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<?php
namespace Defuse\Crypto;
use Defuse\Crypto\Exception as Ex;
final class KeyProtectedByPassword
{
const PASSWORD_KEY_CURRENT_VERSION = "\xDE\xF1\x00\x00";
/**
* @var string
*/
private $encrypted_key = '';
/**
* Creates a random key protected by the provided password.
*
* @param string $password
*
* @throws Ex\EnvironmentIsBrokenException
*
* @return KeyProtectedByPassword
*/
public static function createRandomPasswordProtectedKey($password)
{
$inner_key = Key::createNewRandomKey();
/* The password is hashed as a form of poor-man's domain separation
* between this use of encryptWithPassword() and other uses of
* encryptWithPassword() that the user may also be using as part of the
* same protocol. */
$encrypted_key = Crypto::encryptWithPassword(
$inner_key->saveToAsciiSafeString(),
\hash(Core::HASH_FUNCTION_NAME, $password, true),
true
);
return new KeyProtectedByPassword($encrypted_key);
}
/**
* Loads a KeyProtectedByPassword from its encoded form.
*
* @param string $saved_key_string
*
* @throws Ex\BadFormatException
*
* @return KeyProtectedByPassword
*/
public static function loadFromAsciiSafeString($saved_key_string)
{
$encrypted_key = Encoding::loadBytesFromChecksummedAsciiSafeString(
self::PASSWORD_KEY_CURRENT_VERSION,
$saved_key_string
);
return new KeyProtectedByPassword($encrypted_key);
}
/**
* Encodes the KeyProtectedByPassword into a string of printable ASCII
* characters.
*
* @throws Ex\EnvironmentIsBrokenException
*
* @return string
*/
public function saveToAsciiSafeString()
{
return Encoding::saveBytesToChecksummedAsciiSafeString(
self::PASSWORD_KEY_CURRENT_VERSION,
$this->encrypted_key
);
}
/**
* Decrypts the protected key, returning an unprotected Key object that can
* be used for encryption and decryption.
*
* @throws Ex\EnvironmentIsBrokenException
* @throws Ex\WrongKeyOrModifiedCiphertextException
*
* @param string $password
* @return Key
*/
public function unlockKey($password)
{
try {
$inner_key_encoded = Crypto::decryptWithPassword(
$this->encrypted_key,
\hash(Core::HASH_FUNCTION_NAME, $password, true),
true
);
return Key::loadFromAsciiSafeString($inner_key_encoded);
} catch (Ex\BadFormatException $ex) {
/* This should never happen unless an attacker replaced the
* encrypted key ciphertext with some other ciphertext that was
* encrypted with the same password. We transform the exception type
* here in order to make the API simpler, avoiding the need to
* document that this method might throw an Ex\BadFormatException. */
throw new Ex\WrongKeyOrModifiedCiphertextException(
"The decrypted key was found to be in an invalid format. " .
"This very likely indicates it was modified by an attacker."
);
}
}
/**
* Changes the password.
*
* @param string $current_password
* @param string $new_password
*
* @throws Ex\EnvironmentIsBrokenException
* @throws Ex\WrongKeyOrModifiedCiphertextException
*
* @return KeyProtectedByPassword
*/
public function changePassword($current_password, $new_password)
{
$inner_key = $this->unlockKey($current_password);
/* The password is hashed as a form of poor-man's domain separation
* between this use of encryptWithPassword() and other uses of
* encryptWithPassword() that the user may also be using as part of the
* same protocol. */
$encrypted_key = Crypto::encryptWithPassword(
$inner_key->saveToAsciiSafeString(),
\hash(Core::HASH_FUNCTION_NAME, $new_password, true),
true
);
$this->encrypted_key = $encrypted_key;
return $this;
}
/**
* Constructor for KeyProtectedByPassword.
*
* @param string $encrypted_key
*/
private function __construct($encrypted_key)
{
$this->encrypted_key = $encrypted_key;
}
}
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