||
sw_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_VERIFY)) {
if (!ASN1_BIT_STRING_set_bit(key_usage.get(), kDigitalSignatureKeyUsageBit, 1)) {
return TranslateLastOpenSslError();
}
}
if (tee_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_ENCRYPT) ||
tee_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_DECRYPT) ||
sw_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_ENCRYPT) ||
sw_enforced.Contains(TAG_PURPOSE, KM_PURPOSE_DECRYPT)) {
if (!ASN1_BIT_STRING_set_bit(key_usage.get(), kKeyEnciphermentKeyUsageBit, 1) ||
!ASN1_BIT_STRING_set_bit(key_usage.get(), kDataEnciphermentKeyUsageBit, 1)) {
return TranslateLastOpenSslError();
}
}
// Convert to octets
int len = i2d_ASN1_BIT_STRING(key_usage.get(), nullptr);
if (len < 0) {
return TranslateLastOpenSslError();
}
UniquePtr<uint8_t[]> asn1_key_usage(new uint8_t[len]);
if (!asn1_key_usage.get()) {
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
}
uint8_t* p = asn1_key_usage.get();
len = i2d_ASN1_BIT_STRING(key_usage.get(), &p);
if (len < 0) {
return TranslateLastOpenSslError();
}
// Build OCTET_STRING
ASN1_OCTET_STRING_Ptr key_usage_str(ASN1_OCTET_STRING_new());
if (!key_usage_str.get() ||
!ASN1_OCTET_STRING_set(key_usage_str.get(), asn1_key_usage.get(), len)) {
return TranslateLastOpenSslError();
}
X509_EXTENSION_Ptr key_usage_extension(X509_EXTENSION_create_by_NID(nullptr, //
NID_key_usage, //
false /* critical */,
key_usage_str.get()));
if (!key_usage_extension.get()) {
return TranslateLastOpenSslError();
}
if (!X509_add_ext(certificate, key_usage_extension.get() /* Don't release; copied */,
-1 /* insert at end */)) {
return TranslateLastOpenSslError();
}
return KM_ERROR_OK;
}
} // anonymous namespace
keymaster_error_t AsymmetricKey::formatted_key_material(keymaster_key_format_t format,
UniquePtr<uint8_t[]>* material,
size_t* size) const {
if (format != KM_KEY_FORMAT_X509)
return KM_ERROR_UNSUPPORTED_KEY_FORMAT;
if (material == NULL || size == NULL)
return KM_ERROR_OUTPUT_PARAMETER_NULL;
EVP_PKEY_Ptr pkey(EVP_PKEY_new());
if (!InternalToEvp(pkey.get()))
return TranslateLastOpenSslError();
int key_data_length = i2d_PUBKEY(pkey.get(), NULL);
if (key_data_length <= 0)
return TranslateLastOpenSslError();
material->reset(new (std::nothrow) uint8_t[key_data_length]);
if (material->get() == NULL)
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
uint8_t* tmp = material->get();
if (i2d_PUBKEY(pkey.get(), &tmp) != key_data_length) {
material->reset();
return TranslateLastOpenSslError();
}
*size = key_data_length;
return KM_ERROR_OK;
}
static keymaster_error_t build_attestation_extension(const AuthorizationSet& attest_params,
const AuthorizationSet& tee_enforced,
const AuthorizationSet& sw_enforced,
const KeymasterContext& context,
X509_EXTENSION_Ptr* extension) {
ASN1_OBJECT_Ptr oid(
OBJ_txt2obj(kAttestionRecordOid, 1 /* accept numerical dotted string form only */));
if (!oid.get())
return TranslateLastOpenSslError();
UniquePtr<uint8_t[]> attest_bytes;
size_t attest_bytes_len;
keymaster_error_t error = build_attestation_record(attest_params, sw_enforced, tee_enforced,
context, &attest_bytes, &attest_bytes_len);
if (error != KM_ERROR_OK)
return error;
ASN1_OCTET_STRING_Ptr attest_str(ASN1_OCTET_STRING_new());
if (!attest_str.get() ||
!ASN1_OCTET_STRING_set(attest_str.get(), attest_bytes.get(), attest_bytes_len))
return TranslateLastOpenSslError();
extension->reset(
X509_EXTENSION_create_by_OBJ(nullptr, oid.get(), 0 /* not critical */, attest_str.get()));
