chaps/tpm2_utility_impl.cc

// Copyright 2015 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <utility>

#include "chaps/chaps_utility.h"
#include "chaps/tpm2_utility_impl.h"

#include <base/bind.h>
#include <base/files/file_path.h>
#include <base/files/file_util.h>
#include <base/location.h>
#include <base/logging.h>
#include <base/macros.h>
#include <base/memory/ref_counted.h>
#include <base/sha1.h>
#include <base/stl_util.h>
#include <crypto/scoped_openssl_types.h>
#include <openssl/rsa.h>
#include <trunks/background_command_transceiver.h>
#include <trunks/command_transceiver.h>
#include <trunks/error_codes.h>
#include <trunks/tpm_generated.h>
#include <trunks/tpm_state.h>
#include <trunks/trunks_dbus_proxy.h>
#include <trunks/trunks_factory_impl.h>

using base::AutoLock;
using brillo::SecureBlob;
using std::map;
using std::set;
using trunks::kRSAStorageRootKey;
using trunks::TPM_RC;
using trunks::TPM_RC_SUCCESS;
using trunks::TrunksFactory;

namespace {

const struct {
  trunks::TPM_ALG_ID id;
  chaps::DigestAlgorithm alg;
} kSupportedDigestAlgorithms[] = {
  { trunks::TPM_ALG_SHA1,   chaps::DigestAlgorithm::SHA1 },
  { trunks::TPM_ALG_SHA256, chaps::DigestAlgorithm::SHA256 },
  { trunks::TPM_ALG_SHA384, chaps::DigestAlgorithm::SHA384 },
  { trunks::TPM_ALG_SHA512, chaps::DigestAlgorithm::SHA512 },
};

// Extract the algorithm ID and the digest from PKCS1-v1_5 DigestInfo.
// See RFC-3447, section 9.2.
void ParseDigestInfo(const std::string& digest_info,
                     std::string* digest,
                     trunks::TPM_ALG_ID* digest_alg) {
  for (size_t i = 0; i < arraysize(kSupportedDigestAlgorithms); ++i) {
    std::string encoding =
      GetDigestAlgorithmEncoding(kSupportedDigestAlgorithms[i].alg);
    if (!digest_info.compare(0, encoding.size(), encoding)) {
      *digest = digest_info.substr(encoding.size());
      *digest_alg = kSupportedDigestAlgorithms[i].id;
      return;
    }
  }
  // Unknown algorithm - use "padding-only" signing scheme.
  *digest = digest_info;
  *digest_alg = trunks::TPM_ALG_NULL;
}

uint32_t GetIntegerExponent(const std::string& public_exponent) {
  uint32_t exponent = 0;
  for (size_t i = 0; i < public_exponent.size(); i++) {
    exponent = exponent << 8;
    exponent += public_exponent[i];
  }
  return exponent;
}

bool AddPKCS1Padding(const std::string& input,
                     size_t size,
                     std::string* result) {
  if (input.size() + 11 > size) {
    LOG(ERROR) << "Error adding PKCS1 padding: message too long: "
               << input.size() << " (target size " << size << ")";
    return false;
  }
  result->assign("\x00\x01", 2);
  result->append(size - input.size() - 3, '\xff');
  result->append("\x00", 1);
  result->append(input);
  return true;
}

void InitTransceiver(trunks::CommandTransceiver* transceiver) {
  if (!transceiver->Init()) {
    LOG(ERROR) << "Error initializing transceiver.";
  }
}

void TermTransceiver(std::unique_ptr<trunks::CommandTransceiver> transceiver) {
  transceiver.reset();
}

}  // namespace

namespace chaps {

class ScopedSession {
 public:
#ifndef CHAPS_TPM2_USE_PER_OP_SESSIONS
  ScopedSession(trunks::TrunksFactory* factory,
      std::unique_ptr<trunks::HmacSession> *session) {}
#else
  ScopedSession(trunks::TrunksFactory* factory,
      std::unique_ptr<trunks::HmacSession> *session) {
    target_session_ = session;
    if (*target_session_) {
      LOG(ERROR) << "Concurrent sessions";
    }
    std::unique_ptr<trunks::HmacSession> new_session =
      factory->GetHmacSession();
    TPM_RC result =
      new_session->StartUnboundSession(false /* disable encryption */);
    if (result != TPM_RC_SUCCESS) {
      LOG(ERROR) << "Error starting an AuthorizationSession: "
                 << trunks::GetErrorString(result);
      *target_session_ = nullptr;
    } else {
      *target_session_ = std::move(new_session);
    }
  }
  ~ScopedSession() {
    *target_session_ = nullptr;
  }

 private:
  std::unique_ptr<trunks::HmacSession> *target_session_;
#endif
};

