Added support for the infrastructure for on demand access/create the

server connection.

The BaseDriver and BaseConnection are two abstract classes, which allows
us to replace the existing driver with the currently used. The current
implementation supports to connect the PostgreSQL and Postgres Plus
Advanced Server using the psycopg2 driver.

web/pgadmin/utils/crypto.py

@@ -0,0 +1,69 @@
+##########################################################################
+#
+# pgAdmin 4 - PostgreSQL Tools
+#
+# Copyright (C) 2013 - 2015, The pgAdmin Development Team
+# This software is released under the PostgreSQL Licence
+#
+#########################################################################
+"""This File Provides Cryptography."""
+
+from Crypto.Cipher import AES
+from Crypto import Random
+import base64
+
+padding_string = '}'
+
+
+def encrypt(plaintext, key):
+    """
+    Encrypt the plaintext with AES method.
+
+    Parameters:
+        plaintext -- String to be encrypted.
+        key       -- Key for encryption.
+    """
+
+    iv = Random.new().read(AES.block_size)
+    cipher = AES.new(pad(key), AES.MODE_CFB, iv)
+    excrypted = base64.b64encode(iv + cipher.encrypt(plaintext))
+
+    return excrypted
+
+
+def decrypt(ciphertext, key):
+    """
+    Decrypt the AES encrypted string.
+
+    Parameters:
+        ciphertext -- Encrypted string with AES method.
+        key        -- key to decrypt the encrypted string.
+    """
+
+    global padding_string
+
+    ciphertext = base64.b64decode(ciphertext)
+    iv = ciphertext[:AES.block_size]
+    cipher = AES.new(pad(key), AES.MODE_CFB, iv)
+    decrypted = cipher.decrypt(ciphertext[AES.block_size:])
+    l = decrypted.count(padding_string)
+
+    return decrypted[:len(decrypted)-l]
+
+
+def pad(str):
+    """Add padding to the key."""
+
+    global padding_string
+    str_len = len(str)
+
+    # Key must be maximum 32 bytes long, so take first 32 bytes
+    if str_len > 32:
+        return str[:32]
+
+    # If key size id 16, 24 or 32 bytes then padding not require
+    if str_len == 16 or str_len == 24 or str_len == 32:
+        return str
+
+    # Add padding to make key 32 bytes long
+    return str + ((32 - len(str) % 32) * padding_string)