trusty_keymaster_context.cpp

/*
 * Copyright 2015 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 "trusty_keymaster_context.h"
#include "secure_storage_manager.h"

#include <lib/hwkey/hwkey.h>
#include <lib/rng/trusty_rng.h>

#include <keymaster/android_keymaster_utils.h>
#include <keymaster/contexts/soft_attestation_cert.h>
#include <keymaster/key_blob_utils/auth_encrypted_key_blob.h>
#include <keymaster/key_blob_utils/ocb_utils.h>
#include <keymaster/km_openssl/aes_key.h>
#include <keymaster/km_openssl/asymmetric_key.h>
#include <keymaster/km_openssl/attestation_utils.h>
#include <keymaster/km_openssl/certificate_utils.h>
#include <keymaster/km_openssl/ec_key_factory.h>
#include <keymaster/km_openssl/hmac_key.h>
#include <keymaster/km_openssl/openssl_err.h>
#include <keymaster/km_openssl/rsa_key_factory.h>
#include <keymaster/km_openssl/triple_des_key.h>
#include <keymaster/logger.h>
#include <keymaster/operation.h>
#include <keymaster/wrapped_key.h>

#include "trusty_aes_key.h"

#ifdef KEYMASTER_DEBUG
#pragma message \
        "Compiling with fake Keymaster Root of Trust values! DO NOT SHIP THIS!"
#endif

// TRUSTY_KM_WRAPPING_KEY_SIZE controls the size of the AES key that is used
// to wrap keys before allowing NS to hold on to them.
// Previously, it had a hardcoded value of 16 bytes, but current guidance is to
// expand this to a 256-bit (32-byte) key.
//
// The plan is to leave old devices as they are, and issue new devices with a
// 32-byte key to ensure compatibility. New devices should set
// TRUSTY_WRAPPING_KEY_SIZE to 32 in their device Makefile to control this.

#ifndef TRUSTY_KM_WRAPPING_KEY_SIZE
#define TRUSTY_KM_WRAPPING_KEY_SIZE 16
#endif

namespace keymaster {

namespace {
static const int kAesKeySize = TRUSTY_KM_WRAPPING_KEY_SIZE;
static const int kCallsBetweenRngReseeds = 32;
static const int kRngReseedSize = 64;
static const uint8_t kMasterKeyDerivationData[kAesKeySize] = "KeymasterMaster";

bool UpgradeIntegerTag(keymaster_tag_t tag,
                       uint32_t value,
                       AuthorizationSet* set,
                       bool* set_changed) {
    int index = set->find(tag);
    if (index == -1) {
        keymaster_key_param_t param;
        param.tag = tag;
        param.integer = value;
        set->push_back(param);
        *set_changed = true;
        return true;
    }

    if (set->params[index].integer > value) {
        return false;
    }

    if (set->params[index].integer != value) {
        set->params[index].integer = value;
        *set_changed = true;
    }
    return true;
}

}  // anonymous namespace

TrustyKeymasterContext::TrustyKeymasterContext()
        : AttestationContext(KmVersion::KEYMASTER_4),
          enforcement_policy_(this),
          rng_initialized_(false),
          calls_since_reseed_(0) {
    LOG_D("Creating TrustyKeymaster", 0);
    rsa_factory_.reset(
            new RsaKeyFactory(*this /* blob_maker */, *this /* context */));
    tdes_factory_.reset(new TripleDesKeyFactory(*this /* blob_maker */,
                                                *this /* random_source */));
    ec_factory_.reset(
            new EcKeyFactory(*this /* blob_maker */, *this /* context */));
    aes_factory_.reset(new TrustyAesKeyFactory(*this /* blob_maker */,
                                               *this /* random_source */));
    hmac_factory_.reset(new HmacKeyFactory(*this /* blob_maker */,
                                           *this /* random_source */));
    verified_boot_key_.Reinitialize("Unbound", 7);
}

const KeyFactory* TrustyKeymasterContext::GetKeyFactory(
        keymaster_algorithm_t algorithm) const {
    switch (algorithm) {
    case KM_ALGORITHM_RSA:
        return rsa_factory_.get();
    case KM_ALGORITHM_EC:
        return ec_factory_.get();
    case KM_ALGORITHM_AES:
        return aes_factory_.get();
    case KM_ALGORITHM_HMAC:
        return hmac_factory_.get();
    case KM_ALGORITHM_TRIPLE_DES:
        return tdes_factory_.get();
    default:
        return nullptr;
    }
}

static keymaster_algorithm_t supported_algorithms[] = {
        KM_ALGORITHM_RSA, KM_ALGORITHM_EC, KM_ALGORITHM_AES, KM_ALGORITHM_HMAC,
        KM_ALGORITHM_TRIPLE_DES};

const keymaster_algorithm_t* TrustyKeymasterContext::GetSupportedAlgorithms(
        size_t* algorithms_count) const {
    *algorithms_count = array_length(supported_algorithms);
    return supported_algorithms;
}

