Identity Credential: Switch default implementation to use libeic.

Introduce platform-neutral C library ("libeic") which can be used to
implement an Identity Credential Trusted Application/Applet in Secure
Hardware.

The libeic library is intentionally low-level, has no dependencies
(not even libc), uses very little run-time memory (less than 500 bytes
during a provisioning or presentation session), and doesn't
dynamically allocate any memory. Crypto routines are provided by the
library user through a simple crypto interface defined in EicOps.

Also provide an Android-side HAL implementation designed to
communicate with libeic running in Secure Hardware outside
Android. Abstract out communications between HAL and TA in a couple of
SecureHardwareProxy* classes which mimic libeic 1:1.

The default implementation of the HAL is a combination of the
aforementioned HAL using libeic in-process backed by BoringSSL for the
crypto bits.

Test: atest VtsHalIdentityTargetTest
Test: atest android.security.identity.cts
Bug: 170146643
Change-Id: I3bf43fa7fd9362f94023052591801f2094a04607

1 files changed, 836 insertions, 0 deletions

diff --git a/identity/aidl/default/common/IdentityCredential.cpp b/identity/aidl/default/common/IdentityCredential.cpp
new file mode 100644
index 0000000000..270fcfa8d0
--- /dev/null
+++ b/identity/aidl/default/common/IdentityCredential.cpp
@@ -0,0 +1,836 @@
+/*
+ * Copyright 2019, 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.
+ */
+
+#define LOG_TAG "IdentityCredential"
+
+#include "IdentityCredential.h"
+#include "IdentityCredentialStore.h"
+
+#include <android/hardware/identity/support/IdentityCredentialSupport.h>
+
+#include <string.h>
+
+#include <android-base/logging.h>
+#include <android-base/stringprintf.h>
+
+#include <cppbor.h>
+#include <cppbor_parse.h>
+
+#include "FakeSecureHardwareProxy.h"
+
+namespace aidl::android::hardware::identity {
+
+using ::aidl::android::hardware::keymaster::Timestamp;
+using ::android::base::StringPrintf;
+using ::std::optional;
+
+using namespace ::android::hardware::identity;
+
+int IdentityCredential::initialize() {
+    if (credentialData_.size() == 0) {
+        LOG(ERROR) << "CredentialData is empty";
+        return IIdentityCredentialStore::STATUS_INVALID_DATA;
+    }
+    auto [item, _, message] = cppbor::parse(credentialData_);
+    if (item == nullptr) {
+        LOG(ERROR) << "CredentialData is not valid CBOR: " << message;
+        return IIdentityCredentialStore::STATUS_INVALID_DATA;
+    }
+
+    const cppbor::Array* arrayItem = item->asArray();
+    if (arrayItem == nullptr || arrayItem->size() != 3) {
+        LOG(ERROR) << "CredentialData is not an array with three elements";
+        return IIdentityCredentialStore::STATUS_INVALID_DATA;
+    }
+
+    const cppbor::Tstr* docTypeItem = (*arrayItem)[0]->asTstr();
+    const cppbor::Bool* testCredentialItem =
+            ((*arrayItem)[1]->asSimple() != nullptr ? ((*arrayItem)[1]->asSimple()->asBool())
+                                                    : nullptr);
+    const cppbor::Bstr* encryptedCredentialKeysItem = (*arrayItem)[2]->asBstr();
+    if (docTypeItem == nullptr || testCredentialItem == nullptr ||
+        encryptedCredentialKeysItem == nullptr) {
+        LOG(ERROR) << "CredentialData unexpected item types";
+        return IIdentityCredentialStore::STATUS_INVALID_DATA;
+    }
+
+    docType_ = docTypeItem->value();
+    testCredential_ = testCredentialItem->value();
+
+    const vector<uint8_t>& encryptedCredentialKeys = encryptedCredentialKeysItem->value();
+
+    if (encryptedCredentialKeys.size() != 80) {
+        LOG(ERROR) << "Unexpected size for encrypted CredentialKeys";
+        return IIdentityCredentialStore::STATUS_INVALID_DATA;
+    }
+
+    if (!hwProxy_->initialize(testCredential_, docType_, encryptedCredentialKeys)) {
+        LOG(ERROR) << "hwProxy->initialize failed";
+        return false;
+    }
+
+    return IIdentityCredentialStore::STATUS_OK;
+}
+
+ndk::ScopedAStatus IdentityCredential::deleteCredential(
+        vector<uint8_t>* outProofOfDeletionSignature) {
