---
name: "CURLOPT_SSLENGINE"
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_SSLENGINE"
---

# CURLOPT\_SSLENGINE(3)

Set SSL engine or provider

## NAME

CURLOPT\_SSLENGINE - Set SSL engine or provider

## SYNOPSIS

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

## DESCRIPTION

Pass a pointer to a null-terminated string as parameter. It is used as the identifier for the *engine* or *provider* you want to use for your private key. OpenSSL 1 had engines, OpenSSL 3 has providers.

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

When asking libcurl to use a provider, the application can also optionally provide a *property*, a set of name value pairs. Such a property can be specified separated from the name with a colon (*:*).

Using this option multiple times makes the last set string override the previous ones. Set it to NULL to disable its use again.

## 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

```
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode result;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    curl_easy_setopt(curl, CURLOPT_SSLENGINE, "dynamic");
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}
```

## AVAILABILITY

Added in curl 7.9.3

## RETURN VALUE

CURLE\_OK - Engine found.

CURLE\_SSL\_ENGINE\_NOTFOUND - Engine not found, or OpenSSL was not built with engine support.

CURLE\_SSL\_ENGINE\_INITFAILED - Engine found but initialization failed.

CURLE\_NOT\_BUILT\_IN - Option not built in, OpenSSL is not the SSL backend.

CURLE\_UNKNOWN\_OPTION - Option not recognized.

CURLE\_OUT\_OF\_MEMORY - Insufficient heap space.

## SEE ALSO

[**CURLINFO\_SSL\_ENGINES**(3)](/CURLINFO_SSL_ENGINES/3.md), [**CURLOPT\_SSLENGINE\_DEFAULT**(3)](/CURLOPT_SSLENGINE_DEFAULT/3.md), [**CURLOPT\_SSLKEY**(3)](/CURLOPT_SSLKEY/3.md)