---
name: "CURLOPT_SSH_HOSTKEYFUNCTION"
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_SSH_HOSTKEYFUNCTION"
---

# CURLOPT\_SSH\_HOSTKEYFUNCTION(3)

callback to check host key

## NAME

CURLOPT\_SSH\_HOSTKEYFUNCTION - callback to check host key

## SYNOPSIS

```
#include <curl/curl.h>
int keycallback(void *clientp,
                int keytype,
                const char *key,
                size_t keylen);
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSH_HOSTKEYFUNCTION,
                          keycallback);
```

## DESCRIPTION

Pass a pointer to your callback function, which should match the prototype shown above. It overrides *[CURLOPT\_SSH\_KNOWNHOSTS(3)](/CURLOPT_SSH_KNOWNHOSTS/3.md)*.

This callback gets called when the verification of the SSH host key is needed.

**key** is **keylen** bytes long and is the key to check. **keytype** says what type it is, from the **CURLKHTYPE\_**\* series in the **curl\_khtype** enum.

**clientp** is a custom pointer set with *[CURLOPT\_SSH\_HOSTKEYDATA(3)](/CURLOPT_SSH_HOSTKEYDATA/3.md)*.

The callback MUST return one of the following return codes to tell libcurl how to act:

- CURLKHMATCH\_OK

  The host key is accepted, the connection should continue.

- CURLKHMATCH\_MISMATCH

  the host key is rejected, the connection is canceled.

## DEFAULT

NULL

## PROTOCOLS

SCP and SFTP

## EXAMPLE

```
struct mine {
  void *custom;
};
int hostkeycb(void *clientp,    /* passed with CURLOPT_SSH_HOSTKEYDATA */
              int keytype,      /* CURLKHTYPE */
              const char *key,  /* host key to check */
              size_t keylen)    /* length of the key */
{
  /* 'clientp' points to the callback_data struct */
  /* investigate the situation and return the correct value */
  return CURLKHMATCH_OK;
}
int main(void)
{
  struct mine callback_data;
  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "sftp://example.com/thisfile.txt");
    curl_easy_setopt(curl, CURLOPT_SSH_HOSTKEYFUNCTION, hostkeycb);
    curl_easy_setopt(curl, CURLOPT_SSH_HOSTKEYDATA, &callback_data);
    curl_easy_perform(curl);
  }
}
```

## AVAILABILITY

Added in 7.84.0 , work only with libssh2 backend.

## RETURN VALUE

Returns CURLE\_OK if the option is supported, and CURLE\_UNKNOWN\_OPTION if not.

## SEE ALSO

[**CURLOPT\_SSH\_HOSTKEYDATA**(3)](/CURLOPT_SSH_HOSTKEYDATA/3.md), [**CURLOPT\_SSH\_KNOWNHOSTS**(3)](/CURLOPT_SSH_KNOWNHOSTS/3.md)