---
name: "CURLOPT_SSLKEYTYPE"
section: "3"
platform: "macos"
package: "curl"
version: "166.0.0.0.1"
release: "macOS 26.5"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_SSLKEYTYPE"
---

# CURLOPT\_SSLKEYTYPE(3)

type of the private key file

## NAME

CURLOPT\_SSLKEYTYPE - type of the private key file

## SYNOPSIS

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSLKEYTYPE, char *type);
```

## DESCRIPTION

Pass a pointer to a null-terminated string as parameter. The string should be the format of your private key. Supported formats are "PEM", "DER" and "ENG".

The format "ENG" enables you to load the private key from a crypto engine. In this case *[CURLOPT\_SSLKEY(3)](/CURLOPT_SSLKEY/3.md)* is used as an identifier passed to the engine. You have to set the crypto engine with *[CURLOPT\_SSLENGINE(3)](/CURLOPT_SSLENGINE/3.md)*. "DER" format key file currently does not work because of a bug in OpenSSL.

The application does not have to keep the string around after setting this option.

## DEFAULT

"PEM"

## PROTOCOLS

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

## EXAMPLE

```
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    curl_easy_setopt(curl, CURLOPT_SSLCERT, "client.pem");
    curl_easy_setopt(curl, CURLOPT_SSLKEY, "key.pem");
    curl_easy_setopt(curl, CURLOPT_SSLKEYTYPE, "PEM");
    curl_easy_setopt(curl, CURLOPT_KEYPASSWD, "s3cret");
    res = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}
```

## AVAILABILITY

If built TLS enabled.

## RETURN VALUE

Returns CURLE\_OK if TLS is supported, CURLE\_UNKNOWN\_OPTION if not, or CURLE\_OUT\_OF\_MEMORY if there was insufficient heap space.

## SEE ALSO

[**CURLOPT\_PROXY\_SSLKEYTYPE**(3)](/CURLOPT_PROXY_SSLKEYTYPE/3.md), [**CURLOPT\_SSLCERT**(3)](/CURLOPT_SSLCERT/3.md), [**CURLOPT\_SSLKEY**(3)](/CURLOPT_SSLKEY/3.md)