add xor.py

Author: mmktomato

README.md

@@ -1,2 +1,16 @@
 # python-xor-cipher
-File encryption with XOR-Cipher in Python
+File encryption with XOR-Cipher in Python.
+
+## Usage
+
+```
+$ python3 xor.py <infile> <outfile>
+
+or
+
+$ python3 xor.py <infile> <outfile> --key <password>
+```
+
+* /infile/ is a file path to be encrypted.
+* /outfile/ is a encrypted file path.
+* /password/ is a encryption password.

xor.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+
+import sys
+import argparse
+from getpass import getpass
+from pathlib import Path
+from hashlib import sha256
+
+def get_seed(key):
+    return sha256(key.encode('utf-8')).digest()
+
+def parse_args():
+    parser = argparse.ArgumentParser(description='XOR cipher')
+    parser.add_argument('infile', help='input file path')
+    parser.add_argument('outfile', help='output file path')
+    parser.add_argument('--key', help='encryption password')
+
+    args = parser.parse_args()
+
+    if args.key is None:
+        key = getpass()
+    else:
+        key = args.key
+
+    return (Path(args.infile), Path(args.outfile), key)
+
+def validate_args(infile, outfile, seed):
+    if not infile.is_file():
+        sys.exit('"{}" is not a file.'.format(infile))
+
+    if infile.stat().st_size < len(seed):
+        sys.exit('infile must be larger than {} bytes.'.format(len(seed)))
+
+    if outfile.is_file():
+        sys.exit('"{}" is already exists.'.format(outfile))
+
+if __name__ == '__main__':
+    (infile, outfile, key) = parse_args()
+    seed = get_seed(key)
+    validate_args(infile, outfile, seed)
+
+    with infile.open('rb') as f_in:
+        with outfile.open('wb') as f_out:
+            i = 0
+            while f_in.peek():
+                c = ord(f_in.read(1))
+                j = i % len(seed)
+                b = bytes([c ^ seed[j]])
+                f_out.write(b)
+                i = i + 1
+