+    cppbor::Array array = {"ProofOfDeletion", docType_, testCredential_};
+    vector<uint8_t> proofOfDeletionCbor = array.encode();
+    vector<uint8_t> podDigest = support::sha256(proofOfDeletionCbor);
+
+    optional<vector<uint8_t>> signatureOfToBeSigned =
+            hwProxy_->deleteCredential(docType_, proofOfDeletionCbor.size());
+    if (!signatureOfToBeSigned) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Error signing ProofOfDeletion"));
+    }
+
+    optional<vector<uint8_t>> signature =
+            support::coseSignEcDsaWithSignature(signatureOfToBeSigned.value(),
+                                                proofOfDeletionCbor,  // data
+                                                {});                  // certificateChain
+    if (!signature) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Error signing data"));
+    }
+
+    *outProofOfDeletionSignature = signature.value();
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus IdentityCredential::createEphemeralKeyPair(vector<uint8_t>* outKeyPair) {
+    optional<vector<uint8_t>> ephemeralPriv = hwProxy_->createEphemeralKeyPair();
+    if (!ephemeralPriv) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Error creating ephemeral key"));
+    }
+    optional<vector<uint8_t>> keyPair = support::ecPrivateKeyToKeyPair(ephemeralPriv.value());
+    if (!keyPair) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Error creating ephemeral key-pair"));
+    }
+
+    // Stash public key of this key-pair for later check in startRetrieval().
+    optional<vector<uint8_t>> publicKey = support::ecKeyPairGetPublicKey(keyPair.value());
+    if (!publicKey) {
+        LOG(ERROR) << "Error getting public part of ephemeral key pair";
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED,
+                "Error getting public part of ephemeral key pair"));
+    }
+    ephemeralPublicKey_ = publicKey.value();
+
+    *outKeyPair = keyPair.value();
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus IdentityCredential::setReaderEphemeralPublicKey(
+        const vector<uint8_t>& publicKey) {
+    readerPublicKey_ = publicKey;
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus IdentityCredential::createAuthChallenge(int64_t* outChallenge) {
+    optional<uint64_t> challenge = hwProxy_->createAuthChallenge();
+    if (!challenge) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Error generating challenge"));
+    }
+    *outChallenge = challenge.value();
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus IdentityCredential::setRequestedNamespaces(
+        const vector<RequestNamespace>& requestNamespaces) {
+    requestNamespaces_ = requestNamespaces;
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus IdentityCredential::setVerificationToken(
+        const VerificationToken& verificationToken) {
+    verificationToken_ = verificationToken;
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus IdentityCredential::startRetrieval(
+        const vector<SecureAccessControlProfile>& accessControlProfiles,
+        const HardwareAuthToken& authToken, const vector<uint8_t>& itemsRequest,
+        const vector<uint8_t>& signingKeyBlob, const vector<uint8_t>& sessionTranscript,
+        const vector<uint8_t>& readerSignature, const vector<int32_t>& requestCounts) {
+    std::unique_ptr<cppbor::Item> sessionTranscriptItem;
+    if (sessionTranscript.size() > 0) {
+        auto [item, _, message] = cppbor::parse(sessionTranscript);
+        if (item == nullptr) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_INVALID_DATA,
+                    "SessionTranscript contains invalid CBOR"));
+        }
+        sessionTranscriptItem = std::move(item);
+    }
+    if (numStartRetrievalCalls_ > 0) {
+        if (sessionTranscript_ != sessionTranscript) {
+            LOG(ERROR) << "Session Transcript changed";
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_SESSION_TRANSCRIPT_MISMATCH,
+                    "Passed-in SessionTranscript doesn't match previously used SessionTranscript"));
+        }
+    }
+    sessionTranscript_ = sessionTranscript;
+
+    // This resets various state in the TA...