OperationFactory* TrustyKeymasterContext::GetOperationFactory(
        keymaster_algorithm_t algorithm,
        keymaster_purpose_t purpose) const {
    const KeyFactory* key_factory = GetKeyFactory(algorithm);
    if (!key_factory)
        return nullptr;
    return key_factory->GetOperationFactory(purpose);
}

static keymaster_error_t TranslateAuthorizationSetError(
        AuthorizationSet::Error err) {
    switch (err) {
    case AuthorizationSet::OK:
        return KM_ERROR_OK;
    case AuthorizationSet::ALLOCATION_FAILURE:
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;
    case AuthorizationSet::MALFORMED_DATA:
        return KM_ERROR_UNKNOWN_ERROR;
    }
    return KM_ERROR_OK;
}

keymaster_error_t TrustyKeymasterContext::SetAuthorizations(
        const AuthorizationSet& key_description,
        keymaster_key_origin_t origin,
        AuthorizationSet* hw_enforced,
        AuthorizationSet* sw_enforced) const {
    sw_enforced->Clear();
    hw_enforced->Clear();

    for (auto& entry : key_description) {
        switch (entry.tag) {
        case KM_TAG_INVALID:
        case KM_TAG_BOOTLOADER_ONLY:
        case KM_TAG_NONCE:
        case KM_TAG_AUTH_TOKEN:
        case KM_TAG_MAC_LENGTH:
        case KM_TAG_ASSOCIATED_DATA:
        case KM_TAG_UNIQUE_ID:
            return KM_ERROR_INVALID_KEY_BLOB;

        case KM_TAG_ROLLBACK_RESISTANCE:
            // Currently return UNAVAILABLE.
            return KM_ERROR_ROLLBACK_RESISTANCE_UNAVAILABLE;

        case KM_TAG_ROLLBACK_RESISTANT:
        case KM_TAG_APPLICATION_ID:
        case KM_TAG_APPLICATION_DATA:
        case KM_TAG_ALL_APPLICATIONS:
        case KM_TAG_ROOT_OF_TRUST:
        case KM_TAG_ORIGIN:
        case KM_TAG_RESET_SINCE_ID_ROTATION:
        case KM_TAG_ALLOW_WHILE_ON_BODY:
        case KM_TAG_ATTESTATION_CHALLENGE:
        case KM_TAG_OS_VERSION:
        case KM_TAG_OS_PATCHLEVEL:
            // Ignore these.
            break;

        case KM_TAG_PURPOSE:
        case KM_TAG_ALGORITHM:
        case KM_TAG_KEY_SIZE:
        case KM_TAG_RSA_PUBLIC_EXPONENT:
        case KM_TAG_BLOB_USAGE_REQUIREMENTS:
        case KM_TAG_DIGEST:
        case KM_TAG_PADDING:
        case KM_TAG_BLOCK_MODE:
        case KM_TAG_MIN_SECONDS_BETWEEN_OPS:
        case KM_TAG_MAX_USES_PER_BOOT:
        case KM_TAG_USER_SECURE_ID:
        case KM_TAG_NO_AUTH_REQUIRED:
        case KM_TAG_AUTH_TIMEOUT:
        case KM_TAG_CALLER_NONCE:
        case KM_TAG_MIN_MAC_LENGTH:
        case KM_TAG_KDF:
        case KM_TAG_EC_CURVE:
        case KM_TAG_ECIES_SINGLE_HASH_MODE:
        case KM_TAG_TRUSTED_CONFIRMATION_REQUIRED:
#if WITH_HWWSK_SUPPORT
        // keep KM_TAG_STORAGE_KEY is HWWSK service is enabled
        case KM_TAG_STORAGE_KEY:
#endif
            hw_enforced->push_back(entry);
            break;

        case KM_TAG_USER_AUTH_TYPE: {
            keymaster_key_param_t elem = entry;

            // This implementation does support TEE enforced password auth
            elem.enumerated = entry.enumerated & HW_AUTH_PASSWORD;

#if TEE_FINGERPRINT_AUTH_SUPPORTED
            // If HW_AUTH_FINGERPRINT is supported it needs to be included too
            elem.enumerates |= entry.enumerated & HW_AUTH_FINGERPRINT;
#endif
            hw_enforced->push_back(elem);
        } break;

        case KM_TAG_ACTIVE_DATETIME:
        case KM_TAG_ORIGINATION_EXPIRE_DATETIME:
        case KM_TAG_USAGE_EXPIRE_DATETIME:
        case KM_TAG_USER_ID:
        case KM_TAG_ALL_USERS:
        case KM_TAG_CREATION_DATETIME:
        case KM_TAG_INCLUDE_UNIQUE_ID:
        case KM_TAG_EXPORTABLE:
            sw_enforced->push_back(entry);
            break;
        default:
            break;
        }
    }

