CURLOPT_SSH_HOST_PUBLIC_KEY_MD5(3) Library Functions Manual
NAME
CURLOPT_SSH_HOST_PUBLIC_KEY_MD5 - MD5 checksum of SSH server public key
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSH_HOST_PUBLIC_KEY_MD5,
char *md5);
DESCRIPTION
Pass a char pointer pointing to a string containing 32 hexadecimal
digits. The string should be the 128-bit MD5 checksum of the remote
host's public key, and libcurl aborts the connection to the host unless
the MD5 checksum match.
MD5 is a weak algorithm. We strongly recommend using
CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256(3) instead.
The application does not have to keep the string around after setting
this option.
Using this option multiple times makes the last set string override the
previous ones. Set it to NULL to disable its use again.
This option is only applied when libcurl creates a new SSH connection.
Once a connection has been created and successfully verified with this
MD5 check, it is deemed vetted and may be reused by libcurl without
performing the MD5 verification again, even if you later change or
disable this option or switch to other verification mechanisms such as
CURLOPT_SSH_KNOWNHOSTS(3) or CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256(3). Any
such changes only affect future new connections, not already
established ones.
When MD5 verification is enabled for a connection via this option,
libcurl uses that MD5-based check instead of the known hosts/host key
callback verification path for that connection, so you must not assume
that both the MD5 check and the known hosts/host key callback
verification are performed for the same connection.
DEFAULT
NULL
PROTOCOLS
This functionality affects scp and sftp
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode result;
curl_easy_setopt(curl, CURLOPT_URL, "sftp://example.com/file");
curl_easy_setopt(curl, CURLOPT_SSH_HOST_PUBLIC_KEY_MD5,
"afe17cd62a0f3b61f1ab9cb22ba269a7");
result = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
AVAILABILITY
Added in curl 7.17.1
RETURN VALUE
curl_easy_setopt(3) returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non-zero means an error occurred,
see libcurl-errors(3).
SEE ALSO
CURLOPT_SSH_AUTH_TYPES(3), CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256(3),
CURLOPT_SSH_KNOWNHOSTS(3), CURLOPT_SSH_PUBLIC_KEYFILE(3)
libcurl 2026-06-09
CURLOPT_SSH_HOST_PUBLIC_KEY_MD5(3)
curl 8.20.0 - Generated Wed Jun 10 08:06:19 CDT 2026