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Diffstat (limited to 'client/src/leap/soledad/client/pragmas.py')
-rw-r--r-- | client/src/leap/soledad/client/pragmas.py | 349 |
1 files changed, 349 insertions, 0 deletions
diff --git a/client/src/leap/soledad/client/pragmas.py b/client/src/leap/soledad/client/pragmas.py new file mode 100644 index 00000000..a21e68a8 --- /dev/null +++ b/client/src/leap/soledad/client/pragmas.py @@ -0,0 +1,349 @@ +# -*- coding: utf-8 -*- +# pragmas.py +# Copyright (C) 2013, 2014 LEAP +# +# This program is free software: you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation, either version 3 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program. If not, see <http://www.gnu.org/licenses/>. +""" +Different pragmas used in the SQLCIPHER database. +""" +# TODO --------------------------------------------------------------- +# Work In Progress. +# We need to reduce the impedance mismatch between the current soledad +# implementation and the eventually asynchronous api. +# So... how to plug it in, allowing for an optional sync / async coexistence? +# One of the first things is to isolate all the pragmas work that has to be +# done during initialization. +# And, instead of having all of them passed the db_handle and executing that, +# we could have just a string returned, that can be chained to a deferred. +# --------------------------------------------------------------------- +import logging +import string + +logger = logging.getLogger(__name__) + + +def set_crypto_pragmas(db_handle, sqlcipher_opts): + """ + Set cryptographic params (key, cipher, KDF number of iterations and + cipher page size). + + :param db_handle: + :type db_handle: + :param sqlcipher_opts: options for the SQLCipherDatabase + :type sqlcipher_opts: SQLCipherOpts instance + """ + # XXX assert CryptoOptions + opts = sqlcipher_opts + _set_key(db_handle, opts.key, opts.is_raw_key) + _set_cipher(db_handle, opts.cipher) + _set_kdf_iter(db_handle, opts.kdf_iter) + _set_cipher_page_size(db_handle, opts.cipher_page_size) + + +def _set_key(db_handle, key, is_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 is_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 is_raw_key: bool + """ + if is_raw_key: + _set_key_raw(db_handle, key) + else: + _set_key_passphrase(db_handle, key) + + +def _set_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) + + +def _set_key_raw(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"' % key) + + +def _set_cipher(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) + + +def _set_kdf_iter(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) + + +def _set_cipher_page_size(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) + + +# XXX UNUSED ? +def set_rekey(db_handle, new_key, is_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 is_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 is_raw_key: bool + """ + if is_raw_key: + _set_rekey_raw(db_handle, new_key) + else: + _set_rekey_passphrase(db_handle, new_key) + + +def _set_rekey_passphrase(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) + + +def _set_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"' % key) + + +def set_synchronous_off(db_handle): + """ + Change the setting of the "synchronous" flag to OFF. + """ + logger.debug("SQLCIPHER: SETTING SYNCHRONOUS OFF") + db_handle.cursor().execute('PRAGMA synchronous=OFF') + + +def set_synchronous_normal(db_handle): + """ + Change the setting of the "synchronous" flag to NORMAL. + """ + logger.debug("SQLCIPHER: SETTING SYNCHRONOUS NORMAL") + db_handle.cursor().execute('PRAGMA synchronous=NORMAL') + + +def set_mem_temp_store(cls, db_handle): + """ + Use a in-memory store for temporary tables. + """ + logger.debug("SQLCIPHER: SETTING TEMP_STORE MEMORY") + db_handle.cursor().execute('PRAGMA temp_store=MEMORY') + + +def set_write_ahead_logging(cls, db_handle): + """ + Enable write-ahead logging, and set the autocheckpoint to 50 pages. + + Setting the autocheckpoint to a small value, we make the reads not + suffer too much performance degradation. + + From the sqlite docs: + + "There is a tradeoff between average read performance and average write + performance. To maximize the read performance, one wants to keep the + WAL as small as possible and hence run checkpoints frequently, perhaps + as often as every COMMIT. To maximize write performance, one wants to + amortize the cost of each checkpoint over as many writes as possible, + meaning that one wants to run checkpoints infrequently and let the WAL + grow as large as possible before each checkpoint. The decision of how + often to run checkpoints may therefore vary from one application to + another depending on the relative read and write performance + requirements of the application. The default strategy is to run a + checkpoint once the WAL reaches 1000 pages" + """ + logger.debug("SQLCIPHER: SETTING WRITE-AHEAD LOGGING") + db_handle.cursor().execute('PRAGMA journal_mode=WAL') + # The optimum value can still use a little bit of tuning, but we favor + # small sizes of the WAL file to get fast reads, since we assume that + # the writes will be quick enough to not block too much. + + # TODO + # As a further improvement, we might want to set autocheckpoint to 0 + # here and do the checkpoints manually in a separate thread, to avoid + # any blocks in the main thread (we should run a loopingcall from here) + db_handle.cursor().execute('PRAGMA wal_autocheckpoint=50') + + +class NotAnHexString(Exception): + """ + Raised when trying to (raw) key the database with a non-hex string. + """ + pass |