add user credentials file and tool

Author: julienschmidt

README.md

@@ -17,6 +17,11 @@ See `scsync --help` for all options.
 ### Server:
 `scsync [-s] [-p <port>] [-f <directory-path>]`
 
+#### User Credentials
+For each user a password hash and salt have to be generated using the `tools/gen_user_vkey.py` script.
+
+The credentials are then stored as CSV using the format `<username>,<salt>,<verification_key>` in the `users.csv`.
+
 ### Arguments:
 `-s` Server mode: accept incoming connections from any host
 `-p` Specify the port number (default: `5000`)

requirements.txt

@@ -1,3 +1,5 @@
 aiofiles>=0.3
+cryptography>=1.8
+srp>=1.0
 watchdog>=0.8
 pyrsync2>=0.2

tools/gen_user_vkey.py

@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+# coding: utf-8
+
+import base64
+
+import srp
+
+
+def main():
+    username = input("Enter username: ")
+    password = input("Enter password: ")
+    salt, vkey = srp.create_salted_verification_key(username, password)
+
+    print()
+    print("Add the following line to the users.csv:")
+    print()
+    print("%s,%s,%s" % (username, base64.b64encode(salt).decode(
+        'utf-8'), base64.b64encode(vkey).decode('utf-8')))
+
+if __name__ == "__main__":
+    main()