diff options
Diffstat (limited to 'src/leap/soledad/backends/sqlcipher.py')
| -rw-r--r-- | src/leap/soledad/backends/sqlcipher.py | 449 |
1 files changed, 408 insertions, 41 deletions
diff --git a/src/leap/soledad/backends/sqlcipher.py b/src/leap/soledad/backends/sqlcipher.py index f174f0a7..5825b844 100644 --- a/src/leap/soledad/backends/sqlcipher.py +++ b/src/leap/soledad/backends/sqlcipher.py @@ -16,10 +16,37 @@ # along with this program. If not, see <http://www.gnu.org/licenses/>. -"""A U1DB backend that uses SQLCipher as its persistence layer.""" +""" +A U1DB backend that uses SQLCipher as its persistence layer. + +The SQLCipher API (http://sqlcipher.net/sqlcipher-api/) is fully implemented, +with the exception of the following statements: + + * PRAGMA cipher_use_hmac + * PRAGMA cipher_default_use_mac + +SQLCipher 2.0 introduced a per-page HMAC to validate that the page data has +not be tampered with. By default, when creating or opening a database using +SQLCipher 2, SQLCipher will attempt to use an HMAC check. This change in +database format means that SQLCipher 2 can't operate on version 1.1.x +databases by default. Thus, in order to provide backward compatibility with +SQLCipher 1.1.x, PRAGMA cipher_use_hmac can be used to disable the HMAC +functionality on specific databases. + +In some very specific cases, it is not possible to call PRAGMA cipher_use_hmac +as one of the first operations on a database. An example of this is when +trying to ATTACH a 1.1.x database to the main database. In these cases PRAGMA +cipher_default_use_hmac can be used to globally alter the default use of HMAC +when opening a database. + +So, as the statements above were introduced for backwards compatibility with +SLCipher 1.1 databases, we do not implement them as all SQLCipher databases +handled by Soledad should be created by SQLCipher >= 2.0. +""" import os import time +import string from u1db.backends import sqlite_backend @@ -34,7 +61,9 @@ from leap.soledad.backends.leap_backend import LeapDocument sqlite_backend.dbapi2 = dbapi2 -def open(path, password, create=True, document_factory=None, crypto=None): +def open(path, password, create=True, document_factory=None, crypto=None, + raw_key=False, cipher='aes-256-cbc', kdf_iter=4000, + cipher_page_size=1024): """Open a database at the given location. Will raise u1db.errors.DatabaseDoesNotExist if create=False and the @@ -48,15 +77,32 @@ def open(path, password, create=True, document_factory=None, crypto=None): @param document_factory: A function that will be called with the same parameters as Document.__init__. @type document_factory: callable + @param crypto: An instance of SoledadCrypto so we can encrypt/decrypt + document contents when syncing. + @type crypto: soledad.crypto.SoledadCrypto + @param raw_key: Whether C{password} is a raw 64-char hex string or a + passphrase that should be hashed to obtain the encyrption key. + @type raw_key: bool + @param cipher: The cipher and mode to use. + @type cipher: str + @param kdf_iter: The number of iterations to use. + @type kdf_iter: int + @param cipher_page_size: The page size. + @type cipher_page_size: int @return: An instance of Database. @rtype SQLCipherDatabase """ return SQLCipherDatabase.open_database( path, password, create=create, document_factory=document_factory, - crypto=crypto) + crypto=crypto, raw_key=raw_key, cipher=cipher, kdf_iter=kdf_iter, + cipher_page_size=cipher_page_size) +# +# Exceptions +# + class DatabaseIsNotEncrypted(Exception): """ Exception raised when trying to open non-encrypted databases. @@ -64,17 +110,25 @@ class DatabaseIsNotEncrypted(Exception): pass +class NotAnHexString(Exception): + """ + Raised when trying to (raw) key the database with a non-hex string. + """ + pass + + +# +# The SQLCipher database +# + class SQLCipherDatabase(sqlite_backend.SQLitePartialExpandDatabase): """A U1DB implementation that uses SQLCipher as its persistence layer.""" _index_storage_value = 'expand referenced encrypted' - @classmethod - def set_pragma_key(cls, db_handle, key): - db_handle.cursor().execute("PRAGMA key = '%s'" % key) - def __init__(self, sqlcipher_file, password, document_factory=None, - crypto=None): + crypto=None, raw_key=False, cipher='aes-256-cbc', + kdf_iter=4000, cipher_page_size=1024): """ Create a new sqlcipher file. @@ -88,10 +142,27 @@ class SQLCipherDatabase(sqlite_backend.SQLitePartialExpandDatabase): @param crypto: An instance of SoledadCrypto so we can encrypt/decrypt document contents when syncing. @type crypto: soledad.crypto.SoledadCrypto + @param raw_key: Whether C{password} is a raw 64-char hex string or a + passphrase that should be hashed to obtain the encyrption key. + @type raw_key: bool + @param cipher: The cipher and mode to use. + @type cipher: str + @param kdf_iter: The number of iterations to use. + @type kdf_iter: int + @param cipher_page_size: The page size. + @type cipher_page_size: int """ - self._check_if_db_is_encrypted(sqlcipher_file) + # ensure the db is encrypted if the file already exists + if os.path.exists(sqlcipher_file): + self.assert_db_is_encrypted( + sqlcipher_file, password, raw_key, cipher, kdf_iter, + cipher_page_size) + # connect to the database self._db_handle = dbapi2.connect(sqlcipher_file) - SQLCipherDatabase.set_pragma_key(self._db_handle, password) + # set SQLCipher cryptographic parameters + self._set_crypto_pragmas( + self._db_handle, password, raw_key, cipher, kdf_iter, + cipher_page_size) self._real_replica_uid = None self._ensure_schema() self._crypto = crypto @@ -103,30 +174,10 @@ class SQLCipherDatabase(sqlite_backend.SQLitePartialExpandDatabase): syncable=syncable) self.set_document_factory(factory) - def _check_if_db_is_encrypted(self, sqlcipher_file): - """ - Verify if loca file is an encrypted database. - - @param sqlcipher_file: The path for the SQLCipher file. - @type sqlcipher_file: str - - @return: True if the database is encrypted, False otherwise. - @rtype: bool - """ - if not os.path.exists(sqlcipher_file): - return - else: - try: - # try to open an encrypted database with the regular u1db - # backend should raise a DatabaseError exception. - sqlite_backend.SQLitePartialExpandDatabase(sqlcipher_file) - raise DatabaseIsNotEncrypted() - except dbapi2.DatabaseError: - pass - @classmethod def _open_database(cls, sqlcipher_file, password, document_factory=None, - crypto=None): + crypto=None, raw_key=False, cipher='aes-256-cbc', + kdf_iter=4000, cipher_page_size=1024): """ Open a SQLCipher database. @@ -140,6 +191,15 @@ class SQLCipherDatabase(sqlite_backend.SQLitePartialExpandDatabase): @param crypto: An instance of SoledadCrypto so we can encrypt/decrypt document contents when syncing. @type crypto: soledad.crypto.SoledadCrypto + @param raw_key: Whether C{password} is a raw 64-char hex string or a + passphrase that should be hashed to obtain the encyrption key. + @type raw_key: bool + @param cipher: The cipher and mode to use. + @type cipher: str + @param kdf_iter: The number of iterations to use. + @type kdf_iter: int + @param cipher_page_size: The page size. + @type cipher_page_size: int @return: The database object. @rtype: SQLCipherDatabase @@ -152,7 +212,10 @@ class SQLCipherDatabase(sqlite_backend.SQLitePartialExpandDatabase): # where without re-opening the database on Windows, it # doesn't see the transaction that was just committed db_handle = dbapi2.connect(sqlcipher_file) - SQLCipherDatabase.set_pragma_key(db_handle, password) + # set cryptographic params + cls._set_crypto_pragmas( + db_handle, password, raw_key, cipher, kdf_iter, + cipher_page_size) c = db_handle.cursor() v, err = cls._which_index_storage(c) db_handle.close() @@ -166,11 +229,14 @@ class SQLCipherDatabase(sqlite_backend.SQLitePartialExpandDatabase): time.sleep(cls.WAIT_FOR_PARALLEL_INIT_HALF_INTERVAL) return SQLCipherDatabase._sqlite_registry[v]( sqlcipher_file, password, document_factory=document_factory, - crypto=crypto) + crypto=crypto, raw_key=raw_key, cipher=cipher, kdf_iter=kdf_iter, + cipher_page_size=cipher_page_size) @classmethod def open_database(cls, sqlcipher_file, password, create, backend_cls=None, - document_factory=None, crypto=None): + document_factory=None, crypto=None, raw_key=False, + cipher='aes-256-cbc', kdf_iter=4000, + cipher_page_size=1024): """ Open a SQLCipher database. @@ -189,14 +255,24 @@ class SQLCipherDatabase(sqlite_backend.SQLitePartialExpandDatabase): @param crypto: An instance of SoledadCrypto so we can encrypt/decrypt document contents when syncing. @type crypto: soledad.crypto.SoledadCrypto + @param raw_key: Whether C{password} is a raw 64-char hex string or a + passphrase that should be hashed to obtain the encyrption key. + @type raw_key: bool + @param cipher: The cipher and mode to use. + @type cipher: str + @param kdf_iter: The number of iterations to use. + @type kdf_iter: int + @param cipher_page_size: The page size. + @type cipher_page_size: int @return: The database object. @rtype: SQLCipherDatabase """ try: - return cls._open_database(sqlcipher_file, password, - document_factory=document_factory, - crypto=crypto) + return cls._open_database( + sqlcipher_file, password, document_factory=document_factory, + crypto=crypto, raw_key=raw_key, cipher=cipher, + kdf_iter=kdf_iter, cipher_page_size=cipher_page_size) except errors.DatabaseDoesNotExist: if not create: raise @@ -204,9 +280,10 @@ class SQLCipherDatabase(sqlite_backend.SQLitePartialExpandDatabase): if backend_cls is None: # default is SQLCipherPartialExpandDatabase backend_cls = SQLCipherDatabase - return backend_cls(sqlcipher_file, password, - document_factory=document_factory, - crypto=crypto) + return backend_cls( + sqlcipher_file, password, document_factory=document_factory, + crypto=crypto, raw_key=raw_key, cipher=cipher, + kdf_iter=kdf_iter, cipher_page_size=cipher_page_size) def sync(self, url, creds=None, autocreate=True): """ @@ -283,4 +360,294 @@ class SQLCipherDatabase(sqlite_backend.SQLitePartialExpandDatabase): doc.syncable = bool(result[0]) return doc + # + # SQLCipher API methods + # + + @classmethod + def assert_db_is_encrypted(cls, sqlcipher_file, key, raw_key, cipher, + kdf_iter, cipher_page_size): + """ + Assert that C{sqlcipher_file} contains an encrypted database. + + When opening an existing database, PRAGMA key will not immediately + throw an error if the key provided is incorrect. To test that the + database can be successfully opened with the provided key, it is + necessary to perform some operation on the database (i.e. read from + it) and confirm it is success. + + The easiest way to do this is select off the sqlite_master table, + which will attempt to read the first page of the database and will + parse the schema. + + @param sqlcipher_file: The path for the SQLCipher file. + @type sqlcipher_file: str + @param key: The key that protects the SQLCipher db. + @type key: str + @param raw_key: Whether C{key} is a raw 64-char hex string or a + passphrase that should be hashed to obtain the encyrption key. + @type raw_key: bool + @param cipher: The cipher and mode to use. + @type cipher: str + @param kdf_iter: The number of iterations to use. + @type kdf_iter: int + @param cipher_page_size: The page size. + @type cipher_page_size: int + """ + try: + # try to open an encrypted database with the regular u1db + # backend should raise a DatabaseError exception. + sqlite_backend.SQLitePartialExpandDatabase(sqlcipher_file) + raise DatabaseIsNotEncrypted() + except dbapi2.DatabaseError: + # assert that we can access it using SQLCipher with the given + # key + db_handle = dbapi2.connect(sqlcipher_file) + cls._set_crypto_pragmas( + db_handle, key, raw_key, cipher, kdf_iter, cipher_page_size) + db_handle.cursor().execute('SELECT count(*) FROM sqlite_master') + + @classmethod + def _set_crypto_pragmas(cls, db_handle, key, raw_key, cipher, kdf_iter, + cipher_page_size): + """ + Set cryptographic params (key, cipher, KDF number of iterations and + cipher page size). + """ + cls._pragma_key(db_handle, key, raw_key) + cls._pragma_cipher(db_handle, cipher) + cls._pragma_kdf_iter(db_handle, kdf_iter) + cls._pragma_cipher_page_size(db_handle, cipher_page_size) + + @classmethod + def _pragma_key(cls, db_handle, key, raw_key): + """ + Set the C{key} for use with the database. + + The process of creating a new, encrypted database is called 'keying' + the database. SQLCipher uses just-in-time key derivation at the point + it is first needed for an operation. This means that