Added crypto.py: Contains function that encrypt data and decrypt ciphers using AES.

Functions defined: pad, encrypt, decrypt, encrypt_shards, decrypt_shards.

Also added: tests/test_crypto.py

2 files changed, 136 insertions, 0 deletions

diff --git a/combox/crypto.py b/combox/crypto.py
new file mode 100644
index 0000000..3f17cc0
--- /dev/null
+++ b/combox/crypto.py
@@ -0,0 +1,84 @@
+#    Copyright (C) 2014 Combox author(s). See AUTHORS.
+#
+#    This file is part of Combox.
+#
+#   Combox 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.
+#
+#   Combox 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 Combox (see COPYING).  If not, see
+#   <http://www.gnu.org/licenses/>.
+
+## Adapted from https://gist.github.com/sekondus/4322469
+
+import base64
+import os
+
+from Crypto.Cipher import AES
+
+BLOCK_SIZE = 32
+PAD_CHAR = '#'
+
+
+def pad(data):
+    """Pad data such that its length is a multiple of BLOCK_SIZE.
+    """
+
+    padding = (BLOCK_SIZE - (len(data) % BLOCK_SIZE)) * PAD_CHAR
+    data += padding
+
+    return data
+
+
+def encrypt(data, secret):
+    """Encrypt byestream and return cipher.
+    """
+    aes = AES.new(pad(secret))
+    cipher = base64.b64encode(aes.encrypt(pad(data)))
+    
+    return cipher
+
+
+def decrypt(cipher, secret):
+    """Decrypt cipher and return data.
+    """
+    aes = AES.new(pad(secret))
+    data = aes.decrypt(base64.b64decode(cipher)).rstrip(PAD_CHAR)
+
+    return data
+
+def encrypt_shards(shards, secret):
+    """Encrypt the shards of data and return a list of ciphers.
+
+    shards: list of shards (string, bytes).
+    secret: top secret passphrase
+    """
+
+    ciphers = []
+    for shard in shards:
+        cipher = encrypt(shard, secret)
+        ciphers.append(cipher)
+
+    return ciphers
+
+
+def decrypt_shards(ciphers, secret):
+    """Decrypt the ciphered shards and return a list of shards.
+
+    shards: list of ciphered shards.
+    secret: top secret passphrase
+    """
+
+    shards = []
+    for cipher in ciphers:
+        shard = decrypt(cipher, secret)
+        shards.append(shard)
+
+    return shards
diff --git a/combox/tests/test_crypto.py b/combox/tests/test_crypto.py
new file mode 100644
index 0000000..143cfdb
--- /dev/null
+++ b/combox/tests/test_crypto.py
@@ -0,0 +1,52 @@
+#    Copyright (C) 2014 Combox author(s). See AUTHORS.
+#
+#    This file is part of Combox.
+#
+#   Combox 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.
+#
+#   Combox 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 Combox (see COPYING).  If not, see
+#   <http://www.gnu.org/licenses/>.
+
+from os import path
+
+from file import (split_data, glue_data, write_file,
+                  read_file, write_shards, read_shards)
+from crypto import encrypt, decrypt, encrypt_shards, decrypt_shards
+
+PASS = 'topsecret'
+### Read file, encrypt it to a cipher, write cipher to file, read
+### encrypted file, decrypt it, write decrypted data to file.
+f = path.abspath('tests/files/the-red-star.jpg')
+f_content = read_file(f)
+f_cipher = encrypt(f_content, PASS)
+f_encrypted = path.abspath('tests/files/the-red-star.cipher')
+write_file(f_encrypted, f_cipher)
+f_cipher = read_file(f_encrypted)
+f_content = decrypt(f_cipher, PASS)
+f = path.abspath('tests/files/the-red-star-decrypted.jpg')
+write_file(f, f_content)
+
+### Read file, split it, encrypt shards, write encrypted shards to
+### file, read encrypted shards from file, decrypt the encrypted
+### shards, glue the shards together, write glued data to file.
+f = path.abspath('tests/files/the-red-star.jpg')
+f_content = read_file(f)
+f_shards = split_data(f_content, 5)
+ciphered_shards = encrypt_shards(f_shards, PASS)
+f_path = path.dirname(f)
+f_basename = "%s.ciphered" % path.basename(f)
+write_shards(ciphered_shards, f_path, f_basename)
+ciphered_shards = read_shards(f_path, f_basename)
+f_parts = decrypt_shards(ciphered_shards, PASS)
+f_content = glue_data(f_parts)
+f = path.abspath('tests/files/the-red-star-from-ciphered-shards.jpg')
+write_file(f, f_content)