TPM2UtilityImpl::TPM2UtilityImpl()
    : default_factory_(
        new trunks::TrunksFactoryImpl()),
      factory_(default_factory_.get()) {
  if (!default_factory_->Initialize()) {
    LOG(ERROR) << "Unable to initialize trunks.";
    return;
  }
#ifndef CHAPS_TPM2_USE_PER_OP_SESSIONS
  session_ = factory_->GetHmacSession();
#endif
  trunks_tpm_utility_ = factory_->GetTpmUtility();
}

TPM2UtilityImpl::TPM2UtilityImpl(
    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner)
        : task_runner_(task_runner),
          default_trunks_proxy_(new trunks::TrunksDBusProxy) {
  task_runner->PostNonNestableTask(
      FROM_HERE,
      base::Bind(&InitTransceiver,
                 base::Unretained(default_trunks_proxy_.get())));
  // We stitch the transceivers together. The call chain is:
  // ChapsTPMUtility --> TrunksFactory --> BackgroundCommandTransceiver -->
  // TrunksProxy
  default_background_transceiver_.reset(
      new trunks::BackgroundCommandTransceiver(
          default_trunks_proxy_.get(),
          task_runner));
  default_factory_.reset(
      new trunks::TrunksFactoryImpl(default_background_transceiver_.get()));
  CHECK(default_factory_->Initialize());
  factory_ = default_factory_.get();
#ifndef CHAPS_TPM2_USE_PER_OP_SESSIONS
  session_ = factory_->GetHmacSession();
#endif
  trunks_tpm_utility_ = factory_->GetTpmUtility();
}

TPM2UtilityImpl::TPM2UtilityImpl(TrunksFactory* factory)
    : factory_(factory),
#ifndef CHAPS_TPM2_USE_PER_OP_SESSIONS
      session_(factory_->GetHmacSession()),
#endif
      trunks_tpm_utility_(factory_->GetTpmUtility()) {}

TPM2UtilityImpl::~TPM2UtilityImpl() {
  for (const auto& it : slot_handles_) {
    set<int> slot_handles = it.second;
    for (const auto& it2 : slot_handles) {
      if (factory_->GetTpm()->FlushContextSync(it2, NULL) != TPM_RC_SUCCESS) {
        LOG(WARNING) << "Error flushing handle: " << it2;
      }
    }
  }

  // If we have a task runner, then that was the task runner used to initialize
  // the |default_trunks_proxy_|. Destroy the proxy on that task runner to
  // satisfy threading restrictions.
  if (task_runner_) {
    default_factory_.reset();
    default_background_transceiver_.reset();
    // TODO(ejcaruso): replace with DeleteSoon when libchrome has the unique_ptr
    // specialization after the uprev
    task_runner_->PostNonNestableTask(
        FROM_HERE,
        base::Bind(&TermTransceiver,
                   base::Passed(&default_trunks_proxy_)));
  }
}

bool TPM2UtilityImpl::Init() {
  AutoLock lock(lock_);
  std::unique_ptr<trunks::TpmState> tpm_state = factory_->GetTpmState();
  TPM_RC result;
  result = tpm_state->Initialize();
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error getting TPM state information: "
               << trunks::GetErrorString(result);
    return false;
  }
  // Check if firmware initialized the platform hierarchy.
  if (tpm_state->IsPlatformHierarchyEnabled()) {
    LOG(ERROR) << "Platform initialization not complete.";
    return false;
  }
  // Check if ownership is taken. If not, TPMUtility initialization fails.
  if (!tpm_state->IsOwnerPasswordSet() ||
      !tpm_state->IsEndorsementPasswordSet() ||
      !tpm_state->IsLockoutPasswordSet()) {
    LOG(ERROR) << "TPM2Utility cannot be ready if the TPM is not owned.";
    return false;
  }
#ifndef CHAPS_TPM2_USE_PER_OP_SESSIONS
  result = session_->StartUnboundSession(true /* enable encryption */);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error starting an AuthorizationSession: "
               << trunks::GetErrorString(result);
    return false;
  }
#endif
  is_initialized_ = true;
  return true;
}

