Make Journal a general interface

This change moves the loading and saving mechanisms into its own
Plain- and EncryptedJournal subclasses for easier maintenance and lazy loading
of all the crypto modules.

jrnl/EncryptedJournal.py

@@ -0,0 +1,85 @@
+import hashlib
+import sys
+from . import Journal, util
+try:
+    from Crypto.Cipher import AES
+    from Crypto import Random
+    crypto_installed = True
+except ImportError:
+    crypto_installed = False
+
+
+def make_key(password):
+    return hashlib.sha256(password.encode("utf-8")).digest()
+
+
+def _decrypt(cipher, key):
+    """Decrypts a cipher string using self.key as the key and the first 16 byte of the cipher as the IV"""
+    if not crypto_installed:
+        sys.exit("Error: PyCrypto is not installed.")
+    if not cipher:
+        return ""
+    crypto = AES.new(key, AES.MODE_CBC, cipher[:16])
+    try:
+        plain = crypto.decrypt(cipher[16:])
+    except ValueError:
+        util.prompt("ERROR: Your journal file seems to be corrupted. You do have a backup, don't you?")
+        sys.exit(1)
+
+    padding_length = util.byte2int(plain[-1])
+    if padding_length > AES.block_size and padding_length != 32:
+        # 32 is the space character and is kept for backwards compatibility
+        return None
+    elif padding_length == 32:
+        plain = plain.strip()
+    elif plain[-padding_length:] != util.int2byte(padding_length) * padding_length:
+        # Invalid padding!
+        return None
+    else:
+        plain = plain[:-padding_length]
+
+    return plain.decode("utf-8")
+
+
+def _encrypt(plain, key):
+    """Encrypt a plaintext string using key"""
+    if not crypto_installed:
+        sys.exit("Error: PyCrypto is not installed.")
+    Random.atfork()  # A seed for PyCrypto
+    iv = Random.new().read(AES.block_size)
+    crypto = AES.new(key, AES.MODE_CBC, iv)
+    plain = plain.encode("utf-8")
+    padding_length = AES.block_size - len(plain) % AES.block_size
+    plain += util.int2byte(padding_length) * padding_length
+    return iv + crypto.encrypt(plain)
+
+
+class EncryptedJournal(Journal.Journal):
+    def __init__(self, name='default', **kwargs):
+        super(EncryptedJournal, self).__init__(name, **kwargs)
+        self.config['encrypt'] = True
+
+    def _load(self, filename):
+        with open(filename, "rb") as f:
+            journal_encrypted = f.read()
+
+        def validate_password(password):
+            key = make_key(password)
+            return _decrypt(journal_encrypted, key)
+
+        text = None
+
+        if 'password' in self.config:
+            text = validate_password(self.config['password'])
+
+        if text is None:
+            text = util.get_password(keychain=self.name, validator=validate_password)
+
+        return text
+
+    def _store(self, filename, text):
+        key = make_key(self.config['password'])
+        journal = _encrypt(text, key)
+
+        with open(filename, 'wb') as f:
+            f.write(journal)