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-rw-r--r--encrypt.py95
1 files changed, 95 insertions, 0 deletions
diff --git a/encrypt.py b/encrypt.py
new file mode 100644
index 0000000..9809d45
--- /dev/null
+++ b/encrypt.py
@@ -0,0 +1,95 @@
+#!/usr/bin/env python3
+
+import secrets
+from Cryptodome.Cipher import AES
+import base64
+import struct
+import subprocess
+import binascii
+
+def _pad(data, blocksize):
+ return (data + b'\x80' + b'\x00'*blocksize)[:blocksize]
+
+def _unpad(data):
+ data = data.rstrip(b'\0')
+ if data[-1] == 0x80:
+ return data[:-1]
+ else:
+ raise ValueError('Invalid padding!')
+
+def encrypt_file(filename_in):
+ file_id = secrets.token_urlsafe(22)
+ auth_secret = secrets.token_bytes(16)
+ key = secrets.token_bytes(16)
+ cipher_nonce = secrets.token_bytes(8)
+
+ token_cipher = AES.new(auth_secret, AES.MODE_GCM)
+ ciphertext, token_tag = token_cipher.encrypt_and_digest(key)
+ token = base64.b64encode(ciphertext)
+
+ with open(filename_in, 'rb', buffering=8192) as fin, open(f'{file_id}.enc', 'wb', buffering=8192) as fout:
+ fout.write(token_cipher.nonce) # 16 bytes
+ fout.write(token_tag) # 16 bytes
+ fout.write(auth_secret) # 16 bytes
+ fout.write(cipher_nonce) # 8 bytes
+
+ subprocess.check_call(['openssl', 'enc', '-aes-128-ctr',
+ '-K', binascii.hexlify(key),
+ '-iv', binascii.hexlify(cipher_nonce + '\0'*8)
+
+ data = fin.read(cipher.block_size) or None
+ while data is not None:
+ next_data = fin.read(cipher.block_size) or None
+ if not next_data: # padding required
+ if len(data) == cipher.block_size:
+ next_data = b''
+ else:
+ data = _pad(data, cipher.block_size)
+ fout.write(cipher.encrypt(data))
+ data = next_data
+
+ return file_id, token
+
+def decrypt_generator(file_id, token, seek=0):
+
+ with open(f'{file_id}.enc', 'rb', buffering=8192) as fin:
+ token_nonce = fin.read(16)
+ token_tag = fin.read(16)
+ auth_secret = fin.read(16)
+ data_nonce = fin.read(8)
+
+ ciphertext = base64.b64decode(token)
+ token_cipher = AES.new(auth_secret, AES.MODE_GCM, nonce=token_nonce)
+ key = token_cipher.decrypt_and_verify(ciphertext, token_tag)
+
+ # Use token cipher's block size assuming the two are the same
+ cipher = AES.new(key, AES.MODE_CTR,
+ initial_value=struct.pack('<Q', seek // token_cipher.block_size), nonce=data_nonce)
+ fin.seek(seek - seek % cipher.block_size, 1)
+ offset = seek % cipher.block_size
+
+ next_block = fin.read(cipher.block_size)
+ while next_block:
+ block = next_block
+ next_block = fin.read(cipher.block_size)
+ data = cipher.decrypt(block)
+
+ if not next_block: # remove padding
+ data = _unpad(data)
+
+ yield data[offset:]
+ offset = 0
+
+if __name__ == '__main__':
+ import argparse
+ parser = argparse.ArgumentParser()
+ parser.add_argument('infile')
+ parser.add_argument('outfile')
+ args = parser.parse_args()
+
+ file_id, token = encrypt_file(args.infile)
+
+ with open(args.outfile, 'wb', buffering=8192) as fout:
+ for data in decrypt_generator(file_id, token):
+ fout.write(data)
+