if (!extension->get())
return TranslateLastOpenSslError();
return KM_ERROR_OK;
}
static bool add_public_key(EVP_PKEY* key, X509* certificate, keymaster_error_t* error) {
if (!X509_set_pubkey(certificate, key)) {
*error = TranslateLastOpenSslError();
return false;
}
return true;
}
static bool add_attestation_extension(const AuthorizationSet& attest_params,
const AuthorizationSet& tee_enforced,
const AuthorizationSet& sw_enforced,
const KeymasterContext& context, X509* certificate,
keymaster_error_t* error) {
X509_EXTENSION_Ptr attest_extension;
*error = build_attestation_extension(attest_params, tee_enforced, sw_enforced, context,
&attest_extension);
if (*error != KM_ERROR_OK)
return false;
if (!X509_add_ext(certificate, attest_extension.get() /* Don't release; copied */,
-1 /* insert at end */)) {
*error = TranslateLastOpenSslError();
return false;
}
return true;
}
static keymaster_error_t get_certificate_blob(X509* certificate, keymaster_blob_t* blob) {
int len = i2d_X509(certificate, nullptr);
if (len < 0)
return TranslateLastOpenSslError();
uint8_t* data = new uint8_t[len];
if (!data)
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
uint8_t* p = data;
i2d_X509(certificate, &p);
blob->data_length = len;
blob->data = data;
return KM_ERROR_OK;
}
static bool allocate_cert_chain(size_t entry_count, keymaster_cert_chain_t* chain,
keymaster_error_t* error) {
if (chain->entries) {
for (size_t i = 0; i < chain->entry_count; ++i)
delete[] chain->entries[i].data;
delete[] chain->entries;
}
chain->entry_count = entry_count;
chain->entries = new keymaster_blob_t[entry_count];
if (!chain->entries) {
*error = KM_ERROR_MEMORY_ALLOCATION_FAILED;
return false;
}
return true;
}
// Copies the intermediate and root certificates into chain, leaving the first slot for the leaf
// certificate.
static bool copy_attestation_chain(const KeymasterContext& context,
keymaster_algorithm_t sign_algorithm,
keymaster_cert_chain_t* chain, keymaster_error_t* error) {
UniquePtr<keymaster_cert_chain_t, CertificateChainDelete> attest_key_chain(
context.AttestationChain(sign_algorithm, error));
if (!attest_key_chain.get())
return false;
if (!allocate_cert_chain(attest_key_chain->entry_count + 1, chain, error))
return false;
chain->entries[0].data = nullptr; // Leave empty for the leaf certificate.
chain->entries[1].data_length = 0;
for (size_t i = 0; i < attest_key_chain->entry_count; ++i) {
chain->entries[i + 1] = attest_key_chain->entries[i];
attest_key_chain->entries[i].data = nullptr;
}
return true;
}
keymaster_error_t AsymmetricKey::GenerateAttestation(const KeymasterContext& context,
const AuthorizationSet& attest_params,
const AuthorizationSet& tee_enforced,
const AuthorizationSet& sw_enforced,
keymaster_cert_chain_t* cert_chain) const {
keymaster_algorithm_t sign_algorithm;
if ((!sw_enforced.GetTagValue(TAG_ALGORITHM, &sign_algorithm) &&
!tee_enforced.GetTagValue(TAG_ALGORITHM, &sign_algorithm)))
return KM_ERROR_UNKNOWN_ERROR;
if ((sign_algorithm != KM_ALGORITHM_RSA && sign_algorithm != KM_ALGORITHM_EC))
return KM_ERROR_INCOMPATIBLE_ALGORITHM;
EVP_PKEY_Ptr pkey(EVP_PKEY_new());
if (!InternalToEvp(pkey.get()))
return TranslateLastOpenSslError();
X509_Ptr certificate(X509_new());
if (!certificate.get())
return TranslateLastOpenSslError();
if (!X509_set_version(certificate.get(), 2 /* version 3, but zero-based */))
return TranslateLastOpenSslError();
ASN1_INTEGER_Ptr serialNumber(ASN1_INTEGER_new());
if (!serialNumber.get() || !ASN1_INTEGER_set(serialNumber.get(), 1) ||