+    if (!hwProxy_->startRetrieveEntries()) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Error starting retrieving entries"));
+    }
+
+    optional<vector<uint8_t>> signatureOfToBeSigned;
+    if (readerSignature.size() > 0) {
+        signatureOfToBeSigned = support::coseSignGetSignature(readerSignature);
+        if (!signatureOfToBeSigned) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_READER_SIGNATURE_CHECK_FAILED,
+                    "Error extracting signatureOfToBeSigned from COSE_Sign1"));
+        }
+    }
+
+    // Feed the auth token to secure hardware.
+    if (!hwProxy_->setAuthToken(authToken.challenge, authToken.userId, authToken.authenticatorId,
+                                int(authToken.authenticatorType), authToken.timestamp.milliSeconds,
+                                authToken.mac, verificationToken_.challenge,
+                                verificationToken_.timestamp.milliSeconds,
+                                int(verificationToken_.securityLevel), verificationToken_.mac)) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_INVALID_DATA, "Invalid Auth Token"));
+    }
+
+    // We'll be feeding ACPs interleaved with certificates from the reader
+    // certificate chain...
+    vector<SecureAccessControlProfile> remainingAcps = accessControlProfiles;
+
+    // ... and we'll use those ACPs to build up a 32-bit mask indicating which
+    // of the possible 32 ACPs grants access.
+    uint32_t accessControlProfileMask = 0;
+
+    // If there is a signature, validate that it was made with the top-most key in the
+    // certificate chain embedded in the COSE_Sign1 structure.
+    optional<vector<uint8_t>> readerCertificateChain;
+    if (readerSignature.size() > 0) {
+        readerCertificateChain = support::coseSignGetX5Chain(readerSignature);
+        if (!readerCertificateChain) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_READER_SIGNATURE_CHECK_FAILED,
+                    "Unable to get reader certificate chain from COSE_Sign1"));
+        }
+
+        // First, feed all the reader certificates to the secure hardware. We start
+        // at the end..
+        optional<vector<vector<uint8_t>>> splitCerts =
+                support::certificateChainSplit(readerCertificateChain.value());
+        if (!splitCerts || splitCerts.value().size() == 0) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_READER_SIGNATURE_CHECK_FAILED,
+                    "Error splitting certificate chain from COSE_Sign1"));
+        }
+        for (ssize_t n = splitCerts.value().size() - 1; n >= 0; --n) {
+            const vector<uint8_t>& x509Cert = splitCerts.value()[n];
+            if (!hwProxy_->pushReaderCert(x509Cert)) {
+                return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                        IIdentityCredentialStore::STATUS_READER_SIGNATURE_CHECK_FAILED,
+                        StringPrintf("Error validating reader certificate %zd", n).c_str()));
+            }
+
+            // If we have ACPs for that particular certificate, send them to the
+            // TA right now...
+            //
+            // Remember in this case certificate equality is done by comparing public keys,
+            // not bitwise comparison of the certificates.
+            //
+            optional<vector<uint8_t>> x509CertPubKey =
+                    support::certificateChainGetTopMostKey(x509Cert);
+            if (!x509CertPubKey) {
+                return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                        IIdentityCredentialStore::STATUS_FAILED,
+                        StringPrintf("Error getting public key from reader certificate %zd", n)
+                                .c_str()));
+            }
+            vector<SecureAccessControlProfile>::iterator it = remainingAcps.begin();
+            while (it != remainingAcps.end()) {
+                const SecureAccessControlProfile& profile = *it;
+                if (profile.readerCertificate.encodedCertificate.size() == 0) {
+                    ++it;
+                    continue;
+                }
+                optional<vector<uint8_t>> profilePubKey = support::certificateChainGetTopMostKey(
+                        profile.readerCertificate.encodedCertificate);
+                if (!profilePubKey) {
+                    return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                            IIdentityCredentialStore::STATUS_FAILED,
+                            "Error getting public key from profile"));
+                }
+                if (profilePubKey.value() == x509CertPubKey.value()) {
+                    optional<bool> res = hwProxy_->validateAccessControlProfile(
+                            profile.id, profile.readerCertificate.encodedCertificate,
+                            profile.userAuthenticationRequired, profile.timeoutMillis,
+                            profile.secureUserId, profile.mac);
+                    if (!res) {
+                        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                                IIdentityCredentialStore::STATUS_INVALID_DATA,
+                                "Error validating access control profile"));
+                    }
+                    if (res.value()) {
+                        accessControlProfileMask |= (1 << profile.id);
+                    }
+                    it = remainingAcps.erase(it);
+                } else {
+                    ++it;
+                }
+            }
+        }
+
+        // ... then pass the request message and have the TA check it's signed by the
+        // key in last certificate we pushed.
