From 8e624684ab3c3db83febcb2d76be208a96f234da Mon Sep 17 00:00:00 2001
From: Calvin Morrison <calvin@fastmailteam.com>
Date: Tue, 16 Oct 2018 09:55:28 -0400
Subject: add working totp.pl

---
 totp.pl | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 totp.pl

diff --git a/totp.pl b/totp.pl
new file mode 100644
index 0000000..21a0c00
--- /dev/null
+++ b/totp.pl
@@ -0,0 +1,75 @@
+use MIME::Base32;
+use POSIX ;
+use Digest::SHA;
+use v5.14;
+
+# take a string, make it a hex and run HMAC on it
+sub  hmac_sha1_hex_string {
+	my ($data, $key) = map pack('H*', $_), @_;
+	return Digest::SHA::hmac_sha1_hex($data, $key);
+}
+
+# everything is 2 here because we are looking at the byte level.. probably
+# should just convert this into a byte array but I'm a noob
+sub hotp_truncate {
+	my ($hex) = @_;
+	my $lastbyte= substr $hex, -2;
+	my $offset = (hex $lastbyte) & 0xf;
+	my $offset = $offset * 2;
+
+	my $truncate =	( 
+		(hex substr($hex, $offset    , 2) & 0x7f) << 24 | 
+		(hex substr($hex, $offset + 2, 2) & 0xff) << 16 | 
+		(hex substr($hex, $offset + 4, 2) & 0xff) << 8 | 
+		(hex substr($hex, $offset + 6, 2) & 0xff) 
+	);
+
+  # 6 letter;
+	$truncate = substr($truncate, -6);
+
+	return $truncate;
+}
+
+# TOTP is HOTP(K,c) where counter c is time based and changed every 30 seconds (here)
+# HOTP
+sub totp {
+	my ($time, $secret) = @_;
+
+	# definition for otp(K,c) where c is the counter -> with totp, we use time / 30
+	$time = floor($time / 30);
+
+	# do the work
+	my $otp = hotp($time, $secret);
+
+	return $otp;
+}
+sub hotp {
+	my ($time, $secret) = @_;
+
+	my $secret_hex = unpack "H*", decode_base32($secret);
+	my $time_hex= sprintf("%016s", sprintf("%x", $time));
+
+
+	# SHA-1 Hex your secret 
+	my $hash = hmac_sha1_hex_string($time_hex, $secret_hex);
+
+	my $otp = hotp_truncate($hash);
+
+	return $otp;
+
+}
+
+my $secret = "";
+if($#ARGV != 0)  {
+	$secret = <STDIN>;
+	chomp $secret;
+} else {
+	$secret = $ARGV[0] ;
+}
+
+my $starttime = time;
+
+my $otp = totp($starttime, $secret);
+
+printf("%ds left: %06d, in your clipboard\n", 30 - $starttime % 30, $otp);
+system("echo $otp | xclip /dev/stdin");
-- 
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