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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, $key);
}
# make a usable number out of that HMAC result
sub hotp_truncate {
my ($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 $truncate;
}
# TOTP is HOTP(K,c) where counter c is time based and changed every x seconds (30 here)
sub totp {
my ($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 $otp;
}
# basically HMAC(key, counter)
sub hotp {
my ($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);
# run trunc to generate a user useable number
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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