+        if (sessionTranscript.size() > 0 && itemsRequest.size() > 0 && readerSignature.size() > 0) {
+            optional<vector<uint8_t>> tbsSignature = support::coseSignGetSignature(readerSignature);
+            if (!tbsSignature) {
+                return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                        IIdentityCredentialStore::STATUS_READER_SIGNATURE_CHECK_FAILED,
+                        "Error extracting toBeSigned from COSE_Sign1"));
+            }
+            optional<int> coseSignAlg = support::coseSignGetAlg(readerSignature);
+            if (!coseSignAlg) {
+                return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                        IIdentityCredentialStore::STATUS_READER_SIGNATURE_CHECK_FAILED,
+                        "Error extracting signature algorithm from COSE_Sign1"));
+            }
+            if (!hwProxy_->validateRequestMessage(sessionTranscript, itemsRequest,
+                                                  coseSignAlg.value(), tbsSignature.value())) {
+                return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                        IIdentityCredentialStore::STATUS_READER_SIGNATURE_CHECK_FAILED,
+                        "readerMessage is not signed by top-level certificate"));
+            }
+        }
+    }
+
+    // Feed remaining access control profiles...
+    for (const SecureAccessControlProfile& profile : remainingAcps) {
+        optional<bool> res = hwProxy_->validateAccessControlProfile(
+                profile.id, profile.readerCertificate.encodedCertificate,
+                profile.userAuthenticationRequired, profile.timeoutMillis, profile.secureUserId,
+                profile.mac);
+        if (!res) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_INVALID_DATA,
+                    "Error validating access control profile"));
+        }
+        if (res.value()) {
+            accessControlProfileMask |= (1 << profile.id);
+        }
+    }
+
+    // TODO: move this check to the TA
+#if 1
+    // To prevent replay-attacks, we check that the public part of the ephemeral
+    // key we previously created, is present in the DeviceEngagement part of
+    // SessionTranscript as a COSE_Key, in uncompressed form.
+    //
+    // We do this by just searching for the X and Y coordinates.
+    if (sessionTranscript.size() > 0) {
+        auto [getXYSuccess, ePubX, ePubY] = support::ecPublicKeyGetXandY(ephemeralPublicKey_);
+        if (!getXYSuccess) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_EPHEMERAL_PUBLIC_KEY_NOT_FOUND,
+                    "Error extracting X and Y from ePub"));
+        }
+        if (sessionTranscript.size() > 0 &&
+            !(memmem(sessionTranscript.data(), sessionTranscript.size(), ePubX.data(),
+                     ePubX.size()) != nullptr &&
+              memmem(sessionTranscript.data(), sessionTranscript.size(), ePubY.data(),
+                     ePubY.size()) != nullptr)) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_EPHEMERAL_PUBLIC_KEY_NOT_FOUND,
+                    "Did not find ephemeral public key's X and Y coordinates in "
+                    "SessionTranscript (make sure leading zeroes are not used)"));
+        }
+    }
+#endif
+
+    // itemsRequest: If non-empty, contains request data that may be signed by the
+    // reader.  The content can be defined in the way appropriate for the
+    // credential, but there are three requirements that must be met to work with
+    // this HAL:
+    if (itemsRequest.size() > 0) {
+        // 1. The content must be a CBOR-encoded structure.
+        auto [item, _, message] = cppbor::parse(itemsRequest);
+        if (item == nullptr) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_INVALID_ITEMS_REQUEST_MESSAGE,
+                    "Error decoding CBOR in itemsRequest"));
+        }
+
+        // 2. The CBOR structure must be a map.
+        const cppbor::Map* map = item->asMap();
+        if (map == nullptr) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_INVALID_ITEMS_REQUEST_MESSAGE,
+                    "itemsRequest is not a CBOR map"));
+        }
+
+        // 3. The map must contain a key "nameSpaces" whose value contains a map, as described in
+        //    the example below.