bool TPM2UtilityImpl::IsTPMAvailable() {
  AutoLock lock(lock_);
  if (is_enabled_ready_) {
    return is_enabled_;
  }
  // If the TPM works, it is available.
  if (is_initialized_) {
    is_enabled_ready_ = true;
    is_enabled_ = true;
    return true;
  }
  std::unique_ptr<trunks::TpmState> tpm_state = factory_->GetTpmState();
  TPM_RC result = tpm_state->Initialize();
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error getting TPM state information: "
               << trunks::GetErrorString(result);
    return false;
  }
  is_enabled_ = tpm_state->IsEnabled();
  is_enabled_ready_ = true;
  return is_enabled_;
}

bool TPM2UtilityImpl::Authenticate(int slot_id,
                                   const SecureBlob& auth_data,
                                   const std::string& auth_key_blob,
                                   const std::string& encrypted_master_key,
                                   SecureBlob* master_key) {
  CHECK(master_key);
  AutoLock lock(lock_);
  int key_handle = 0;
  if (!LoadKeyWithParentInternal(slot_id, auth_key_blob, auth_data,
                                 kRSAStorageRootKey, &key_handle)) {
    return false;
  }
  std::string master_key_str;
  if (!UnbindInternal(key_handle, encrypted_master_key, &master_key_str)) {
    return false;
  }
  *master_key = SecureBlob(master_key_str);
  master_key_str.clear();
  return true;
}

bool TPM2UtilityImpl::ChangeAuthData(int slot_id,
                                     const SecureBlob& old_auth_data,
                                     const SecureBlob& new_auth_data,
                                     const std::string& old_auth_key_blob,
                                     std::string* new_auth_key_blob) {
  AutoLock lock(lock_);
  int key_handle;
  if (new_auth_data.size() > SHA256_DIGEST_SIZE) {
    LOG(ERROR) << "Authorization cannot be larger than SHA256 Digest size.";
    return false;
  }
  if (!LoadKeyWithParentInternal(slot_id, old_auth_key_blob, old_auth_data,
                                 kRSAStorageRootKey, &key_handle)) {
    LOG(ERROR) << "Error loading key under old authorization data.";
    return false;
  }
  ScopedSession session_scope(factory_, &session_);
  if (!session_) {
    return false;
  }
  session_->SetEntityAuthorizationValue(old_auth_data.to_string());
  TPM_RC result = trunks_tpm_utility_->ChangeKeyAuthorizationData(
      key_handle,
      new_auth_data.to_string(),
      session_->GetDelegate(),
      new_auth_key_blob);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error changing authorization data: "
               << trunks::GetErrorString(result);
    return false;
  }
  result = factory_->GetTpm()->FlushContextSync(key_handle, NULL);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error unloading key under old authorization: "
               << trunks::GetErrorString(result);
    return false;
  }
  slot_handles_[slot_id].erase(key_handle);
  FlushHandle(key_handle);
  return true;
}

bool TPM2UtilityImpl::GenerateRandom(int num_bytes, std::string* random_data) {
  AutoLock lock(lock_);
  TPM_RC result = trunks_tpm_utility_->GenerateRandom(num_bytes,
                                                      nullptr,
                                                      random_data);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error generating random data from the TPM: "
               << trunks::GetErrorString(result);
    return false;
  }
  return true;
}

bool TPM2UtilityImpl::StirRandom(const std::string& entropy_data) {
  AutoLock lock(lock_);
  TPM_RC result = trunks_tpm_utility_->StirRandom(entropy_data, nullptr);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error seeding TPM random number generator: "
               << trunks::GetErrorString(result);
    return false;
  }
  return true;
}

