OpenSSL::PKey::DSA#to_s

static VALUE
ossl_dsa_export(int argc, VALUE *argv, VALUE self)
{
    DSA *dsa;
    BIO *out;
    const EVP_CIPHER *ciph = NULL;
    VALUE cipher, pass, str;

    GetDSA(self, dsa);
    rb_scan_args(argc, argv, "02", &cipher, &pass);
    if (!NIL_P(cipher)) {
        ciph = ossl_evp_get_cipherbyname(cipher);
        pass = ossl_pem_passwd_value(pass);
    }
    if (!(out = BIO_new(BIO_s_mem()))) {
        ossl_raise(eDSAError, NULL);
    }
    if (DSA_HAS_PRIVATE(dsa)) {
        if (!PEM_write_bio_DSAPrivateKey(out, dsa, ciph, NULL, 0,
                                         ossl_pem_passwd_cb, (void *)pass)){
            BIO_free(out);
            ossl_raise(eDSAError, NULL);
        }
    } else {
        if (!PEM_write_bio_DSA_PUBKEY(out, dsa)) {
            BIO_free(out);
            ossl_raise(eDSAError, NULL);
        }
    }
    str = ossl_membio2str(out);

    return str;
}