Ubuntu Manpage: CURLOPT_SSL_VERIFYPEER - verify the peer's SSL certificate

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 authentic, the connection fails. When the option is zero, the peer
certificate verification succeeds regardless.

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 host name 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.

NOTE: even when this option is disabled, depending on the used TLS backend, curl may still
load the certificate file specified in CURLOPT_CAINFO(3). curl default settings in some
distributions might use quite a large file as a default setting for CURLOPT_CAINFO(3), so
loading the file can be quite expensive, especially when dealing with many connections.
Thus, in some situations, you might want to disable verification fully to save resources
by setting CURLOPT_CAINFO(3) to NULL - but please also consider the warning above!

DEFAULT

       By default, curl assumes a value of 1.

PROTOCOLS

       All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

EXAMPLE

       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

       If built TLS enabled.

RETURN VALUE

       Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.