CURLOPT_ISSUERCERT_BLOB(3) Library Functions Manual
NAME
CURLOPT_ISSUERCERT_BLOB - issuer SSL certificate from memory blob
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ISSUERCERT_BLOB,
struct curl_blob *stblob);
DESCRIPTION
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.
The provided issuer certificate is used only for an issuer check against
the peer certificate; it is not validated or trusted by itself.
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
(C) 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.
DEFAULT
NULL
PROTOCOLS
This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS,
POP3S, SMTPS etc. only
This option works only with the following TLS backends: OpenSSL
EXAMPLE
extern char *certificateData;
extern size_t filesize;
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode result;
struct curl_blob blob;
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
blob.data = certificateData;
blob.len = filesize;
blob.flags = CURL_BLOB_COPY;
curl_easy_setopt(curl, CURLOPT_ISSUERCERT_BLOB, &blob);
result = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
AVAILABILITY
Added in curl 7.71.0
RETURN VALUE
curl_easy_setopt(3) returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non-zero means an error occurred,
see libcurl-errors(3).
SEE ALSO
CURLOPT_CRLFILE(3), CURLOPT_ISSUERCERT(3), CURLOPT_SSL_VERIFYHOST(3),
CURLOPT_SSL_VERIFYPEER(3)
libcurl 2026-10-18 CURLOPT_ISSUERCERT_BLOB(3)
curl 8.23.0 - Generated Sun Oct 18 16:02:01 CDT 2026