I ran into this when we updated to CentOS 7.2 and went from perl 5.10 to 5.16. $p is too big for perl to subtract 1 from and results in inf. Still trying to figure out why it worked before but for now using Math::BigInt to calculate p_minus1 will fix it:

sub gen_k {
    my ($p) = @_;

    ## XXX choose bitsize based on bitsize of $p
    my $bits     = 198;
    my $p_minus1 = Math::BigInt->new($p)->bsub(1);

    my $k = Crypt::OpenPGP::Util::get_random_bigint($bits);

    while (1) {
        last if Math::BigInt::bgcd($k, $p_minus1) == 1;
        $k++;
    }
    $k;
}
[download]