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---
c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_SSH_HOSTKEYFUNCTION
Section: 3
Source: libcurl
See-also:
- CURLOPT_SSH_HOSTKEYDATA (3)
- CURLOPT_SSH_KNOWNHOSTS (3)
---
# NAME
CURLOPT_SSH_HOSTKEYFUNCTION - callback to check host key
# SYNOPSIS
~~~c
#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).
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).
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
~~~c
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.
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