adds CTRL-C handler and error messages to stderr

wpa-psk.diff

diff --git a/wpa-psk.py b/wpa-psk.py
index 0881ae3..9089caf 100644
--- a/wpa-psk.py
+++ b/wpa-psk.py
@@ -4,6 +4,12 @@ import sys
 from argparse import ArgumentParser
 from getpass import getpass
 from hashlib import pbkdf2_hmac
+from signal import signal, SIGINT
+
+def die(*_, **__):
+    sys.exit()
+
+signal = signal(SIGINT, die)
 
 iwd = """[Security]
 PreSharedKey={psk}"""
@@ -35,14 +41,14 @@ parser.add_argument(
 args = parser.parse_args()
 
 if not args.passphrase:
-    print("# reading passphrase from stdin")
+    print("# reading passphrase from stdin", file=sys.stderr)
     args.passphrase = getpass(prompt="")
 if not 8 <= len(args.passphrase) <= 63:
-    print("Passphrase must be 8..63 characters")
+    print("Passphrase must be 8..63 characters", file=sys.stderr)
     sys.exit(1)
 passphrase = args.passphrase.encode()
 if any(b < 32 or b == 127 for b in passphrase):
-    print("Invalid passphrase character")
+    print("Invalid passphrase character", file=sys.stderr)
     sys.exit(1)
 
 ssid = args.ssid.encode()