bool TPM2UtilityImpl::GenerateKey(int slot,
                                  int modulus_bits,
                                  const std::string& public_exponent,
                                  const SecureBlob& auth_data,
                                  std::string* key_blob,
                                  int* key_handle) {
  AutoLock lock(lock_);
  if (public_exponent.size() > 4) {
    LOG(ERROR) << "Incorrectly formatted public_exponent.";
    return false;
  }
  if (auth_data.size() > SHA256_DIGEST_SIZE) {
    LOG(ERROR) << "Authorization cannot be larger than SHA256 Digest size.";
    return false;
  }
  if (modulus_bits < static_cast<int>(kMinModulusSize)) {
    LOG(ERROR) << "Minimum modulus size is: " << kMinModulusSize;
  }
  ScopedSession session_scope(factory_, &session_);
  if (!session_) {
    return false;
  }
  session_->SetEntityAuthorizationValue("");  // SRK Authorization Value.
  TPM_RC result = trunks_tpm_utility_->CreateRSAKeyPair(
      trunks::TpmUtility::AsymmetricKeyUsage::kDecryptAndSignKey,
      modulus_bits,
      GetIntegerExponent(public_exponent),
      auth_data.to_string(),
      "",  // Policy Digest
      false,  // use_only_policy_authorization
      trunks::kNoCreationPCR,
      session_->GetDelegate(),
      key_blob,
      nullptr);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error creating RSA key pair: "
               << trunks::GetErrorString(result);
    return false;
  }
  if (!LoadKeyWithParentInternal(slot, *key_blob, auth_data,
                                 kRSAStorageRootKey, key_handle)) {
    return false;
  }
  return true;
}

bool TPM2UtilityImpl::GetPublicKey(int key_handle,
                                   std::string* public_exponent,
                                   std::string* modulus) {
  AutoLock lock(lock_);
  trunks::TPMT_PUBLIC public_data;
  TPM_RC result = trunks_tpm_utility_->GetKeyPublicArea(key_handle,
                                                        &public_data);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error getting key public data: " << result;
    return false;
  }
  public_exponent->clear();
  result = trunks::Serialize_UINT32(public_data.parameters.rsa_detail.exponent,
                                    public_exponent);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error serializing public exponent: " << result;
    return false;
  }
  modulus->assign(StringFrom_TPM2B_PUBLIC_KEY_RSA(public_data.unique.rsa));
  return true;
}

bool TPM2UtilityImpl::WrapKey(int slot,
                              const std::string& public_exponent,
                              const std::string& modulus,
                              const std::string& prime_factor,
                              const SecureBlob& auth_data,
                              std::string* key_blob,
                              int* key_handle) {
  AutoLock lock(lock_);
  if (public_exponent.size() > 4) {
    LOG(ERROR) << "Incorrectly formatted public_exponent.";
    return false;
  }
  if (auth_data.size() > SHA256_DIGEST_SIZE) {
    LOG(ERROR) << "Authorization cannot be larger than SHA256 Digest size.";
    return false;
  }
  if (modulus.size() < kMinModulusSize) {
    LOG(ERROR) << "Minimum modulus size is: " << kMinModulusSize;
    return false;
  }
  ScopedSession session_scope(factory_, &session_);
  if (!session_) {
    return false;
  }
  session_->SetEntityAuthorizationValue("");  // SRK Authorization Value.
  TPM_RC result = trunks_tpm_utility_->ImportRSAKey(
      trunks::TpmUtility::AsymmetricKeyUsage::kDecryptAndSignKey,
      modulus,
      GetIntegerExponent(public_exponent),
      prime_factor,
      auth_data.to_string(),
      session_->GetDelegate(),
      key_blob);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error importing RSA key to TPM: "
               << trunks::GetErrorString(result);
    return false;
  }
  if (!LoadKeyWithParentInternal(slot, *key_blob, auth_data,
                                 kRSAStorageRootKey, key_handle)) {
    return false;
  }
  return true;
}

bool TPM2UtilityImpl::LoadKey(int slot,
                              const std::string& key_blob,
                              const SecureBlob& auth_data,
                              int* key_handle) {
  AutoLock lock(lock_);
  return LoadKeyWithParentInternal(slot,
                                   key_blob,
                                   auth_data,
                                   kRSAStorageRootKey,
                                   key_handle);
}