    hw_enforced->push_back(TAG_ORIGIN, origin);
    // these values will be 0 if not set by bootloader
    hw_enforced->push_back(TAG_OS_VERSION, boot_os_version_);
    hw_enforced->push_back(TAG_OS_PATCHLEVEL, boot_os_patchlevel_);

    if (sw_enforced->is_valid() != AuthorizationSet::OK)
        return TranslateAuthorizationSetError(sw_enforced->is_valid());
    if (hw_enforced->is_valid() != AuthorizationSet::OK)
        return TranslateAuthorizationSetError(hw_enforced->is_valid());
    return KM_ERROR_OK;
}

keymaster_error_t TrustyKeymasterContext::BuildHiddenAuthorizations(
        const AuthorizationSet& input_set,
        AuthorizationSet* hidden) const {
    keymaster_blob_t entry;
    if (input_set.GetTagValue(TAG_APPLICATION_ID, &entry))
        hidden->push_back(TAG_APPLICATION_ID, entry.data, entry.data_length);
    if (input_set.GetTagValue(TAG_APPLICATION_DATA, &entry))
        hidden->push_back(TAG_APPLICATION_DATA, entry.data, entry.data_length);

    // Copy verified boot key, verified boot state, and device lock state to
    // hidden authorization set for binding to key.
    keymaster_key_param_t root_of_trust;
    root_of_trust.tag = KM_TAG_ROOT_OF_TRUST;
    root_of_trust.blob.data = verified_boot_key_.begin();
    root_of_trust.blob.data_length = verified_boot_key_.buffer_size();
    hidden->push_back(root_of_trust);

    root_of_trust.blob.data =
            reinterpret_cast<const uint8_t*>(&verified_boot_state_);
    root_of_trust.blob.data_length = sizeof(verified_boot_state_);
    hidden->push_back(root_of_trust);

    root_of_trust.blob.data = reinterpret_cast<const uint8_t*>(&device_locked_);
    root_of_trust.blob.data_length = sizeof(device_locked_);
    hidden->push_back(root_of_trust);

    return TranslateAuthorizationSetError(hidden->is_valid());
}

keymaster_error_t TrustyKeymasterContext::CreateAuthEncryptedKeyBlob(
        const AuthorizationSet& key_description,
        const KeymasterKeyBlob& key_material,
        const AuthorizationSet& hw_enforced,
        const AuthorizationSet& sw_enforced,
        KeymasterKeyBlob* blob) const {
    AuthorizationSet hidden;
    keymaster_error_t error =
            BuildHiddenAuthorizations(key_description, &hidden);
    if (error != KM_ERROR_OK)
        return error;

    KeymasterKeyBlob master_key;
    error = DeriveMasterKey(&master_key);
    if (error != KM_ERROR_OK)
        return error;

    Buffer nonce(OCB_NONCE_LENGTH);
    Buffer tag(OCB_TAG_LENGTH);
    if (!nonce.peek_write() || !tag.peek_write())
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;

    error = GenerateRandom(nonce.peek_write(), OCB_NONCE_LENGTH);
    if (error != KM_ERROR_OK)
        return error;
    nonce.advance_write(OCB_NONCE_LENGTH);

    KeymasterKeyBlob encrypted_key;
    error = OcbEncryptKey(hw_enforced, sw_enforced, hidden, master_key,
                          key_material, nonce, &encrypted_key, &tag);
    if (error != KM_ERROR_OK)
        return error;

    return SerializeAuthEncryptedBlob(encrypted_key, hw_enforced, sw_enforced,
                                      nonce, tag, blob);
}

keymaster_error_t TrustyKeymasterContext::CreateKeyBlob(
        const AuthorizationSet& key_description,
        keymaster_key_origin_t origin,
        const KeymasterKeyBlob& key_material,
        KeymasterKeyBlob* blob,
        AuthorizationSet* hw_enforced,
        AuthorizationSet* sw_enforced) const {
    keymaster_error_t error = SetAuthorizations(key_description, origin,
                                                hw_enforced, sw_enforced);
    if (error != KM_ERROR_OK)
        return error;

    return CreateAuthEncryptedKeyBlob(key_description, key_material,
                                      *hw_enforced, *sw_enforced, blob);
}

keymaster_error_t TrustyKeymasterContext::UpgradeKeyBlob(
        const KeymasterKeyBlob& key_to_upgrade,
        const AuthorizationSet& upgrade_params,
        KeymasterKeyBlob* upgraded_key) const {
    UniquePtr<Key> key;
    keymaster_error_t error =
            ParseKeyBlob(key_to_upgrade, upgrade_params, &key);
    if (error != KM_ERROR_OK)
        return error;

    bool set_changed = false;

    if (boot_os_version_ == 0) {
        // We need to allow "upgrading" OS version to zero, to support upgrading
        // from proper numbered releases to unnumbered development and preview
        // releases.

