//
// Copyright (C) 2014 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#include "trunks/hmac_authorization_delegate.h"
#include <base/logging.h>
#include <base/stl_util.h>
#include <crypto/secure_util.h>
#include <openssl/aes.h>
#include <openssl/hmac.h>
#include <openssl/rand.h>
namespace trunks {
namespace {
const uint32_t kDigestBits = 256;
const uint16_t kNonceMinSize = 16;
const uint16_t kNonceMaxSize = 32;
const uint8_t kDecryptSession = 1 << 5;
const uint8_t kEncryptSession = 1 << 6;
const uint8_t kLabelSize = 4;
const size_t kAesIVSize = 16;
const uint32_t kTpmBufferSize = 4096;
} // namespace
HmacAuthorizationDelegate::HmacAuthorizationDelegate()
: session_handle_(0),
is_parameter_encryption_enabled_(false),
nonce_generated_(false),
future_authorization_value_set_(false),
use_entity_authorization_for_encryption_only_(false) {
tpm_nonce_.size = 0;
caller_nonce_.size = 0;
}
HmacAuthorizationDelegate::~HmacAuthorizationDelegate() {}
bool HmacAuthorizationDelegate::GetCommandAuthorization(
const std::string& command_hash,
bool is_command_parameter_encryption_possible,
bool is_response_parameter_encryption_possible,
std::string* authorization) {
if (!session_handle_) {
authorization->clear();
LOG(ERROR) << "Delegate being used before Initialization,";
return false;
}
TPMS_AUTH_COMMAND auth;
auth.session_handle = session_handle_;
if (!nonce_generated_) {
RegenerateCallerNonce();
}
auth.nonce = caller_nonce_;
auth.session_attributes = kContinueSession;
if (is_parameter_encryption_enabled_) {
if (is_command_parameter_encryption_possible) {
auth.session_attributes |= kDecryptSession;
}
if (is_response_parameter_encryption_possible) {
auth.session_attributes |= kEncryptSession;
}
}
// We reset the |nonce_generated| flag in preperation of the next command.
nonce_generated_ = false;
std::string attributes_bytes;
CHECK_EQ(Serialize_TPMA_SESSION(auth.session_attributes, &attributes_bytes),
TPM_RC_SUCCESS)
<< "Error serializing session attributes.";
std::string hmac_data;
std::string hmac_key;
if (!use_entity_authorization_for_encryption_only_) {
hmac_key = session_key_ + entity_authorization_value_;
} else {
hmac_key = session_key_;
}
hmac_data.append(command_hash);
hmac_data.append(reinterpret_cast<const char*>(caller_nonce_.buffer),
caller_nonce_.size);
hmac_data.append(reinterpret_cast<const char*>(tpm_nonce_.buffer),
tpm_nonce_.size);
hmac_data.append(attributes_bytes);
std::string digest = HmacSha256(hmac_key, hmac_data);
auth.hmac = Make_TPM2B_DIGEST(digest);
TPM_RC serialize_error = Serialize_TPMS_AUTH_COMMAND(auth, authorization);
if (serialize_error != TPM_RC_SUCCESS) {
LOG(ERROR) << "Could not serialize command auth.";
return false;
}
return true;
}
bool HmacAuthorizationDelegate::CheckResponseAuthorization(
const std::string& response_hash,
const std::string& authorization) {
if (!session_handle_) {
return false;
}
TPMS_AUTH_RESPONSE auth_response;
std::string mutable_auth_string(authorization);
TPM_RC parse_error;
parse_error =
Parse_TPMS_AUTH_RESPONSE(&mutable_auth_string, &auth_response, nullptr);
if (parse_error != TPM_RC_SUCCESS) {
LOG(ERROR) << "Could not parse authorization response.";
return false;
}
if (auth_response.hmac.size != kHashDigestSize) {
LOG(ERROR) << "TPM auth hmac was incorrect size.";
return false;
}
if (auth_response.nonce.size < kNonceMinSize ||
auth_response.nonce.size > kNonceMaxSize) {
LOG(ERROR) << "TPM_nonce is not the correct length.";
return false;
}
tpm_nonce_ = auth_response.nonce;
std::string attributes_bytes;
CHECK_EQ(Serialize_TPMA_SESSION(auth_response.session_attributes,
&attributes_bytes),
TPM_RC_SUCCESS)
<< "Error serializing session attributes.";
std::string hmac_data;
std::string hmac_key;
if (!use_entity_authorization_for_encryption_only_) {
// In a special case with TPM2_HierarchyChangeAuth, we need to use the
// auth_value that was set.
if (future_authorization_value_set_) {
hmac_key = session_key_ + future_authorization_value_;
future_authorization_value_set_ = false;
} else {
hmac_key = session_key_ + entity_authorization_value_;
}
} else {
hmac_key = session_key_;
}
hmac_data.append(response_hash);
hmac_data.append(reinterpret_cast<const char*>(tpm_nonce_.buffer),
tpm_nonce_.size);
hmac_data.append(reinterpret_cast<const char*>(caller_nonce_.buffer),
caller_nonce_.size);
hmac_data.append(attributes_bytes);
std::string digest = HmacSha256(hmac_key, hmac_data);
CHECK_EQ(digest.size(), auth_response.hmac.size);
if (!crypto::SecureMemEqual(digest.data(), auth_response.hmac.buffer,
digest.size())) {
LOG(ERROR) << "Authorization response hash did not match expected value.";
return false;
}
return true;
}
bool HmacAuthorizationDelegate::EncryptCommandParameter(
std::string* parameter) {
CHECK(parameter);
if (!session_handle_) {
LOG(ERROR) << __func__ << ": Invalid session handle.";
return false;
}
if (!is_parameter_encryption_enabled_) {
// No parameter encryption enabled.
