CURLOPT_ISSUERCERT_BLOB - issuer SSL certificate from memory blob

#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ISSUERCERT_BLOB,
                          struct curl_blob *stblob);

Pass a pointer to a curl_blob structure, which contains information (pointer and size) about a memory block with binary data of a CA certificate in PEM format. If the option is set, an additional check against the peer certificate is performed to verify the issuer is indeed the one associated with the certificate provided by the option. This additional check is useful in multi-level PKI where one needs to enforce that the peer certificate is from a specific branch of the tree.

This option should be used in combination with the CURLOPT_SSL_VERIFYPEER(3) option. Otherwise, the result of the check is not considered as failure.

A specific error code (CURLE_SSL_ISSUER_ERROR) is defined with the option, which is returned if the setup of the SSL/TLS session has failed due to a mismatch with the issuer of peer certificate (CURLOPT_SSL_VERIFYPEER(3) has to be set too for the check to fail).

If the blob is initialized with the flags member of struct curl_blob set to CURL_BLOB_COPY, the application does not have to keep the buffer around after setting this.

This option is an alternative to CURLOPT_ISSUERCERT(3) which instead expects a filename as input.


All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

This option works only with the following TLS backends: OpenSSL

extern char *certificateData;
extern size_t filesize;
int main(void)
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    struct curl_blob blob;
    curl_easy_setopt(curl, CURLOPT_URL, ""); = certificateData;
    blob.len = filesize;
    blob.flags = CURL_BLOB_COPY;
    curl_easy_setopt(curl, CURLOPT_ISSUERCERT_BLOB, &blob);
    res = curl_easy_perform(curl);

Added in 7.71.0. This option is supported by the OpenSSL backends.

Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.


2024-05-22 libcurl