bool TPM2UtilityImpl::LoadKeyWithParent(int slot,
                                        const std::string& key_blob,
                                        const SecureBlob& auth_data,
                                        int parent_key_handle,
                                        int* key_handle) {
  AutoLock lock(lock_);
  return LoadKeyWithParentInternal(slot,
                                   key_blob,
                                   auth_data,
                                   parent_key_handle,
                                   key_handle);
}

void TPM2UtilityImpl::UnloadKeysForSlot(int slot) {
  AutoLock Lock(lock_);
  for (const auto& it : slot_handles_[slot]) {
    if (factory_->GetTpm()->FlushContextSync(it, NULL) != TPM_RC_SUCCESS) {
      LOG(WARNING) << "Error flushing handle: " << it;
    }
    FlushHandle(it);
  }
  slot_handles_.erase(slot);
}

bool TPM2UtilityImpl::Bind(int key_handle,
                           const std::string& input,
                           std::string* output) {
  CHECK(output);
  std::string modulus;
  std::string exponent;
  if (!GetPublicKey(key_handle, &exponent, &modulus)) {
    return false;
  }
  if (input.size() > modulus.size() - 11) {
    LOG(ERROR) << "Encryption plaintext is longer than RSA modulus.";
    return false;
  }
  crypto::ScopedRSA rsa(RSA_new());
  rsa.get()->n = BN_bin2bn(
      reinterpret_cast<const unsigned char*>(modulus.data()),
      modulus.size(),
      nullptr);
  rsa.get()->e = BN_bin2bn(
      reinterpret_cast<const unsigned char*>(exponent.data()),
      exponent.size(),
      nullptr);
  // RSA encrypt output should be size of the modulus.
  output->resize(modulus.size());
  int rsa_result = RSA_public_encrypt(
      input.size(),
      reinterpret_cast<const unsigned char*>(input.data()),
      reinterpret_cast<unsigned char*>(string_as_array(output)),
      rsa.get(),
      RSA_PKCS1_PADDING);
  if (rsa_result == -1) {
    LOG(ERROR) << "Error performing RSA_public_encrypt.";
    return false;
  }
  return true;
}

bool TPM2UtilityImpl::Unbind(int key_handle,
                             const std::string& input,
                             std::string* output) {
  AutoLock lock(lock_);
  return UnbindInternal(key_handle, input, output);
}

bool TPM2UtilityImpl::Sign(int key_handle,
                           const std::string& input,
                           std::string* signature) {
  AutoLock Lock(lock_);
  std::string auth_data = handle_auth_data_[key_handle].to_string();
  ScopedSession session_scope(factory_, &session_);
  if (!session_) {
    return false;
  }
  session_->SetEntityAuthorizationValue(auth_data);
  trunks::TPMT_PUBLIC public_area;
  TPM_RC result = trunks_tpm_utility_->GetKeyPublicArea(key_handle,
                                                        &public_area);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error getting key public data: "
               << trunks::GetErrorString(result);
    return false;
  }
  // If decryption is allowed for the key, do padding in software (the
  // session layer already prepared the DigestInfo by prepending the algorithm
  // ID) and perform raw RSA on TPM by sending Decrypt command with NULL scheme.
  // Otherwise, strip the algorithm ID already prepended by the session level,
  // send Sign command to the TPM with the original unencoded digest, and let
  // TPM handle padding and encoding on its side.
  // This is done to work with TPMs that don't support all required hashing
  // algorithms, and for which the Decrypt attribute is set for signing keys.
  if (public_area.object_attributes & trunks::kDecrypt) {
    std::string padded_input;
    if (!AddPKCS1Padding(input, public_area.unique.rsa.size, &padded_input)) {
      return false;
    }
    result = trunks_tpm_utility_->AsymmetricDecrypt(key_handle,
                                                    trunks::TPM_ALG_NULL,
                                                    trunks::TPM_ALG_NULL,
                                                    padded_input,
                                                    session_->GetDelegate(),
                                                    signature);
  } else {
    std::string digest;
    trunks::TPM_ALG_ID digest_alg;
    ParseDigestInfo(input, &digest, &digest_alg);
    result = trunks_tpm_utility_->Sign(key_handle,
                                       trunks::TPM_ALG_RSASSA,
                                       digest_alg,
                                       digest,
                                       false /* don't generate hash */,
                                       session_->GetDelegate(),
                                       signature);
  }
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error performing sign operation: "
               << trunks::GetErrorString(result);
    return false;
  }
  return true;
}

