Tribblix: manual page: CURLOPT_SSL

CURLOPT_SSL_VERIFYPEER(3) Introduction to Library Functions

NAME

CURLOPT_SSL_VERIFYPEER - verify the peer's SSL certificate

SYNOPSIS

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_VERIFYPEER, long verify);

DESCRIPTION

Pass a long as parameter to enable or disable.

This option determines whether curl verifies the authenticity of the
peer's certificate. A value of 1 means curl verifies; 0 (zero) means
it does not.

When negotiating a TLS or SSL connection, the server sends a
certificate indicating its identity. curl verifies whether the
certificate is authentic, i.e. that you can trust that the server is
who the certificate says it is. This trust is based on a chain of
digital signatures, rooted in certification authority (CA)
certificates you supply. curl uses a default bundle of CA
certificates (the path for that is determined at build time) and you
can specify alternate certificates with the CURLOPT_CAINFO(3) option
or the CURLOPT_CAPATH(3) option.

When CURLOPT_SSL_VERIFYPEER(3) is enabled, and the verification fails
to prove that the certificate is signed by a CA, the connection
fails.

When this option is disabled (set to zero), the CA certificates are
not loaded and the peer certificate verification is simply skipped.

Authenticating the certificate is not enough to be sure about the
server. You typically also want to ensure that the server is the
server you mean to be talking to. Use CURLOPT_SSL_VERIFYHOST(3) for
that. The check that the host name in the certificate is valid for
the hostname you are connecting to is done independently of the
CURLOPT_SSL_VERIFYPEER(3) option.

WARNING: disabling verification of the certificate allows bad guys to
man-in-the-middle the communication without you knowing it. Disabling
verification makes the communication insecure. Just having encryption
on a transfer is not enough as you cannot be sure that you are
communicating with the correct end-point.

When libcurl uses secure protocols it trusts responses and allows for
example HSTS and Alt-Svc information to be stored and used
subsequently. Disabling certificate verification can make libcurl
trust and use such information from malicious servers.

DEFAULT

1 - enabled

PROTOCOLS

This functionality affects all TLS based protocols: HTTPS, FTPS,
IMAPS, POP3S, SMTPS etc.

All TLS backends support this option.

EXAMPLE

int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

/* Set the default value: strict certificate check please */
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 1L);

curl_easy_perform(curl);
}
}

AVAILABILITY

Added in curl 7.4.2

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).