+        //
+        //   NameSpaces = {
+        //     + NameSpace => DataElements ; Requested data elements for each NameSpace
+        //   }
+        //
+        //   NameSpace = tstr
+        //
+        //   DataElements = {
+        //     + DataElement => IntentToRetain
+        //   }
+        //
+        //   DataElement = tstr
+        //   IntentToRetain = bool
+        //
+        // Here's an example of an |itemsRequest| CBOR value satisfying above requirements 1.
+        // through 3.:
+        //
+        //    {
+        //        'docType' : 'org.iso.18013-5.2019',
+        //        'nameSpaces' : {
+        //            'org.iso.18013-5.2019' : {
+        //                'Last name' : false,
+        //                'Birth date' : false,
+        //                'First name' : false,
+        //                'Home address' : true
+        //            },
+        //            'org.aamva.iso.18013-5.2019' : {
+        //                'Real Id' : false
+        //            }
+        //        }
+        //    }
+        //
+        const cppbor::Map* nsMap = nullptr;
+        for (size_t n = 0; n < map->size(); n++) {
+            const auto& [keyItem, valueItem] = (*map)[n];
+            if (keyItem->type() == cppbor::TSTR && keyItem->asTstr()->value() == "nameSpaces" &&
+                valueItem->type() == cppbor::MAP) {
+                nsMap = valueItem->asMap();
+                break;
+            }
+        }
+        if (nsMap == nullptr) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_INVALID_ITEMS_REQUEST_MESSAGE,
+                    "No nameSpaces map in top-most map"));
+        }
+
+        for (size_t n = 0; n < nsMap->size(); n++) {
+            auto [nsKeyItem, nsValueItem] = (*nsMap)[n];
+            const cppbor::Tstr* nsKey = nsKeyItem->asTstr();
+            const cppbor::Map* nsInnerMap = nsValueItem->asMap();
+            if (nsKey == nullptr || nsInnerMap == nullptr) {
+                return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                        IIdentityCredentialStore::STATUS_INVALID_ITEMS_REQUEST_MESSAGE,
+                        "Type mismatch in nameSpaces map"));
+            }
+            string requestedNamespace = nsKey->value();
+            set<string> requestedKeys;
+            for (size_t m = 0; m < nsInnerMap->size(); m++) {
+                const auto& [innerMapKeyItem, innerMapValueItem] = (*nsInnerMap)[m];
+                const cppbor::Tstr* nameItem = innerMapKeyItem->asTstr();
+                const cppbor::Simple* simple = innerMapValueItem->asSimple();
+                const cppbor::Bool* intentToRetainItem =
+                        (simple != nullptr) ? simple->asBool() : nullptr;
+                if (nameItem == nullptr || intentToRetainItem == nullptr) {
+                    return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                            IIdentityCredentialStore::STATUS_INVALID_ITEMS_REQUEST_MESSAGE,
+                            "Type mismatch in value in nameSpaces map"));
+                }
+                requestedKeys.insert(nameItem->value());
+            }
+            requestedNameSpacesAndNames_[requestedNamespace] = requestedKeys;
+        }
+    }
+
+    deviceNameSpacesMap_ = cppbor::Map();
+    currentNameSpaceDeviceNameSpacesMap_ = cppbor::Map();
+
+    requestCountsRemaining_ = requestCounts;
+    currentNameSpace_ = "";
+
+    itemsRequest_ = itemsRequest;
+    signingKeyBlob_ = signingKeyBlob;
+
+    // calculate the size of DeviceNameSpaces. We need to know it ahead of time.
+    calcDeviceNameSpacesSize(accessControlProfileMask);
+
+    // Count the number of non-empty namespaces
+    size_t numNamespacesWithValues = 0;
+    for (size_t n = 0; n < expectedNumEntriesPerNamespace_.size(); n++) {
+        if (expectedNumEntriesPerNamespace_[n] > 0) {
+            numNamespacesWithValues += 1;
+        }
+    }
+
+    // Finally, pass info so the HMAC key can be derived and the TA can start
+    // creating the DeviceNameSpaces CBOR...
+    if (sessionTranscript_.size() > 0 && readerPublicKey_.size() > 0 && signingKeyBlob.size() > 0) {
+        // We expect the reader ephemeral public key to be same size and curve
+        // as the ephemeral key we generated (e.g. P-256 key), otherwise ECDH
+        // won't work. So its length should be 65 bytes and it should be
+        // starting with 0x04.