bool TPM2UtilityImpl::Verify(int key_handle,
                             const std::string& input,
                             const std::string& signature) {
  std::string digest = base::SHA1HashString(input);
  crypto::ScopedRSA rsa(RSA_new());
  std::string modulus;
  std::string exponent;
  if (!GetPublicKey(key_handle, &exponent, &modulus)) {
    return false;
  }
  rsa.get()->n = BN_bin2bn(
      reinterpret_cast<const unsigned char*>(modulus.data()),
      modulus.size(),
      nullptr);
  rsa.get()->e = BN_bin2bn(
      reinterpret_cast<const unsigned char*>(exponent.data()),
      exponent.size(),
      nullptr);
  if (RSA_verify(NID_sha1,
                 reinterpret_cast<const unsigned char*>(digest.data()),
                 digest.size(),
                 reinterpret_cast<const unsigned char*>(signature.data()),
                 signature.size(),
                 rsa.get()) != 1) {
    LOG(ERROR) << "Signature was incorrect.";
    return false;
  }
  return true;
}

bool TPM2UtilityImpl::IsSRKReady() {
  return IsTPMAvailable() && Init();
}

bool TPM2UtilityImpl::LoadKeyWithParentInternal(int slot,
                                                const std::string& key_blob,
                                                const SecureBlob& auth_data,
                                                int parent_key_handle,
                                                int* key_handle) {
  CHECK_EQ(parent_key_handle, static_cast<int>(kRSAStorageRootKey))
      << "Chaps with TPM2.0 only loads keys under the RSA SRK.";
  if (auth_data.size() > SHA256_DIGEST_SIZE) {
    LOG(ERROR) << "Authorization cannot be larger than SHA256 Digest size.";
    return false;
  }
  ScopedSession session_scope(factory_, &session_);
  if (!session_) {
    return false;
  }
  session_->SetEntityAuthorizationValue("");  // SRK Authorization Value.
  TPM_RC result = trunks_tpm_utility_->LoadKey(
      key_blob,
      session_->GetDelegate(),
      reinterpret_cast<trunks::TPM_HANDLE*>(key_handle));
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error loading key into TPM: "
               << trunks::GetErrorString(result);
    return false;
  }
  std::string key_name;
  result = trunks_tpm_utility_->GetKeyName(*key_handle, &key_name);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error getting key name: " << trunks::GetErrorString(result);
    return false;
  }
  handle_auth_data_[*key_handle] = auth_data;
  handle_name_[*key_handle] = key_name;
  slot_handles_[slot].insert(*key_handle);
  return true;
}

bool TPM2UtilityImpl::UnbindInternal(int key_handle,
                                     const std::string& input,
                                     std::string* output) {
  trunks::TPMT_PUBLIC public_data;
  TPM_RC result = trunks_tpm_utility_->GetKeyPublicArea(key_handle,
                                                        &public_data);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error getting key public data: " << result;
    return false;
  }
  if (input.size() > public_data.unique.rsa.size) {
    LOG(ERROR) << "RSA decrypt ciphertext is larger than modulus.";
    return false;
  }
  std::string auth_data = handle_auth_data_[key_handle].to_string();
  ScopedSession session_scope(factory_, &session_);
  if (!session_) {
    return false;
  }
  session_->SetEntityAuthorizationValue(auth_data);
  result = trunks_tpm_utility_->AsymmetricDecrypt(key_handle,
                                                  trunks::TPM_ALG_RSAES,
                                                  trunks::TPM_ALG_SHA1,
                                                  input,
                                                  session_->GetDelegate(),
                                                  output);
  if (result != TPM_RC_SUCCESS) {
    LOG(ERROR) << "Error performing unbind operation: "
               << trunks::GetErrorString(result);
    return false;
  }
  return true;
}

void TPM2UtilityImpl::FlushHandle(int key_handle) {
  handle_auth_data_.erase(key_handle);
  handle_name_.erase(key_handle);
}

}  // namespace chaps