---
name: "CURLOPT_SSLKEY_BLOB"
section: "3"
platform: "linux"
package: "curl"
version: "8.23.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_SSLKEY_BLOB"
---

# CURLOPT\_SSLKEY\_BLOB(3)

private key for client cert from memory blob

## NAME

CURLOPT\_SSLKEY\_BLOB - private key for client cert from memory blob

## SYNOPSIS

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

## DESCRIPTION

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)](/CURLOPT_SSLKEYTYPE/3.md)*.

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)](/CURLOPT_SSLKEY/3.md)* 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

## EXAMPLE

```
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);
  }
}
```

## AVAILABILITY

Added in curl 7.71.0

## RETURN VALUE

*[curl\_easy\_setopt(3)](/curl_easy_setopt/3.md)* returns a CURLcode indicating success or error.

CURLE\_OK (0) means everything was OK, non-zero means an error occurred, see *[libcurl-errors(3)](/libcurl-errors/3.md)*.

## SEE ALSO

[**CURLOPT\_SSLKEY**(3)](/CURLOPT_SSLKEY/3.md), [**CURLOPT\_SSLKEYTYPE**(3)](/CURLOPT_SSLKEYTYPE/3.md)