+        if (readerPublicKey_.size() != 65 || readerPublicKey_[0] != 0x04) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_FAILED,
+                    "Reader public key is not in expected format"));
+        }
+        vector<uint8_t> pubKeyP256(readerPublicKey_.begin() + 1, readerPublicKey_.end());
+        if (!hwProxy_->calcMacKey(sessionTranscript_, pubKeyP256, signingKeyBlob, docType_,
+                                  numNamespacesWithValues, expectedDeviceNameSpacesSize_)) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_FAILED, "Error starting retrieving entries"));
+        }
+    }
+
+    numStartRetrievalCalls_ += 1;
+    return ndk::ScopedAStatus::ok();
+}
+
+size_t cborNumBytesForLength(size_t length) {
+    if (length < 24) {
+        return 0;
+    } else if (length <= 0xff) {
+        return 1;
+    } else if (length <= 0xffff) {
+        return 2;
+    } else if (length <= 0xffffffff) {
+        return 4;
+    }
+    return 8;
+}
+
+size_t cborNumBytesForTstr(const string& value) {
+    return 1 + cborNumBytesForLength(value.size()) + value.size();
+}
+
+void IdentityCredential::calcDeviceNameSpacesSize(uint32_t accessControlProfileMask) {
+    /*
+     * This is how DeviceNameSpaces is defined:
+     *
+     *        DeviceNameSpaces = {
+     *            * NameSpace => DeviceSignedItems
+     *        }
+     *        DeviceSignedItems = {
+     *            + DataItemName => DataItemValue
+     *        }
+     *
+     *        Namespace = tstr
+     *        DataItemName = tstr
+     *        DataItemValue = any
+     *
+     * This function will calculate its length using knowledge of how CBOR is
+     * encoded.
+     */
+    size_t ret = 0;
+    vector<unsigned int> numEntriesPerNamespace;
+    for (const RequestNamespace& rns : requestNamespaces_) {
+        vector<RequestDataItem> itemsToInclude;
+
+        for (const RequestDataItem& rdi : rns.items) {
+            // If we have a CBOR request message, skip if item isn't in it
+            if (itemsRequest_.size() > 0) {
+                const auto& it = requestedNameSpacesAndNames_.find(rns.namespaceName);
+                if (it == requestedNameSpacesAndNames_.end()) {
+                    continue;
+                }
+                const set<string>& dataItemNames = it->second;
+                if (dataItemNames.find(rdi.name) == dataItemNames.end()) {
+                    continue;
+                }
+            }
+
+            // Access is granted if at least one of the profiles grants access.
+            //
+            // If an item is configured without any profiles, access is denied.
+            //
+            bool authorized = false;
+            for (auto id : rdi.accessControlProfileIds) {
+                if (accessControlProfileMask & (1 << id)) {
+                    authorized = true;
+                    break;
+                }
+            }
+            if (!authorized) {
+                continue;
+            }
+
+            itemsToInclude.push_back(rdi);
+        }
+
+        numEntriesPerNamespace.push_back(itemsToInclude.size());
+
+        // If no entries are to be in the namespace, we don't include it in
+        // the CBOR...
+        if (itemsToInclude.size() == 0) {
+            continue;
+        }
+
+        // Key: NameSpace
+        ret += cborNumBytesForTstr(rns.namespaceName);
+
+        // Value: Open the DeviceSignedItems map
+        ret += 1 + cborNumBytesForLength(itemsToInclude.size());
+
+        for (const RequestDataItem& item : itemsToInclude) {
+            // Key: DataItemName
+            ret += cborNumBytesForTstr(item.name);
+
+            // Value: DataItemValue - entryData.size is the length of serialized CBOR so we use
+            // that.
+            ret += item.size;
+        }
+    }
+
+    // Now that we know the number of namespaces with values, we know how many
+    // bytes the DeviceNamespaces map in the beginning is going to take up.
