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introduce wrapped_openssl_seal() and wrapped_openssl_open() #35916

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introduce wrapped_openssl_seal() and wrapped_openssl_open() #35916

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166 changes: 164 additions & 2 deletions apps/encryption/lib/Crypto/Crypt.php
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@
* @author Roeland Jago Douma <roeland@famdouma.nl>
* @author Stefan Weiberg <sweiberg@suse.com>
* @author Thomas Müller <thomas.mueller@tmit.eu>
* @author Kevin Niehage <kevin@niehage.name>
*
* @license AGPL-3.0
*
Expand Down Expand Up @@ -98,6 +99,9 @@ class Crypt {
/** @var bool */
private $supportLegacy;

/** @var bool */
private $wrapRC4 = false;

/**
* Use the legacy base64 encoding instead of the more space-efficient binary encoding.
*/
Expand All @@ -116,6 +120,24 @@ public function __construct(ILogger $logger, IUserSession $userSession, IConfig
$this->l = $l;
$this->supportLegacy = $this->config->getSystemValueBool('encryption.legacy_format_support', false);
$this->useLegacyBase64Encoding = $this->config->getSystemValueBool('encryption.use_legacy_base64_encoding', false);
$this->wrapRC4 = $this->checkWrapRC4();
}

/**
* checks if RC4 via OpenSSL works as expected
*
* @return bool
*/
public function checkWrapRC4() {
// with OpenSSL v3 we assume that we have to replace the RC4 algo
$result = (OPENSSL_VERSION_NUMBER >= 0x30000000);

if ($result) {
// maybe someone has re-enabled the legacy support in OpenSSL v3
$result = (false === openssl_encrypt("test", "rc4", "test", OPENSSL_RAW_DATA, "", $tag, "", 0));
}

return $result;
}

/**
Expand Down Expand Up @@ -707,7 +729,7 @@ public function multiKeyDecrypt($encKeyFile, $shareKey, $privateKey) {
throw new MultiKeyDecryptException('Cannot multikey decrypt empty plain content');
}

if (openssl_open($encKeyFile, $plainContent, $shareKey, $privateKey, 'RC4')) {
if ($this->wrapped_openssl_open($encKeyFile, $plainContent, $shareKey, $privateKey, 'RC4')) {
return $plainContent;
} else {
throw new MultiKeyDecryptException('multikeydecrypt with share key failed:' . openssl_error_string());
Expand All @@ -732,7 +754,7 @@ public function multiKeyEncrypt($plainContent, array $keyFiles) {
$shareKeys = [];
$mappedShareKeys = [];

if (openssl_seal($plainContent, $sealed, $shareKeys, $keyFiles, 'RC4')) {
if ($this->wrapped_openssl_seal($plainContent, $sealed, $shareKeys, $keyFiles, 'RC4')) {
$i = 0;

// Ensure each shareKey is labelled with its corresponding key id
Expand All @@ -750,7 +772,147 @@ public function multiKeyEncrypt($plainContent, array $keyFiles) {
}
}

/**
* returns the value of $useLegacyBase64Encoding
*
* @return bool
*/
public function useLegacyBase64Encoding(): bool {
return $this->useLegacyBase64Encoding;
}

/**
* implements RC4
*
* @param $data
* @param $secret
* @return string
*/
public function rc4($data, $secret) {
// initialize $result
$result = "";

// initialize $state
$state = [];
for ($i = 0x00; $i <= 0xFF; $i++) {
$state[$i] = $i;
}

// mix $secret into $state
$indexA = 0x00;
$indexB = 0x00;
for ($i = 0x00; $i <= 0xFF; $i++) {
$indexB = ($indexB + ord($secret[$indexA]) + $state[$i]) % 0x100;

$tmp = $state[$i];
$state[$i] = $state[$indexB];
$state[$indexB] = $tmp;

$indexA = ($indexA + 0x01) % strlen($secret);
}

// decrypt $data with $state
$indexA = 0x00;
$indexB = 0x00;
for ($i = 0x00; $i < strlen($data); $i++) {
$indexA = ($indexA + 0x01) % 0x100;
$indexB = ($state[$indexA] + $indexB) % 0x100;

$tmp = $state[$indexA];
$state[$indexA] = $state[$indexB];
$state[$indexB] = $tmp;

$result .= chr(ord($data[$i]) ^ $state[($state[$indexA] + $state[$indexB]) % 0x100]);
}

return $result;
}

/**
* wraps openssl_open() for cases where RC4 is not supported by OpenSSL v3
* and replaces it with a custom implementation where necessary
*
* @param $data
* @param $output
* @param $encrypted_key
* @param $private_key
* @param $cipher_algo
* @param $iv
* @return bool
*/
public function wrapped_openssl_open($data, &$output, $encrypted_key, $private_key, $cipher_algo, $iv = null) {
$result = false;

// check if RC4 is used and if we need to wrap RC4
if ((0 === strcasecmp($cipher_algo, "rc4")) && $this->wrapRC4) {
// decrypt the intermediate key with RSA
if (openssl_private_decrypt($encrypted_key, $intermediate, $private_key, OPENSSL_PKCS1_PADDING)) {
// decrypt the file key with the intermediate key
// using our own RC4 implementation
$output = $this->rc4($data, $intermediate);
$result = (strlen($output) === strlen($data));
}
} else {
// use the default implementation instead
$result = openssl_open($data, $output, $encrypted_key, $private_key, $cipher_algo, $iv);
}

return $result;
}

/**
* wraps openssl_seal() for cases where RC4 is not supported by OpenSSL v3
* and replaces it with a custom implementation where necessary
*
* @param $data
* @param $sealed_data
* @param $encrypted_keys
* @param $public_key
* @param $cipher_algo
* @param $iv
* @return bool|int
*/
public function wrapped_openssl_seal($data, &$sealed_data, &$encrypted_keys, $public_key, $cipher_algo, $iv = null) {
$result = false;

// check if RC4 is used and if we need to wrap RC4
if ((0 === strcasecmp($cipher_algo, "rc4")) && $this->wrapRC4) {
// make sure that there is at least one public key to use
if (is_array($public_key) && (1 <= count($public_key))) {
// generate the intermediate key
$intermediate = openssl_random_pseudo_bytes(16, $strong_result);

// check if we got strong random data
if ($strong_result) {
// encrypt the file key with the intermediate key
// using our own RC4 implementation
$sealed_data = $this->rc4($data, $intermediate);
if (strlen($sealed_data) === strlen($data)) {
// prepare the encrypted keys
$encrypted_keys = [];

// iterate over the public keys and encrypt the intermediate
// for each of them with RSA
foreach ($public_key as $tmp_key) {
if (openssl_public_encrypt($intermediate, $tmp_output, $tmp_key, OPENSSL_PKCS1_PADDING)) {
$encrypted_keys[] = $tmp_output;
}
}

// set the result if everything worked fine
if (count($public_key) === count($encrypted_keys)) {
$result = strlen($sealed_data);
}
}
}
}

} else {
// use the default implementation instead
$result = openssl_seal($data, $sealed_data, $encrypted_keys, $public_key, $cipher_algo, $iv);
}

return $result;
}

}