the key (and any + options) must be set before the first operation on the database. As + soon as the database is touched (e.g. SELECT, CREATE TABLE, UPDATE, + etc.) and pages need to be read or written, the key is prepared for + use. + + Implementation Notes: + + * PRAGMA key should generally be called as the first operation on a + database. + + @param key: The key for use with the database. + @type key: str + @param raw_key: Whether C{key} is a raw 64-char hex string or a + passphrase that should be hashed to obtain the encyrption key. + @type raw_key: bool + """ + if raw_key: + cls._pragma_key_raw(db_handle, key) + else: + cls._pragma_key_passphrase(db_handle, key) + + @classmethod + def _pragma_key_passphrase(cls, db_handle, passphrase): + """ + Set a passphrase for encryption key derivation. + + The key itself can be a passphrase, which is converted to a key using + PBKDF2 key derivation. The result is used as the encryption key for + the database. By using this method, there is no way to alter the KDF; + if you want to do so you should use a raw key instead and derive the + key using your own KDF. + + @param db_handle: A handle to the SQLCipher database. + @type db_handle: pysqlcipher.Connection + @param passphrase: The passphrase used to derive the encryption key. + @type passphrase: str + """ + db_handle.cursor().execute("PRAGMA key = '%s'" % passphrase) + + @classmethod + def _pragma_key_raw(cls, db_handle, key): + """ + Set a raw hexadecimal encryption key. + + It is possible to specify an exact byte sequence using a blob literal. + With this method, it is the calling application's responsibility to + ensure that the data provided is a 64 character hex string, which will + be converted directly to 32 bytes (256 bits) of key data. + + @param db_handle: A handle to the SQLCipher database. + @type db_handle: pysqlcipher.Connection + @param key: A 64 character hex string. + @type key: str + """ + if not all(c in string.hexdigits for c in key): + raise NotAnHexString(key) + db_handle.cursor().execute('PRAGMA key = "x\'%s"' % passphrase) + + @classmethod + def _pragma_cipher(cls, db_handle, cipher='aes-256-cbc'): + """ + Set the cipher and mode to use for symmetric encryption. + + SQLCipher uses aes-256-cbc as the default cipher and mode of + operation. It is possible to change this, though not generally + recommended, using PRAGMA cipher. + + SQLCipher makes direct use of libssl, so all cipher options available + to libssl are also available for use with SQLCipher. See `man enc` for + OpenSSL's supported ciphers. + + Implementation Notes: + + * PRAGMA cipher must be called after PRAGMA key and before the first + actual database operation or it will have no effect. + + * If a non-default value is used PRAGMA cipher to create a database, + it must also be called every time that database is opened. + + * SQLCipher does not implement its own encryption. Instead it uses the + widely available and peer-reviewed OpenSSL libcrypto for all + cryptographic functions. + + @param db_handle: A handle to the SQLCipher database. + @type db_handle: pysqlcipher.Connection + @param cipher: The cipher and mode to use. + @type cipher: str + """ + db_handle.cursor().execute("PRAGMA cipher = '%s'" % cipher) + + @classmethod + def _pragma_kdf_iter(cls, db_handle, kdf_iter=4000): + """ + Set the number of iterations for the key derivation function. + + SQLCipher uses PBKDF2 key derivation to strengthen the key and make it + resistent to brute force and dictionary attacks. The default + configuration uses 4000 PBKDF2 iterations (effectively 16,000 SHA1 + operations). PRAGMA kdf_iter can be used to increase or decrease the + number of iterations used. + + Implementation Notes: + + * PRAGMA kdf_iter must be called after PRAGMA key and before the first + actual database operation or it will have no effect. + + * If a non-default value is used PRAGMA kdf_iter to create a database, + it must also be called every time that database is opened. + + * It is not recommended to reduce the number of iterations if a + passphrase is in use. + + @param db_handle: A handle to the SQLCipher database. + @type db_handle: pysqlcipher.Connection + @param kdf_iter: The number of iterations to use. + @type kdf_iter: int + """ + db_handle.cursor().execute("PRAGMA kdf_iter = '%d'" % kdf_iter) + + @classmethod + def _pragma_cipher_page_size(cls, db_handle, cipher_page_size=1024): + """ + Set the page size of the encrypted database. + + SQLCipher 2 introduced the new PRAGMA cipher_page_size that can be + used to adjust the page size for the encrypted database. The default + page size is 1024 bytes, but it can be desirable for some applications + to use a larger page size for increased performance. For instance, + some recent testing shows that increasing the page size can noticeably + improve performance (5-30%) for certain queries that manipulate a + large number of pages (e.g. selects without an index, large inserts in + a transaction, big deletes). + + To adjust the page size, call the pragma immediately after setting the + key for the first time and each subsequent time that you open the + database. + + Implementation Notes: + + * PRAGMA cipher_page_size must be called after PRAGMA key and before + the first actual database operation or it will have no effect. + + * If a non-default value is used PRAGMA cipher_page_size to create a + database, it must also be called every time that database is opened. + + @param db_handle: A handle to the SQLCipher database. + @type db_handle: pysqlcipher.Connection + @param cipher_page_size: The page size. + @type cipher_page_size: int + """ + db_handle.cursor().execute( + "PRAGMA cipher_page_size = '%d'" % cipher_page_size) + + @classmethod + def _pragma_rekey(cls, db_handle, new_key, raw_key): + """ + Change the key of an existing encrypted database. + + To change the key on an existing encrypted database, it must first be + unlocked with the current encryption key. Once the database is + readable and writeable, PRAGMA rekey can be used to re-encrypt every + page in the database with a new key. + + * PRAGMA rekey must be called after PRAGMA key. It can be called at any + time once the database is readable. + + * PRAGMA rekey can not be used to encrypted a standard SQLite + database! It is only useful for changing the key on an existing + database. + + * Previous versions of SQLCipher provided a PRAGMA rekey_cipher and + code>PRAGMA rekey_kdf_iter. These are deprecated and should not be + used. Instead, use sqlcipher_export(). + + @param db_handle: A handle to the SQLCipher database. + @type db_handle: pysqlcipher.Connection + @param new_key: The new key. + @type new_key: str + @param raw_key: Whether C{password} is a raw 64-char hex string or a + passphrase that should be hashed to obtain the encyrption key. + @type raw_key: bool + """ + if raw_key: + cls._pragma_rekey_raw(db_handle, key) + else: + cls._pragma_rekey_passphrase(db_handle, key) + + @classmethod + def _pragma_rekey_passphrase(cls, db_handle, passphrase): + """ + Change the passphrase for encryption key derivation. + + The key itself can be a passphrase, which is converted to a key using + PBKDF2 key derivation. The result is used as the encryption key for + the database. + + @param db_handle: A handle to the SQLCipher database. + @type db_handle: pysqlcipher.Connection + @param passphrase: The passphrase used to derive the encryption key. + @type passphrase: str + """ + db_handle.cursor().execute("PRAGMA rekey = '%s'" % passphrase) + + @classmethod + def _pragma_rekey_raw(cls, db_handle, key): + """ + Change the raw hexadecimal encryption key. + + It is possible to specify an exact byte sequence using a blob literal. + With this method, it is the calling application's responsibility to + ensure that the data provided is a 64 character hex string, which will + be converted directly to 32 bytes (256 bits) of key data. + + @param db_handle: A handle to the SQLCipher database. + @type db_handle: pysqlcipher.Connection + @param key: A 64 character hex string. + @type key: str + """ + if not all(c in string.hexdigits for c in key): + raise NotAnHexString(key) + db_handle.cursor().execute('PRAGMA rekey = "x\'%s"' % passphrase) + + sqlite_backend.SQLiteDatabase.register_implementation(SQLCipherDatabase) |