perl SHA HMAC message digestion digital signature

use strict;
use Digest::HMAC_SHA1;


my $key="This is the secret key";
my $input="Good Evening";

my $hmac=new Digest::HMAC_SHA1($key);

$hmac->add($input);

my $digest=$hmac->b64digest();
print "key:$key, input:$input, digest:$digest\n";
#output: key:This is the secret key, input:Good Evening, digest:kRfi1C7Q64oHS+6hEX2BnYB/tnc