return true;
}
if (parameter->size() > kTpmBufferSize) {
LOG(ERROR) << "Parameter size is too large for TPM decryption.";
return false;
}
RegenerateCallerNonce();
nonce_generated_ = true;
AesOperation(parameter, caller_nonce_, tpm_nonce_, AES_ENCRYPT);
return true;
}
bool HmacAuthorizationDelegate::DecryptResponseParameter(
std::string* parameter) {
CHECK(parameter);
if (!session_handle_) {
LOG(ERROR) << __func__ << ": Invalid session handle.";
return false;
}
if (!is_parameter_encryption_enabled_) {
// No parameter decryption enabled.
return true;
}
if (parameter->size() > kTpmBufferSize) {
LOG(ERROR) << "Parameter size is too large for TPM encryption.";
return false;
}
AesOperation(parameter, tpm_nonce_, caller_nonce_, AES_DECRYPT);
return true;
}
bool HmacAuthorizationDelegate::InitSession(TPM_HANDLE session_handle,
const TPM2B_NONCE& tpm_nonce,
const TPM2B_NONCE& caller_nonce,
const std::string& salt,
const std::string& bind_auth_value,
bool enable_parameter_encryption) {
session_handle_ = session_handle;
if (caller_nonce.size < kNonceMinSize || caller_nonce.size > kNonceMaxSize ||
tpm_nonce.size < kNonceMinSize || tpm_nonce.size > kNonceMaxSize) {
LOG(INFO) << "Session Nonces have to be between 16 and 32 bytes long.";
return false;
}
tpm_nonce_ = tpm_nonce;
caller_nonce_ = caller_nonce;
std::string session_key_label("ATH", kLabelSize);
is_parameter_encryption_enabled_ = enable_parameter_encryption;
if (salt.length() == 0 && bind_auth_value.length() == 0) {
// SessionKey is set to the empty string for unsalted and
// unbound sessions.
session_key_ = std::string();
} else {
session_key_ = CreateKey(bind_auth_value + salt, session_key_label,
tpm_nonce_, caller_nonce_);
}
return true;
}
void HmacAuthorizationDelegate::set_future_authorization_value(
const std::string& auth_value) {
future_authorization_value_ = auth_value;
future_authorization_value_set_ = true;
}
std::string HmacAuthorizationDelegate::CreateKey(
const std::string& hmac_key,
const std::string& label,
const TPM2B_NONCE& nonce_newer,
const TPM2B_NONCE& nonce_older) {
std::string counter;
std::string digest_size_bits;
if (Serialize_uint32_t(1, &counter) != TPM_RC_SUCCESS ||
Serialize_uint32_t(kDigestBits, &digest_size_bits) != TPM_RC_SUCCESS) {
LOG(ERROR) << "Error serializing uint32_t during session key generation.";
return std::string();
}
CHECK_EQ(counter.size(), sizeof(uint32_t));
CHECK_EQ(digest_size_bits.size(), sizeof(uint32_t));
CHECK_EQ(label.size(), kLabelSize);
std::string data;
data.append(counter);
data.append(label);
data.append(reinterpret_cast<const char*>(nonce_newer.buffer),
nonce_newer.size);
data.append(reinterpret_cast<const char*>(nonce_older.buffer),
nonce_older.size);
data.append(digest_size_bits);
std::string key = HmacSha256(hmac_key, data);
return key;
}
std::string HmacAuthorizationDelegate::HmacSha256(const std::string& key,
const std::string& data) {
unsigned char digest[EVP_MAX_MD_SIZE];
unsigned int digest_length;
HMAC(EVP_sha256(), key.data(), key.size(),
reinterpret_cast<const unsigned char*>(data.data()), data.size(), digest,
&digest_length);
CHECK_EQ(digest_length, kHashDigestSize);
return std::string(reinterpret_cast<char*>(digest), digest_length);
}
void HmacAuthorizationDelegate::AesOperation(std::string* parameter,
const TPM2B_NONCE& nonce_newer,
const TPM2B_NONCE& nonce_older,
int operation_type) {
std::string label("CFB", kLabelSize);
std::string compound_key =
CreateKey(session_key_ + entity_authorization_value_, label, nonce_newer,
nonce_older);
CHECK_EQ(compound_key.size(), kAesKeySize + kAesIVSize);
unsigned char aes_key[kAesKeySize];
unsigned char aes_iv[kAesIVSize];
memcpy(aes_key, &compound_key[0], kAesKeySize);
memcpy(aes_iv, &compound_key[kAesKeySize], kAesIVSize);
AES_KEY key;
int iv_offset = 0;
AES_set_encrypt_key(aes_key, kAesKeySize * 8, &key);
unsigned char decrypted[kTpmBufferSize];
AES_cfb128_encrypt(reinterpret_cast<const unsigned char*>(parameter->data()),
decrypted, parameter->size(), &key, aes_iv, &iv_offset,
operation_type);
memcpy(base::string_as_array(parameter), decrypted, parameter->size());
}
void HmacAuthorizationDelegate::RegenerateCallerNonce() {
CHECK(session_handle_);
// RAND_bytes takes a signed number, but since nonce_size is guaranteed to be
// less than 32 bytes and greater than 16 we dont have to worry about it.
CHECK_EQ(RAND_bytes(caller_nonce_.buffer, caller_nonce_.size), 1)
<< "Error regnerating a cryptographically random nonce.";
}
} // namespace trunks