如何在C 中使用OpenSSL创建OCSP请求

想要您尝试做的是为openssl ocsp命令生成C 代码：

openssl ocsp -issuer issuer.pem -cert alice.pem -cert bob.pem -reqout -reqout ocspreq.der

您需要的主要OpenSSL API是：

• pem_read_bio_x509-阅读证书
• ocsp_request_new-生成OCSP请求
• ocsp_request_add0_id-添加证书
• i2d_ocsp_request_bio-以der格式写出请求

使用的API可能会根据您希望阅读并写出的证书格式而有所不同。

上述openssl命令中的一个示例以简单的C 代码为：

template<typename T, typename D>
std::unique_ptr<T, D> make_handle(T* handle, D deleter)
{
    return std::unique_ptr<T, D>{handle, deleter};
}
bool generate_ocsp_request()
{
    // load issuer certificate
    auto file = make_handle(BIO_new_file("issuer.pem", "r"), BIO_free);
    if(!file) return false;
    auto const issuer = make_handle(PEM_read_bio_X509(file.get(), nullptr, nullptr, nullptr), X509_free);
    if(!issuer) return false;
    // setup OCSP request
    auto const request = make_handle(OCSP_REQUEST_new(), OCSP_REQUEST_free);
    if(!request) return false;
    auto const cert_id_md = EVP_sha1();
    // add alice certificate to OCSP request
    file = make_handle(BIO_new_file("alice.pem", "r"), BIO_free);
    if(!file) return false;
    auto cert = PEM_read_bio_X509(file.get(), nullptr, nullptr, nullptr);
    auto id = OCSP_cert_to_id(cert_id_md, cert, issuer.get());
    if (id == nullptr) return false;
    if (!OCSP_request_add0_id(request.get(), id)) return false;
    // add bob certificate to OCSP request
    file = make_handle(BIO_new_file("bob.pem", "r"), BIO_free);
    if(!file) return false;
    cert = PEM_read_bio_X509(file.get(), nullptr, nullptr, nullptr);
    id = OCSP_cert_to_id(cert_id_md, cert, issuer.get());
    if (id == nullptr) return false;
    if (!OCSP_request_add0_id(request.get(), id)) return false;
    // write the request out in DER format
    file = make_handle(BIO_new_file("ocspreq.der", "wb"), BIO_free);
    if(!file) return false;
    // the below doesn't compile in C++ :(
    // return i2d_OCSP_REQUEST_bio(file.get(), request.get()) != 0;
    // go around the macro's that cause the problem in C++ because it will not automatically convert void* to unsigned char* like in C
    return ASN1_i2d_bio(reinterpret_cast<i2d_of_void *>(i2d_OCSP_REQUEST), file.get(), reinterpret_cast<unsigned char*>(request.get())) != 0;
}

更新：

阅读响应有点参与。

用于处理响应的主要API是：

• d2i_ocsp_response_bio- der格式的加载响应
• ocsp_response_get1_basic-提取响应信息
• ocsp_check_nonce-检查响应是为请求(可选(
• ocsp_basic_verify-验证响应有效(可选(

没有可以提取的"文本"，您需要从响应中特别提取您想要的内容。

以下代码是此命令的一个示例

openssl ocsp -respin ocspresp.der -reqin ocspreq.der -issuer ISSUER.PEM -CERT ALICE.PEM -CERT BOB.PEM

bool read_ocsp_response()
{
    // load ocsp request (der format)
    auto file = make_handle(BIO_new_file("ocspreq.der", "rb"), BIO_free);
    if(!file) return false;
    auto const request = make_handle(d2i_OCSP_REQUEST_bio(file.get(), nullptr), OCSP_REQUEST_free);
    if(!request) return false;
    // load ocsp response (der format)
    file = make_handle(BIO_new_file("ocspresp.der", "rb"), BIO_free);
    if(!file) return false;
    auto const response = make_handle(d2i_OCSP_RESPONSE_bio(file.get(), nullptr), OCSP_RESPONSE_free);
    if(!response) return false;
    file.reset();
    // was the server response ok?
    if(OCSP_response_status(response.get()) != OCSP_RESPONSE_STATUS_SUCCESSFUL) return false;
    // verify response
    auto const basic_response = make_handle(OCSP_response_get1_basic(response.get()), OCSP_BASICRESP_free);
    if(!basic_response) return false;
    // check that the response is for the expected request
    auto const nonce_check_result = OCSP_check_nonce(request.get(), basic_response.get());
    if(nonce_check_result <= 0)
    {
        if(nonce_check_result == -1)
        {
            puts("WARNING: no nonce in response");
        }
        else
        {
            return false;
        }
    }
    // verify the response against the issuer certificate
    auto const issuers_certificate_stack = make_handle(sk_X509_new_null(), [](auto handle){ sk_X509_pop_free(handle, X509_free); });
    if(!issuers_certificate_stack) return false;
    file = make_handle(BIO_new_file("issuer.pem", "r"), BIO_free);
    if(!file) return false;
    auto const issuer = PEM_read_bio_X509(file.get(), nullptr, nullptr, nullptr);
    if(!issuer) return false;
    file.reset();
    sk_X509_push(issuers_certificate_stack.get(), issuer);
    // load default certificate store
    auto const store = make_handle(X509_STORE_new(), X509_STORE_free);
    if(!store) return false;
    auto const lookup = X509_STORE_add_lookup(store.get(), X509_LOOKUP_file());
    if(lookup == nullptr) return false;
    if(OCSP_basic_verify(basic_response.get(), issuers_certificate_stack.get(), store.get(), OCSP_TRUSTOTHER) != 1) return false;
    // check that all the certificates have a status ok results
    if(OCSP_resp_count(basic_response.get() == 0) return false;
    for (auto i = 0; i < OCSP_resp_count(basic_response.get()); i++)
    {
        auto const single_response = OCSP_resp_get0(basic_response.get(), i);
        if(single_response == nullptr) return false;
        if(OCSP_single_get0_status(single_response, nullptr, nullptr, nullptr, nullptr) != V_OCSP_CERTSTATUS_GOOD) return false;
    }
    return true;
}

如果要查找诸如alice.pem之类的特定证书的状态，则使用从ocsp_cert_to_id返回的ocsp_certid(请参阅生成请求(，然后将其与ocsp_resp_find_status api一起使用，以查找该证书的状态，而不是枚举所有证书就像我在上面的代码中所做的一样。

如果您要定期查询证书，则可能想使用从状态返回的下一个更新时间邮票，以进行下一个检查呼叫。