        int key_os_version_pos = key->sw_enforced().find(TAG_OS_VERSION);
        if (key_os_version_pos != -1) {
            uint32_t key_os_version =
                    key->sw_enforced()[key_os_version_pos].integer;
            if (key_os_version != 0) {
                key->sw_enforced()[key_os_version_pos].integer =
                        boot_os_version_;
                set_changed = true;
            }
        }
    }

    if (!UpgradeIntegerTag(TAG_OS_VERSION, boot_os_version_,
                           &key->hw_enforced(), &set_changed) ||
        !UpgradeIntegerTag(TAG_OS_PATCHLEVEL, boot_os_patchlevel_,
                           &key->hw_enforced(), &set_changed)) {
        // One of the version fields would have been a downgrade. Not allowed.
        return KM_ERROR_INVALID_ARGUMENT;
    }

    if (!set_changed) {
        // Don't need an upgrade.
        return KM_ERROR_OK;
    }

    return CreateAuthEncryptedKeyBlob(upgrade_params, key->key_material(),
                                      key->hw_enforced(), key->sw_enforced(),
                                      upgraded_key);
}

keymaster_error_t TrustyKeymasterContext::ParseKeyBlob(
        const KeymasterKeyBlob& blob,
        const AuthorizationSet& additional_params,
        UniquePtr<Key>* key) const {
    AuthorizationSet hw_enforced;
    AuthorizationSet sw_enforced;
    KeymasterKeyBlob key_material;
    keymaster_error_t error;

    auto constructKey = [&, this]() mutable -> keymaster_error_t {
        // GetKeyFactory
        if (error != KM_ERROR_OK)
            return error;
        keymaster_algorithm_t algorithm;
        if (!hw_enforced.GetTagValue(TAG_ALGORITHM, &algorithm)) {
            return KM_ERROR_INVALID_ARGUMENT;
        }
        auto factory = GetKeyFactory(algorithm);
        return factory->LoadKey(move(key_material), additional_params,
                                move(hw_enforced), move(sw_enforced), key);
    };

    Buffer nonce, tag;
    KeymasterKeyBlob encrypted_key_material;
    if (!key)
        return KM_ERROR_UNEXPECTED_NULL_POINTER;
    error = DeserializeAuthEncryptedBlob(blob, &encrypted_key_material,
                                         &hw_enforced, &sw_enforced, &nonce,
                                         &tag);
    if (error != KM_ERROR_OK)
        return error;

    if (nonce.available_read() != OCB_NONCE_LENGTH ||
        tag.available_read() != OCB_TAG_LENGTH)
        return KM_ERROR_INVALID_KEY_BLOB;

    KeymasterKeyBlob master_key;
    error = DeriveMasterKey(&master_key);
    if (error != KM_ERROR_OK)
        return error;

    AuthorizationSet hidden;
    error = BuildHiddenAuthorizations(additional_params, &hidden);
    if (error != KM_ERROR_OK)
        return error;

    error = OcbDecryptKey(hw_enforced, sw_enforced, hidden, master_key,
                          encrypted_key_material, nonce, tag, &key_material);
    return constructKey();
}

keymaster_error_t TrustyKeymasterContext::AddRngEntropy(const uint8_t* buf,
                                                        size_t length) const {
    if (trusty_rng_add_entropy(buf, length) != 0)
        return KM_ERROR_UNKNOWN_ERROR;
    return KM_ERROR_OK;
}

bool TrustyKeymasterContext::SeedRngIfNeeded() const {
    if (ShouldReseedRng())
        const_cast<TrustyKeymasterContext*>(this)->ReseedRng();
    return rng_initialized_;
}

bool TrustyKeymasterContext::ShouldReseedRng() const {
    if (!rng_initialized_) {
        LOG_I("RNG not initalized, reseed", 0);
        return true;
    }

    if (++calls_since_reseed_ % kCallsBetweenRngReseeds == 0) {
        LOG_I("Periodic reseed", 0);
        return true;
    }
    return false;
}

bool TrustyKeymasterContext::ReseedRng() {
    UniquePtr<uint8_t[]> rand_seed(new uint8_t[kRngReseedSize]);
    memset(rand_seed.get(), 0, kRngReseedSize);
    if (trusty_rng_hw_rand(rand_seed.get(), kRngReseedSize) != 0) {
        LOG_E("Failed to get bytes from HW RNG", 0);
        return false;
    }
    LOG_I("Reseeding with %d bytes from HW RNG", kRngReseedSize);
    trusty_rng_add_entropy(rand_seed.get(), kRngReseedSize);

    rng_initialized_ = true;
    return true;
}

// Gee wouldn't it be nice if the crypto service headers defined this.
enum DerivationParams {
    DERIVATION_DATA_PARAM = 0,
    OUTPUT_BUFFER_PARAM = 1,
};

keymaster_error_t TrustyKeymasterContext::DeriveMasterKey(
        KeymasterKeyBlob* master_key) const {
    LOG_D("Deriving master key", 0);