+    ret += 1 + cborNumBytesForLength(numEntriesPerNamespace.size());
+
+    expectedDeviceNameSpacesSize_ = ret;
+    expectedNumEntriesPerNamespace_ = numEntriesPerNamespace;
+}
+
+ndk::ScopedAStatus IdentityCredential::startRetrieveEntryValue(
+        const string& nameSpace, const string& name, int32_t entrySize,
+        const vector<int32_t>& accessControlProfileIds) {
+    if (name.empty()) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_INVALID_DATA, "Name cannot be empty"));
+    }
+    if (nameSpace.empty()) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_INVALID_DATA, "Name space cannot be empty"));
+    }
+
+    if (requestCountsRemaining_.size() == 0) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_INVALID_DATA,
+                "No more name spaces left to go through"));
+    }
+
+    bool newNamespace;
+    if (currentNameSpace_ == "") {
+        // First call.
+        currentNameSpace_ = nameSpace;
+        newNamespace = true;
+    }
+
+    if (nameSpace == currentNameSpace_) {
+        // Same namespace.
+        if (requestCountsRemaining_[0] == 0) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_INVALID_DATA,
+                    "No more entries to be retrieved in current name space"));
+        }
+        requestCountsRemaining_[0] -= 1;
+    } else {
+        // New namespace.
+        if (requestCountsRemaining_[0] != 0) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_INVALID_DATA,
+                    "Moved to new name space but one or more entries need to be retrieved "
+                    "in current name space"));
+        }
+        if (currentNameSpaceDeviceNameSpacesMap_.size() > 0) {
+            deviceNameSpacesMap_.add(currentNameSpace_,
+                                     std::move(currentNameSpaceDeviceNameSpacesMap_));
+        }
+        currentNameSpaceDeviceNameSpacesMap_ = cppbor::Map();
+
+        requestCountsRemaining_.erase(requestCountsRemaining_.begin());
+        currentNameSpace_ = nameSpace;
+        newNamespace = true;
+    }
+
+    // It's permissible to have an empty itemsRequest... but if non-empty you can
+    // only request what was specified in said itemsRequest. Enforce that.
+    if (itemsRequest_.size() > 0) {
+        const auto& it = requestedNameSpacesAndNames_.find(nameSpace);
+        if (it == requestedNameSpacesAndNames_.end()) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_NOT_IN_REQUEST_MESSAGE,
+                    "Name space was not requested in startRetrieval"));
+        }
+        const set<string>& dataItemNames = it->second;
+        if (dataItemNames.find(name) == dataItemNames.end()) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_NOT_IN_REQUEST_MESSAGE,
+                    "Data item name in name space was not requested in startRetrieval"));
+        }
+    }
+
+    unsigned int newNamespaceNumEntries = 0;
+    if (newNamespace) {
+        if (expectedNumEntriesPerNamespace_.size() == 0) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_INVALID_DATA,
+                    "No more populated name spaces left to go through"));
+        }
+        newNamespaceNumEntries = expectedNumEntriesPerNamespace_[0];
+        expectedNumEntriesPerNamespace_.erase(expectedNumEntriesPerNamespace_.begin());
+    }
+
+    // Access control is enforced in the secure hardware.
+    //
+    // ... except for STATUS_NOT_IN_REQUEST_MESSAGE, that's handled above (TODO:
+    // consolidate).
