---
name: "libressl-SSL_CTX_set_cert_verify_callback"
section: "3"
platform: "linux"
package: "libressl"
version: "4.4.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/libressl-SSL_CTX_set_cert_verify_callback"
---

# libressl-SSL\_CTX\_set\_cert\_verify\_callback(3)

set peer certificate verification procedure

## NAME

**SSL\_CTX\_set\_cert\_verify\_callback** – set peer certificate verification procedure

## SYNOPSIS

SSL Library (libssl, -lssl) libcrypto

**#include \<openssl/ssl.h\>**

*void*\

**SSL\_CTX\_set\_cert\_verify\_callback**(*SSL\_CTX \*ctx*, *int (\*callback)(X509\_STORE\_CTX \*, void \*)*, *void \*arg*);

## DESCRIPTION

**SSL\_CTX\_set\_cert\_verify\_callback**() sets the verification callback function for *ctx*. *SSL* objects that are created from *ctx* inherit the setting valid at the time when SSL\_new(3) is called.

Whenever a certificate is verified during an SSL/TLS handshake, a verification function is called. If the application does not explicitly specify a verification callback function, the built-in verification function is used. If a verification callback *callback* is specified via **SSL\_CTX\_set\_cert\_verify\_callback**(), the supplied callback function is called instead. By setting *callback* to NULL, the default behaviour is restored.

When the verification must be performed, *callback* will be called with the arguments **callback**(*X509\_STORE\_CTX \*x509\_store\_ctx*, *void \*arg*). The argument *arg* is specified by the application when setting *callback*.

*callback* should return 1 to indicate verification success and 0 to indicate verification failure. If SSL\_VERIFY\_PEER is set and *callback* returns 0, the handshake will fail. As the verification procedure may allow the connection to continue in case of failure (by always returning 1) the verification result must be set in any case using the *error* member of *x509\_store\_ctx* so that the calling application will be informed about the detailed result of the verification procedure!

Within *x509\_store\_ctx*, *callback* has access to the *verify\_callback* function set using SSL\_CTX\_set\_verify(3).

## SEE ALSO

[ssl(3)](/ssl/3.md), SSL\_CTX\_load\_verify\_locations(3), SSL\_CTX\_set\_verify(3), SSL\_get\_verify\_result(3)

## HISTORY

**SSL\_CTX\_set\_cert\_verify\_callback**() first appeared in SSLeay 0.6.1 and has been available since OpenBSD 2.4.

Previous to OpenSSL 0.9.7, the *arg* argument to **SSL\_CTX\_set\_cert\_verify\_callback**() was ignored, and *callback* was called simply as *int* **(\*callback)**(*X509\_STORE\_CTX \**). To compile software written for previous versions of OpenSSL, a dummy argument will have to be added to *callback*.

## CAVEATS

Do not mix the verification callback described in this function with the *verify\_callback* function called during the verification process. The latter is set using the SSL\_CTX\_set\_verify(3) family of functions.

Providing a complete verification procedure including certificate purpose settings, etc., is a complex task. The built-in procedure is quite powerful and in most cases it should be sufficient to modify its behaviour using the *verify\_callback* function.

## BUGS

**SSL\_CTX\_set\_cert\_verify\_callback**() does not provide diagnostic information.