    long rc = hwkey_open();
    if (rc < 0) {
        return KM_ERROR_UNKNOWN_ERROR;
    }

    hwkey_session_t session = (hwkey_session_t)rc;

    if (!master_key->Reset(kAesKeySize)) {
        LOG_S("Could not allocate memory for master key buffer", 0);
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;
    }

    uint32_t kdf_version = HWKEY_KDF_VERSION_1;
    rc = hwkey_derive(session, &kdf_version, kMasterKeyDerivationData,
                      master_key->writable_data(), kAesKeySize);

    if (rc < 0) {
        LOG_S("Error deriving master key: %d", rc);
        return KM_ERROR_UNKNOWN_ERROR;
    }

    hwkey_close(session);
    LOG_I("Key derivation complete", 0);
    return KM_ERROR_OK;
}

bool TrustyKeymasterContext::InitializeAuthTokenKey() {
    if (auth_token_key_initialized_)
        return true;

    keymaster_key_blob_t key;
    key.key_material = auth_token_key_;
    key.key_material_size = kAuthTokenKeySize;
    keymaster_error_t error = enforcement_policy_.GetHmacKey(&key);
    if (error == KM_ERROR_OK)
        auth_token_key_initialized_ = true;
    else
        auth_token_key_initialized_ = false;

    return auth_token_key_initialized_;
}

keymaster_error_t TrustyKeymasterContext::GetAuthTokenKey(
        keymaster_key_blob_t* key) const {
    if (!auth_token_key_initialized_ &&
        !const_cast<TrustyKeymasterContext*>(this)->InitializeAuthTokenKey())
        return KM_ERROR_UNKNOWN_ERROR;

    key->key_material = auth_token_key_;
    key->key_material_size = kAuthTokenKeySize;
    return KM_ERROR_OK;
}

keymaster_error_t TrustyKeymasterContext::SetSystemVersion(
        uint32_t os_version,
        uint32_t os_patchlevel) {
    if (!version_info_set_) {
        // Note that version info is now set by Configure, rather than by the
        // bootloader.  This is to ensure that system-only updates can be done,
        // to avoid breaking Project Treble.
        boot_os_version_ = os_version;
        boot_os_patchlevel_ = os_patchlevel;
        version_info_set_ = true;
    }

#ifdef KEYMASTER_DEBUG
    Buffer fake_root_of_trust("000111222333444555666777888999000", 32);
    Buffer verified_boot_hash_none;
    if (!root_of_trust_set_) {
        /* Sets bootloader parameters to what is expected on a 'good' device,
         * will pass attestation CTS tests. FOR DEBUGGING ONLY.
         */
        SetBootParams(os_version, os_patchlevel, fake_root_of_trust,
                      KM_VERIFIED_BOOT_VERIFIED, true, verified_boot_hash_none);
    }
#endif

    return KM_ERROR_OK;
}

void TrustyKeymasterContext::GetSystemVersion(uint32_t* os_version,
                                              uint32_t* os_patchlevel) const {
    *os_version = boot_os_version_;
    *os_patchlevel = boot_os_patchlevel_;
}

const AttestationContext::VerifiedBootParams*
TrustyKeymasterContext::GetVerifiedBootParams(keymaster_error_t* error) const {
    VerifiedBootParams& vb_parms =
            const_cast<VerifiedBootParams&>(verified_boot_params_);

    vb_parms.verified_boot_key = {verified_boot_key_.begin(),
                                  verified_boot_key_.buffer_size()};
    vb_parms.verified_boot_hash = {verified_boot_hash_.begin(),
                                   verified_boot_hash_.buffer_size()};
    vb_parms.verified_boot_state = verified_boot_state_;
    vb_parms.device_locked = device_locked_;

    *error = KM_ERROR_OK;
    return &verified_boot_params_;
}

KeymasterKeyBlob TrustyKeymasterContext::GetAttestationKey(
        keymaster_algorithm_t algorithm,
        keymaster_error_t* error) const {
    AttestationKeySlot key_slot;

    switch (algorithm) {
    case KM_ALGORITHM_RSA:
        key_slot = AttestationKeySlot::kRsa;
        break;

    case KM_ALGORITHM_EC:
        key_slot = AttestationKeySlot::kEcdsa;
        break;

    default:
        *error = KM_ERROR_UNSUPPORTED_ALGORITHM;
        return {};
    }

    SecureStorageManager* ss_manager = SecureStorageManager::get_instance();
    if (ss_manager == nullptr) {
        LOG_E("Failed to open secure storage session.", 0);
        *error = KM_ERROR_SECURE_HW_COMMUNICATION_FAILED;
        return {};
    }
    auto result = ss_manager->ReadKeyFromStorage(key_slot, error);
#if KEYMASTER_SOFT_ATTESTATION_FALLBACK
    if (*error != KM_ERROR_OK) {
        LOG_I("Failed to read attestation key from RPMB, falling back to test key",
              0);
        auto key = getAttestationKey(algorithm, error);
        if (*error != KM_ERROR_OK) {
            LOG_D("Software attestation key missing: %d", *error);
            return {};
        }
        result = KeymasterKeyBlob(*key);
        if (!result.key_material)
            *error = KM_ERROR_MEMORY_ALLOCATION_FAILED;
    }
#endif
    return result;
}