+    //
+    AccessCheckResult res = hwProxy_->startRetrieveEntryValue(
+            nameSpace, name, newNamespaceNumEntries, entrySize, accessControlProfileIds);
+    switch (res) {
+        case AccessCheckResult::kOk:
+            /* Do nothing. */
+            break;
+        case AccessCheckResult::kFailed:
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_FAILED,
+                    "Access control check failed (failed)"));
+            break;
+        case AccessCheckResult::kNoAccessControlProfiles:
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_NO_ACCESS_CONTROL_PROFILES,
+                    "Access control check failed (no access control profiles)"));
+            break;
+        case AccessCheckResult::kUserAuthenticationFailed:
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_USER_AUTHENTICATION_FAILED,
+                    "Access control check failed (user auth)"));
+            break;
+        case AccessCheckResult::kReaderAuthenticationFailed:
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_READER_AUTHENTICATION_FAILED,
+                    "Access control check failed (reader auth)"));
+            break;
+    }
+
+    currentName_ = name;
+    currentAccessControlProfileIds_ = accessControlProfileIds;
+    entryRemainingBytes_ = entrySize;
+    entryValue_.resize(0);
+
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus IdentityCredential::retrieveEntryValue(const vector<uint8_t>& encryptedContent,
+                                                          vector<uint8_t>* outContent) {
+    optional<vector<uint8_t>> content = hwProxy_->retrieveEntryValue(
+            encryptedContent, currentNameSpace_, currentName_, currentAccessControlProfileIds_);
+    if (!content) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_INVALID_DATA, "Error decrypting data"));
+    }
+
+    size_t chunkSize = content.value().size();
+
+    if (chunkSize > entryRemainingBytes_) {
+        LOG(ERROR) << "Retrieved chunk of size " << chunkSize
+                   << " is bigger than remaining space of size " << entryRemainingBytes_;
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_INVALID_DATA,
+                "Retrieved chunk is bigger than remaining space"));
+    }
+
+    entryRemainingBytes_ -= chunkSize;
+    if (entryRemainingBytes_ > 0) {
+        if (chunkSize != IdentityCredentialStore::kGcmChunkSize) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_INVALID_DATA,
+                    "Retrieved non-final chunk of size which isn't kGcmChunkSize"));
+        }
+    }
+
+    entryValue_.insert(entryValue_.end(), content.value().begin(), content.value().end());
+
+    if (entryRemainingBytes_ == 0) {
+        auto [entryValueItem, _, message] = cppbor::parse(entryValue_);
+        if (entryValueItem == nullptr) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_INVALID_DATA,
+                    "Retrieved data which is invalid CBOR"));
+        }
+        currentNameSpaceDeviceNameSpacesMap_.add(currentName_, std::move(entryValueItem));
+    }
+
+    *outContent = content.value();
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus IdentityCredential::finishRetrieval(vector<uint8_t>* outMac,
+                                                       vector<uint8_t>* outDeviceNameSpaces) {
+    if (currentNameSpaceDeviceNameSpacesMap_.size() > 0) {
+        deviceNameSpacesMap_.add(currentNameSpace_,
+                                 std::move(currentNameSpaceDeviceNameSpacesMap_));
+    }
+    vector<uint8_t> encodedDeviceNameSpaces = deviceNameSpacesMap_.encode();
+
+    if (encodedDeviceNameSpaces.size() != expectedDeviceNameSpacesSize_) {
+        LOG(ERROR) << "encodedDeviceNameSpaces is " << encodedDeviceNameSpaces.size() << " bytes, "
+                   << "was expecting " << expectedDeviceNameSpacesSize_;
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_INVALID_DATA,
+                StringPrintf(
+                        "Unexpected CBOR size %zd for encodedDeviceNameSpaces, was expecting %zd",
+                        encodedDeviceNameSpaces.size(), expectedDeviceNameSpacesSize_)
+                        .c_str()));
+    }
+
+    // If there's no signing key or no sessionTranscript or no reader ephemeral
+    // public key, we return the empty MAC.
+    optional<vector<uint8_t>> mac;
+    if (signingKeyBlob_.size() > 0 && sessionTranscript_.size() > 0 &&
+        readerPublicKey_.size() > 0) {
+        optional<vector<uint8_t>> digestToBeMaced = hwProxy_->finishRetrieval();
+        if (!digestToBeMaced || digestToBeMaced.value().size() != 32) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_INVALID_DATA,
+                    "Error generating digestToBeMaced"));
+        }
+        // Now construct COSE_Mac0 from the returned MAC...
+        mac = support::coseMacWithDigest(digestToBeMaced.value(), {} /* data */);
+    }
+
+    *outMac = mac.value_or(vector<uint8_t>({}));
+    *outDeviceNameSpaces = encodedDeviceNameSpaces;
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus IdentityCredential::generateSigningKeyPair(
+        vector<uint8_t>* outSigningKeyBlob, Certificate* outSigningKeyCertificate) {
+    time_t now = time(NULL);
+    optional<pair<vector<uint8_t>, vector<uint8_t>>> pair =
+            hwProxy_->generateSigningKeyPair(docType_, now);
+    if (!pair) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Error creating signingKey"));
+    }
+
+    *outSigningKeyCertificate = Certificate();
+    outSigningKeyCertificate->encodedCertificate = pair->first;
+
+    *outSigningKeyBlob = pair->second;
+    return ndk::ScopedAStatus::ok();
+}
+
+}  // namespace aidl::android::hardware::identity