CURLOPT_SSLKEY_BLOB(3)

CURLOPT_SSLKEY_BLOB3

Private key for client cert from memory blob

Usage

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

Overview

Pass a pointer to a curl_blob structure, which contains information (pointer and size) for a private key. Compatible with OpenSSL and Rustls. The format (like "PEM") must be specified with CURLOPT_SSLKEYTYPE(3).

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_SSLKEY(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, Rustls and wolfSSL

Examples

extern char *certificateData; /* point to cert */
extern size_t filesize; /* size of cert */
extern char *privateKeyData; /* point to key */
extern size_t privateKeySize; /* size of key */
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_SSLCERT_BLOB, &blob);
    curl_easy_setopt(curl, CURLOPT_SSLCERTTYPE, "PEM");
    blob.data = privateKeyData;
    blob.len = privateKeySize;
    curl_easy_setopt(curl, CURLOPT_SSLKEY_BLOB, &blob);
    curl_easy_setopt(curl, CURLOPT_KEYPASSWD, "s3cret");
    curl_easy_setopt(curl, CURLOPT_SSLKEYTYPE, "PEM");
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

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).

Releases

4 releases since Debian 11 (Bullseye); the text changed 3 times.

  1. 11
  2. 12
  3. 13
  4. Arch

Availability

Added in curl 7.71.0

From curl 8.23.0-1 in Arch Linux 2026-11-01. Parsed by carta from the page's man source.