Added Windows & Linux backend for backup/restore.

Fixes #21

Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>

tools/secure_key/windows.py

@@ -0,0 +1,44 @@
+import sys
+import os
+import base64
+
+DOMAIN = "PicoKeys.com"
+USERNAME = "Pico-Fido"
+
+try:
+    import keyring
+except:
+    print('ERROR: keyring module not found! Install keyring package.\nTry with `pip install keyring`')
+    sys.exit(-1)
+
+try:
+    from cryptography.hazmat.primitives.serialization import Encoding, PrivateFormat, NoEncryption, load_pem_private_key
+    from cryptography.hazmat.primitives.asymmetric import ec
+except:
+    print('ERROR: cryptography module not found! Install cryptography package.\nTry with `pip install cryptography`')
+    sys.exit(-1)
+
+
+
+def generate_secure_key():
+    pkey = ec.generate_private_key(ec.SECP256R1())
+    set_secure_key(pkey)
+    return keyring.get_password(DOMAIN, USERNAME)
+
+def get_d(key):
+    return load_pem_private_key(key, password=None).private_numbers().private_value.to_bytes(32, 'big')
+
+def set_secure_key(pk):
+    try:
+        keyring.delete_password(DOMAIN, USERNAME)
+    except:
+        pass
+    keyring.set_password(DOMAIN, USERNAME, pk.private_bytes(Encoding.PEM, PrivateFormat.PKCS8, NoEncryption()).decode())
+
+def get_secure_key():
+    key = None
+    try:
+        key = keyring.get_password(DOMAIN, USERNAME)
+    except keyring.errors.KeyringError:
+        key = generate_secure_key()
+    return get_d(key.encode())