CertificateChain TrustyKeymasterContext::GetAttestationChain(
        keymaster_algorithm_t algorithm,
        keymaster_error_t* error) const {
    AttestationKeySlot key_slot;
    switch (algorithm) {
    case KM_ALGORITHM_RSA:
        key_slot = AttestationKeySlot::kRsa;
        break;
    case KM_ALGORITHM_EC:
        key_slot = AttestationKeySlot::kEcdsa;
        break;
    default:
        *error = KM_ERROR_UNSUPPORTED_ALGORITHM;
        return {};
    }

    CertificateChain chain;
    SecureStorageManager* ss_manager = SecureStorageManager::get_instance();
    if (ss_manager == nullptr) {
        LOG_E("Failed to open secure storage session.", 0);
        *error = KM_ERROR_SECURE_HW_COMMUNICATION_FAILED;
    } else {
        *error = ss_manager->ReadCertChainFromStorage(key_slot, &chain);
    }
#if KEYMASTER_SOFT_ATTESTATION_FALLBACK
    if ((*error != KM_ERROR_OK) || (chain->entry_count == 0)) {
        LOG_I("Failed to read attestation chain from RPMB, falling back to test chain",
              0);
        chain = getAttestationChain(algorithm, error);
    }
#endif
    return chain;
}

CertificateChain TrustyKeymasterContext::GenerateAttestation(
        const Key& key,
        const AuthorizationSet& attest_params,
        UniquePtr<Key> attest_key,
        const KeymasterBlob& issuer_subject,
        keymaster_error_t* error) const {
    *error = KM_ERROR_OK;
    keymaster_algorithm_t key_algorithm;
    if (!key.authorizations().GetTagValue(TAG_ALGORITHM, &key_algorithm)) {
        *error = KM_ERROR_UNKNOWN_ERROR;
        return {};
    }

    if ((key_algorithm != KM_ALGORITHM_RSA &&
         key_algorithm != KM_ALGORITHM_EC)) {
        *error = KM_ERROR_INCOMPATIBLE_ALGORITHM;
        return {};
    }

    // We have established that the given key has the correct algorithm, and
    // because this is the TrustyKeymasterContext we can assume that the Key is
    // an AsymmetricKey. So we can downcast.
    const AsymmetricKey& asymmetric_key =
            static_cast<const AsymmetricKey&>(key);

    AttestKeyInfo attest_key_info(attest_key, &issuer_subject, error);
    if (*error != KM_ERROR_OK) {
        return {};
    }

    return generate_attestation(asymmetric_key, attest_params,
                                move(attest_key_info), *this, error);
}

CertificateChain TrustyKeymasterContext::GenerateSelfSignedCertificate(
        const Key& key,
        const AuthorizationSet& cert_params,
        bool fake_signature,
        keymaster_error_t* error) const {
    keymaster_algorithm_t key_algorithm;
    if (!key.authorizations().GetTagValue(TAG_ALGORITHM, &key_algorithm)) {
        *error = KM_ERROR_UNKNOWN_ERROR;
        return {};
    }

    if ((key_algorithm != KM_ALGORITHM_RSA &&
         key_algorithm != KM_ALGORITHM_EC)) {
        *error = KM_ERROR_INCOMPATIBLE_ALGORITHM;
        return {};
    }

    const AsymmetricKey& asymmetric_key =
            static_cast<const AsymmetricKey&>(key);

    return generate_self_signed_cert(asymmetric_key, cert_params,
                                     fake_signature, error);
}

keymaster_error_t TrustyKeymasterContext::SetBootParams(
        uint32_t /* os_version */,
        uint32_t /* os_patchlevel */,
        const Buffer& verified_boot_key,
        keymaster_verified_boot_t verified_boot_state,
        bool device_locked,
        const Buffer& verified_boot_hash) {
    if (root_of_trust_set_)
        return KM_ERROR_ROOT_OF_TRUST_ALREADY_SET;

    verified_boot_hash_.Reinitialize(verified_boot_hash);
    root_of_trust_set_ = true;
    verified_boot_state_ = verified_boot_state;
    device_locked_ = device_locked;
    verified_boot_key_.Reinitialize("", 0);

