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phab/src/applications/files/format/PhabricatorFileAES256StorageFormat.php
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PhabricatorFileAES256StorageFormat.php
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<?php
/**
* At-rest encryption format using AES256 CBC.
*/
final class PhabricatorFileAES256StorageFormat
extends PhabricatorFileStorageFormat {
const FORMATKEY = 'aes-256-cbc';
private $keyName;
public function getStorageFormatName() {
return pht('Encrypted (AES-256-CBC)');
}
public function canGenerateNewKeyMaterial() {
return true;
}
public function generateNewKeyMaterial() {
$envelope = self::newAES256Key();
$material = $envelope->openEnvelope();
return base64_encode($material);
}
public function canCycleMasterKey() {
return true;
}
public function cycleStorageProperties() {
$file = $this->getFile();
list($key, $iv) = $this->extractKeyAndIV($file);
return $this->formatStorageProperties($key, $iv);
}
public function newReadIterator($raw_iterator) {
$file = $this->getFile();
$data = $file->loadDataFromIterator($raw_iterator);
list($key, $iv) = $this->extractKeyAndIV($file);
$data = $this->decryptData($data, $key, $iv);
return array($data);
}
public function newWriteIterator($raw_iterator) {
$file = $this->getFile();
$data = $file->loadDataFromIterator($raw_iterator);
list($key, $iv) = $this->extractKeyAndIV($file);
$data = $this->encryptData($data, $key, $iv);
return array($data);
}
public function newFormatIntegrityHash() {
$file = $this->getFile();
list($key_envelope, $iv_envelope) = $this->extractKeyAndIV($file);
// NOTE: We include the IV in the format integrity hash. If we do not,
// attackers can potentially forge the first block of decrypted data
// in CBC mode if they are able to substitute a chosen IV and predict
// the plaintext. (Normally, they can not tamper with the IV.)
$input = self::FORMATKEY.'/iv:'.$iv_envelope->openEnvelope();
return PhabricatorHash::digestWithNamedKey(
$input,
PhabricatorFileStorageEngine::HMAC_INTEGRITY);
}
public function newStorageProperties() {
// Generate a unique key and IV for this block of data.
$key_envelope = self::newAES256Key();
$iv_envelope = self::newAES256IV();
return $this->formatStorageProperties($key_envelope, $iv_envelope);
}
private function formatStorageProperties(
PhutilOpaqueEnvelope $key_envelope,
PhutilOpaqueEnvelope $iv_envelope) {
// Encode the raw binary data with base64 so we can wrap it in JSON.
$data = array(
'iv.base64' => base64_encode($iv_envelope->openEnvelope()),
'key.base64' => base64_encode($key_envelope->openEnvelope()),
);
// Encode the base64 data with JSON.
$data_clear = phutil_json_encode($data);
// Encrypt the block key with the master key, using a unique IV.
$data_iv = self::newAES256IV();
$key_name = $this->getMasterKeyName();
$master_key = $this->getMasterKeyMaterial($key_name);
$data_cipher = $this->encryptData($data_clear, $master_key, $data_iv);
return array(
'key.name' => $key_name,
'iv.base64' => base64_encode($data_iv->openEnvelope()),
'payload.base64' => base64_encode($data_cipher),
);
}
private function extractKeyAndIV(PhabricatorFile $file) {
$outer_iv = $file->getStorageProperty('iv.base64');
$outer_iv = base64_decode($outer_iv);
$outer_iv = new PhutilOpaqueEnvelope($outer_iv);
$outer_payload = $file->getStorageProperty('payload.base64');
$outer_payload = base64_decode($outer_payload);
$outer_key_name = $file->getStorageProperty('key.name');
$outer_key = $this->getMasterKeyMaterial($outer_key_name);
$payload = $this->decryptData($outer_payload, $outer_key, $outer_iv);
$payload = phutil_json_decode($payload);
$inner_iv = $payload['iv.base64'];
$inner_iv = base64_decode($inner_iv);
$inner_iv = new PhutilOpaqueEnvelope($inner_iv);
$inner_key = $payload['key.base64'];
$inner_key = base64_decode($inner_key);
$inner_key = new PhutilOpaqueEnvelope($inner_key);
return array($inner_key, $inner_iv);
}
private function encryptData(
$data,
PhutilOpaqueEnvelope $key,
PhutilOpaqueEnvelope $iv) {
$method = 'aes-256-cbc';
$key = $key->openEnvelope();
$iv = $iv->openEnvelope();
$result = openssl_encrypt($data, $method, $key, OPENSSL_RAW_DATA, $iv);
if ($result === false) {
throw new Exception(
pht(
'Failed to openssl_encrypt() data: %s',
openssl_error_string()));
}
return $result;
}
private function decryptData(
$data,
PhutilOpaqueEnvelope $key,
PhutilOpaqueEnvelope $iv) {
$method = 'aes-256-cbc';
$key = $key->openEnvelope();
$iv = $iv->openEnvelope();
$result = openssl_decrypt($data, $method, $key, OPENSSL_RAW_DATA, $iv);
if ($result === false) {
throw new Exception(
pht(
'Failed to openssl_decrypt() data: %s',
openssl_error_string()));
}
return $result;
}
public static function newAES256Key() {
// Unsurprisingly, AES256 uses a 256 bit key.
$key = Filesystem::readRandomBytes(phutil_units('256 bits in bytes'));
return new PhutilOpaqueEnvelope($key);
}
public static function newAES256IV() {
// AES256 uses a 256 bit key, but the initialization vector length is
// only 128 bits.
$iv = Filesystem::readRandomBytes(phutil_units('128 bits in bytes'));
return new PhutilOpaqueEnvelope($iv);
}
public function selectMasterKey($key_name) {
// Require that the key exist on the key ring.
$this->getMasterKeyMaterial($key_name);
$this->keyName = $key_name;
return $this;
}
private function getMasterKeyName() {
if ($this->keyName !== null) {
return $this->keyName;
}
$default = PhabricatorKeyring::getDefaultKeyName(self::FORMATKEY);
if ($default !== null) {
return $default;
}
throw new Exception(
pht(
'No AES256 key is specified in the keyring as a default encryption '.
'key, and no encryption key has been explicitly selected.'));
}
private function getMasterKeyMaterial($key_name) {
return PhabricatorKeyring::getKey($key_name, self::FORMATKEY);
}
}
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