You can use also Math::GMPz, which uses GMP library: 

use 5.012;
use warnings;
use Math::GMPz qw(:mpz );
use Digest::SHA qw(sha512_hex);

my $sha = sha512_hex('password');
my $op = Rmpz_init_set_str($sha, 16);
my $rop = Rmpz_init2(512);
Rmpz_nextprime($rop, $op);
say Rmpz_get_str($rop, 16);

[download]
it takes less than a second on my notebook.

In reply to Re^3: Generate RSA keypair in perl efficently with custom PRNG by zwon
in thread Generate RSA keypair in perl efficently with custom PRNG by sebastiannielsen

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