    // If the device is verified or self signed, load the key (if present)
    if ((verified_boot_state == KM_VERIFIED_BOOT_VERIFIED) ||
        (verified_boot_state == KM_VERIFIED_BOOT_SELF_SIGNED)) {
        if (verified_boot_key.buffer_size()) {
            verified_boot_key_.Reinitialize(verified_boot_key);
        } else {
            // If no boot key was passed, default to unverified/unlocked
            verified_boot_state_ = KM_VERIFIED_BOOT_UNVERIFIED;
            device_locked_ = false;
        }
    } else {
        // If the device image was not signed, it cannot be locked
        device_locked_ = false;
    }

    return KM_ERROR_OK;
}

// Mostly adapted from pure_soft_keymaster_context.cpp
keymaster_error_t TrustyKeymasterContext::UnwrapKey(
        const KeymasterKeyBlob& wrapped_key_blob,
        const KeymasterKeyBlob& wrapping_key_blob,
        const AuthorizationSet& wrapping_key_params,
        const KeymasterKeyBlob& masking_key,
        AuthorizationSet* wrapped_key_params,
        keymaster_key_format_t* wrapped_key_format,
        KeymasterKeyBlob* wrapped_key_material) const {
    LOG_D("UnwrapKey:0", 0);

    keymaster_error_t error = KM_ERROR_OK;

    if (wrapped_key_material == NULL) {
        return KM_ERROR_UNEXPECTED_NULL_POINTER;
    }

    LOG_D("UnwrapKey:1", 0);
    // Step 1 from IKeymasterDevice.hal file spec
    // Parse wrapping key
    UniquePtr<Key> wrapping_key;
    error = ParseKeyBlob(wrapping_key_blob, wrapping_key_params, &wrapping_key);
    if (error != KM_ERROR_OK) {
        LOG_E("Failed to parse wrapping key", 0);
        return error;
    }

    AuthProxy wrapping_key_auths(wrapping_key->hw_enforced(),
                                 wrapping_key->sw_enforced());

    // Check Wrapping Key Purpose
    if (!wrapping_key_auths.Contains(TAG_PURPOSE, KM_PURPOSE_WRAP)) {
        LOG_E("Wrapping key did not have KM_PURPOSE_WRAP", 0);
        return KM_ERROR_INCOMPATIBLE_PURPOSE;
    }

    // Check Padding mode is RSA_OAEP and digest is SHA_2_256 (spec mandated)
    if (!wrapping_key_auths.Contains(TAG_DIGEST, KM_DIGEST_SHA_2_256)) {
        LOG_E("Wrapping key lacks authorization for SHA2-256", 0);
        return KM_ERROR_INCOMPATIBLE_DIGEST;
    }
    if (!wrapping_key_auths.Contains(TAG_PADDING, KM_PAD_RSA_OAEP)) {
        LOG_E("Wrapping key lacks authorization for padding OAEP", 0);
        return KM_ERROR_INCOMPATIBLE_PADDING_MODE;
    }

    // Check that that was also the padding mode and digest specified
    if (!wrapping_key_params.Contains(TAG_DIGEST, KM_DIGEST_SHA_2_256)) {
        LOG_E("Wrapping key must use SHA2-256", 0);
        return KM_ERROR_INCOMPATIBLE_DIGEST;
    }
    if (!wrapping_key_params.Contains(TAG_PADDING, KM_PAD_RSA_OAEP)) {
        LOG_E("Wrapping key must use OAEP padding", 0);
        return KM_ERROR_INCOMPATIBLE_PADDING_MODE;
    }

    LOG_D("UnwrapKey:2", 0);
    // Step 2 from IKeymasterDevice.hal spec
    // Parse wrapped key
    KeymasterBlob iv;
    KeymasterKeyBlob transit_key;
    KeymasterKeyBlob secure_key;
    KeymasterBlob tag;
    KeymasterBlob wrapped_key_description;
    error = parse_wrapped_key(wrapped_key_blob, &iv, &transit_key, &secure_key,
                              &tag, wrapped_key_params, wrapped_key_format,
                              &wrapped_key_description);
    if (error != KM_ERROR_OK) {
        return error;
    }

    // Decrypt encryptedTransportKey (transit_key) with wrapping_key
    auto operation_factory = wrapping_key->key_factory()->GetOperationFactory(
            KM_PURPOSE_DECRYPT);
    if (operation_factory == NULL) {
        return KM_ERROR_UNKNOWN_ERROR;
    }

    AuthorizationSet out_params;
    OperationPtr operation(operation_factory->CreateOperation(
            move(*wrapping_key), wrapping_key_params, &error));
    if ((operation.get() == NULL) || (error != KM_ERROR_OK)) {
        return error;
    }

    error = operation->Begin(wrapping_key_params, &out_params);
    if (error != KM_ERROR_OK) {
        return error;
    }

    Buffer input;
    Buffer output;
    // Explicitly reinitialize rather than constructing in order to report
    // allocation failure.
    if (!input.Reinitialize(transit_key.key_material,
                            transit_key.key_material_size)) {
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;
    }

    error = operation->Finish(wrapping_key_params, input,
                              Buffer() /* signature */, &out_params, &output);
    if (error != KM_ERROR_OK) {
        return error;
    }

