use File::Slurp qw(read_file); use MIME::Base64 qw(encode_base64); require Crypt::OpenSSL::RSA; my $key_text = read_file( $key_filename ); my $rsa_key = Crypt::OpenSSL::RSA->new_private_key($key_text); $rsa_key->use_pkcs1_padding(); my $bin_signature = $rsa_key->sign($plaintext); print encode_base64($bin_signature, '');