my $rsa = Crypt::OpenSSL::RSA->generate_key(2048); # or
my $rsa_priv = Crypt::OpenSSL::RSA->new_private_key($rsa->get_private_key_string() );
my $rsa_pub = Crypt::OpenSSL::RSA->new_public_key( $rsa->get_public_key_string() );

my $ciphertext = $rsa_pub->encrypt($plaintext) ;