    KeymasterKeyBlob transport_key = {
            output.peek_read(),
            output.available_read(),
    };

    LOG_D("UnwrapKey:3", 0);
    // Step 3 of IKeymasterDevice.hal
    // XOR the transit key with the masking key
    if (transport_key.key_material_size != masking_key.key_material_size) {
        return KM_ERROR_INVALID_ARGUMENT;
    }
    for (size_t i = 0; i < transport_key.key_material_size; i++) {
        transport_key.writable_data()[i] ^= masking_key.key_material[i];
    }

    LOG_D("UnwrapKey:4", 0);
    // Step 4 of IKeymasterDevice.hal
    // transit_key_authorizations is defined by spec
    // TODO the mac len is NOT in the spec, but probably should be
    auto transport_key_authorizations =
            AuthorizationSetBuilder()
                    .AesEncryptionKey(256)
                    .Padding(KM_PAD_NONE)
                    .Authorization(TAG_BLOCK_MODE, KM_MODE_GCM)
                    .Authorization(TAG_NONCE, iv)
                    .Authorization(TAG_MIN_MAC_LENGTH, 128)
                    .build();
    auto validity = transport_key_authorizations.is_valid();
    if (validity != AuthorizationSet::Error::OK) {
        return TranslateAuthorizationSetError(validity);
    }

    // gcm_params is also defined by spec
    // TODO same problem with mac len not being specced
    auto gcm_params = AuthorizationSetBuilder()
                              .Padding(KM_PAD_NONE)
                              .Authorization(TAG_BLOCK_MODE, KM_MODE_GCM)
                              .Authorization(TAG_NONCE, iv)
                              .Authorization(TAG_MAC_LENGTH, 128)
                              .build();
    validity = gcm_params.is_valid();
    if (validity != AuthorizationSet::Error::OK) {
        return TranslateAuthorizationSetError(validity);
    }

    auto aes_factory = GetKeyFactory(KM_ALGORITHM_AES);
    if (aes_factory == NULL) {
        return KM_ERROR_UNKNOWN_ERROR;
    }

    UniquePtr<Key> aes_transport_key;
    error = aes_factory->LoadKey(move(transport_key), gcm_params,
                                 move(transport_key_authorizations),
                                 AuthorizationSet(), &aes_transport_key);
    if (error != KM_ERROR_OK) {
        return error;
    }

    auto aes_operation_factory =
            GetOperationFactory(KM_ALGORITHM_AES, KM_PURPOSE_DECRYPT);
    if (aes_operation_factory == NULL) {
        return KM_ERROR_UNKNOWN_ERROR;
    }

    OperationPtr aes_operation(aes_operation_factory->CreateOperation(
            move(*aes_transport_key), gcm_params, &error));
    if ((aes_operation.get() == NULL) || (error != KM_ERROR_OK)) {
        return error;
    }

    error = aes_operation->Begin(gcm_params, &out_params);
    if (error != KM_ERROR_OK) {
        return error;
    }

    size_t update_consumed = 0;
    AuthorizationSet update_outparams;

    Buffer encrypted_key;
    Buffer plaintext_key;

    // Separate initialization to catch memory errors
    size_t total_key_size = secure_key.key_material_size + tag.data_length;
    if (!plaintext_key.Reinitialize(total_key_size)) {
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;
    }
    if (!encrypted_key.Reinitialize(total_key_size)) {
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;
    }

    // Concatenate key data
    if (!encrypted_key.write(secure_key.key_material,
                             secure_key.key_material_size)) {
        return KM_ERROR_UNKNOWN_ERROR;
    }
    if (!encrypted_key.write(tag.data, tag.data_length)) {
        return KM_ERROR_UNKNOWN_ERROR;
    }

    auto update_params =
            AuthorizationSetBuilder()
                    .Authorization(TAG_ASSOCIATED_DATA,
                                   wrapped_key_description.data,
                                   wrapped_key_description.data_length)
                    .build();
    validity = update_params.is_valid();
    if (validity != AuthorizationSet::Error::OK) {
        return TranslateAuthorizationSetError(validity);
    }

    error = aes_operation->Update(update_params, encrypted_key,
                                  &update_outparams, &plaintext_key,
                                  &update_consumed);
    if (error != KM_ERROR_OK) {
        return error;
    }

    AuthorizationSet finish_params;
    AuthorizationSet finish_out_params;
    Buffer finish_input;
    error = aes_operation->Finish(finish_params, finish_input,
                                  Buffer() /* signature */, &finish_out_params,
                                  &plaintext_key);
    if (error != KM_ERROR_OK) {
        return error;
    }

    *wrapped_key_material = {plaintext_key.peek_read(),
                             plaintext_key.available_read()};

    if (!wrapped_key_material->key_material && plaintext_key.peek_read()) {
        return KM_ERROR_MEMORY_ALLOCATION_FAILED;
    }

    LOG_D("UnwrapKey:Done", 0);
    return error;
}

}  // namespace keymaster