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KeyMint: Fix device-unique attestation chain specification

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Fix the device-unique attestation chain specification: The chain should
have two or three certificates.
In case of two certificates, the device-unique key should be used for
the self-signed root.
In case of three certificates, the device-unique key should be certified
by another key (ideally shared by all StrongBox instances from the same
manufacturer, to ease validation).

Adjust the device-unique attestation tests to accept two or three
certificates in the chain.

Additionally, the current StrongBox KeyMint implementation can not yet
generate fully-valid chains (with matching subjects and issuers), so
relax that check.

Bug: 191361618
Test: m VtsAidlKeyMintTargetTest
Change-Id: I6e6bca33ebb4af67cac8e41a39e9c305d0f1345f
This commit is contained in:
Eran Messeri
2021-07-06 12:07:57 +01:00
parent f4c8ff9bef
commit 03d7a1a4f3
4 changed files with 28 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

17
security/keymint/aidl/android/hardware/security/keymint/Tag.aidl
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@@ -827,11 +827,22 @@ enum Tag {
/**
* DEVICE_UNIQUE_ATTESTATION is an argument to IKeyMintDevice::attested key generation/import
* operations. It indicates that attestation using a device-unique key is requested, rather
* than a batch key. When a device-unique key is used, the returned chain should contain two
* certificates:
* than a batch key. When a device-unique key is used, the returned chain should contain two or
* three certificates.
*
* In case the chain contains two certificates, they should be:
* * The attestation certificate, containing the attestation extension, as described in
KeyCreationResult.aidl.
* KeyCreationResult.aidl.
* * A self-signed root certificate, signed by the device-unique key.
*
* In case the chain contains three certificates, they should be:
* * The attestation certificate, containing the attestation extension, as described in
* KeyCreationResult.aidl, signed by the device-unique key.
* * An intermediate certificate, containing the public portion of the device-unique key.
* * A self-signed root certificate, signed by a dedicated key, certifying the
* intermediate. Ideally, the dedicated key would be the same for all StrongBox
* instances of the same manufacturer to ease validation.
*
* No additional chained certificates are provided. Only SecurityLevel::STRONGBOX
* IKeyMintDevices may support device-unique attestations. SecurityLevel::TRUSTED_ENVIRONMENT
* IKeyMintDevices must return ErrorCode::INVALID_ARGUMENT if they receive

13
security/keymint/aidl/vts/functional/DeviceUniqueAttestationTest.cpp
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@@ -40,11 +40,16 @@ class DeviceUniqueAttestationTest : public KeyMintAidlTestBase {
AuthorizationSet crypto_params = SecLevelAuthorizations(key_characteristics);
// The device-unique attestation chain should contain exactly two certificates:
// The device-unique attestation chain should contain exactly three certificates:
// * The leaf with the attestation extension.
// * A self-signed root, signed using the device-unique key.
ASSERT_EQ(cert_chain_.size(), 2);
EXPECT_TRUE(ChainSignaturesAreValid(cert_chain_));
// * An intermediate, signing the leaf using the device-unique key.
// * A self-signed root, signed using some authority's key, certifying
// the device-unique key.
const size_t chain_length = cert_chain_.size();
ASSERT_TRUE(chain_length == 2 || chain_length == 3);
// TODO(b/191361618): Once StrongBox implementations use a correctly-issued
// certificate chain, do not skip issuers matching.
EXPECT_TRUE(ChainSignaturesAreValid(cert_chain_, /* strict_issuer_check= */ false));
AuthorizationSet sw_enforced = SwEnforcedAuthorizations(key_characteristics);
EXPECT_TRUE(verify_attestation_record("challenge", "foo", sw_enforced, hw_enforced,

5
security/keymint/aidl/vts/functional/KeyMintAidlTestBase.cpp
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@@ -1493,7 +1493,8 @@ AuthorizationSet SwEnforcedAuthorizations(const vector<KeyCharacteristics>& key_
return authList;
}
AssertionResult ChainSignaturesAreValid(const vector<Certificate>& chain) {
AssertionResult ChainSignaturesAreValid(const vector<Certificate>& chain,
bool strict_issuer_check) {
std::stringstream cert_data;
for (size_t i = 0; i < chain.size(); ++i) {
@@ -1520,7 +1521,7 @@ AssertionResult ChainSignaturesAreValid(const vector<Certificate>& chain) {
string cert_issuer = x509NameToStr(X509_get_issuer_name(key_cert.get()));
string signer_subj = x509NameToStr(X509_get_subject_name(signing_cert.get()));
if (cert_issuer != signer_subj) {
if (cert_issuer != signer_subj && strict_issuer_check) {
return AssertionFailure() << "Cert " << i << " has wrong issuer.\n"
<< " Signer subject is " << signer_subj
<< " Issuer subject is " << cert_issuer << endl

3
security/keymint/aidl/vts/functional/KeyMintAidlTestBase.h
View File

@@ -349,7 +349,8 @@ void p256_pub_key(const vector<uint8_t>& coseKeyData, EVP_PKEY_Ptr* signingKey);
AuthorizationSet HwEnforcedAuthorizations(const vector<KeyCharacteristics>& key_characteristics);
AuthorizationSet SwEnforcedAuthorizations(const vector<KeyCharacteristics>& key_characteristics);
::testing::AssertionResult ChainSignaturesAreValid(const vector<Certificate>& chain);
::testing::AssertionResult ChainSignaturesAreValid(const vector<Certificate>& chain,
bool strict_issuer_check = true);
#define INSTANTIATE_KEYMINT_AIDL_TEST(name) \
INSTANTIATE_TEST_SUITE_P(PerInstance, name, \