!X509_set_serialNumber(certificate.get(), serialNumber.get() /* Don't release; copied */))
return TranslateLastOpenSslError();
X509_NAME_Ptr subjectName(X509_NAME_new());
if (!subjectName.get() ||
!X509_NAME_add_entry_by_txt(subjectName.get(), "CN", MBSTRING_ASC,
reinterpret_cast<const uint8_t*>("Android Keystore Key"),
-1 /* len */, -1 /* loc */, 0 /* set */) ||
!X509_set_subject_name(certificate.get(), subjectName.get() /* Don't release; copied */))
return TranslateLastOpenSslError();
ASN1_TIME_Ptr notBefore(ASN1_TIME_new());
uint64_t activeDateTime = 0;
authorizations().GetTagValue(TAG_ACTIVE_DATETIME, &activeDateTime);
if (!notBefore.get() || !ASN1_TIME_set(notBefore.get(), activeDateTime / 1000) ||
!X509_set_notBefore(certificate.get(), notBefore.get() /* Don't release; copied */))
return TranslateLastOpenSslError();
ASN1_TIME_Ptr notAfter(ASN1_TIME_new());
uint64_t usageExpireDateTime = UINT64_MAX;
authorizations().GetTagValue(TAG_USAGE_EXPIRE_DATETIME, &usageExpireDateTime);
// TODO(swillden): When trusty can use the C++ standard library change the calculation of
// notAfterTime to use std::numeric_limits<time_t>::max(), rather than assuming that time_t is
// 32 bits.
time_t notAfterTime = min(static_cast<uint64_t>(UINT32_MAX), usageExpireDateTime / 1000);
if (!notAfter.get() || !ASN1_TIME_set(notAfter.get(), notAfterTime) ||
!X509_set_notAfter(certificate.get(), notAfter.get() /* Don't release; copied */))
return TranslateLastOpenSslError();
keymaster_error_t error = add_key_usage_extension(tee_enforced, sw_enforced, certificate.get());
if (error != KM_ERROR_OK) {
return error;
}
EVP_PKEY_Ptr sign_key(context.AttestationKey(sign_algorithm, &error));
if (!sign_key.get() || //
!add_public_key(pkey.get(), certificate.get(), &error) ||
!add_attestation_extension(attest_params, tee_enforced, sw_enforced, context,
certificate.get(), &error))
return error;
if (!copy_attestation_chain(context, sign_algorithm, cert_chain, &error))
return error;
// Copy subject key identifier from cert_chain->entries[1] as authority key_id.
if (cert_chain->entry_count < 2) {
// cert_chain must have at least two entries, one for the cert we're trying to create and
// one for the cert for the key that signs the new cert.
return KM_ERROR_UNKNOWN_ERROR;
}
const uint8_t* p = cert_chain->entries[1].data;
X509_Ptr signing_cert(d2i_X509(nullptr, &p, cert_chain->entries[1].data_length));
if (!signing_cert.get()) {
return TranslateLastOpenSslError();
}
// Set issuer to subject of batch certificate.
X509_NAME* issuerSubject = X509_get_subject_name(signing_cert.get());
if (!issuerSubject) {
return KM_ERROR_UNKNOWN_ERROR;
}
if (!X509_set_issuer_name(certificate.get(), issuerSubject)) {
return TranslateLastOpenSslError();
}
UniquePtr<X509V3_CTX> x509v3_ctx(new X509V3_CTX);
*x509v3_ctx = {};
X509V3_set_ctx(x509v3_ctx.get(), signing_cert.get(), certificate.get(), nullptr /* req */,
nullptr /* crl */, 0 /* flags */);
X509_EXTENSION_Ptr auth_key_id(X509V3_EXT_nconf_nid(nullptr /* conf */, x509v3_ctx.get(),
NID_authority_key_identifier,
const_cast<char*>("keyid:always")));
if (!auth_key_id.get() ||
!X509_add_ext(certificate.get(), auth_key_id.get() /* Don't release; copied */,
-1 /* insert at end */)) {
return TranslateLastOpenSslError();
}
if (!X509_sign(certificate.get(), sign_key.get(), EVP_sha256()))
return TranslateLastOpenSslError();
return get_certificate_blob(certificate.get(), &cert_chain->entries[0]);
}
} // namespace keymaster