X509_STORE_CTX_SET_VERIFY_CB(3ossl)

📦 version 3.5.0, in opensuse-leap 16.0

💅 NAME

okay so bestie, this whole page is a big ol' family of X509_STORE_CTX getter/setter girlies — like, this is the OpenSSL 3ossl manual page for:

X509_STORE_CTX_get_cleanup, X509_STORE_CTX_get_lookup_crls, X509_STORE_CTX_get_lookup_certs, X509_STORE_CTX_get_check_policy, X509_STORE_CTX_get_cert_crl, X509_STORE_CTX_get_check_crl, X509_STORE_CTX_get_get_crl, X509_STORE_CTX_set_get_crl, X509_STORE_CTX_get_check_revocation, X509_STORE_CTX_get_check_issued, X509_STORE_CTX_get_get_issuer, X509_STORE_CTX_get_verify_cb, X509_STORE_CTX_set_verify_cb, X509_STORE_CTX_verify_cb, X509_STORE_CTX_print_verify_cb, X509_STORE_CTX_set_current_reasons

and collectively they get and set X509_STORE_CTX components — like the verification callback, which is literally the main character here. 👑

✨ SYNOPSIS ✨

#include <openssl/x509_vfy.h>

typedef int (*X509_STORE_CTX_verify_cb)(int, X509_STORE_CTX *);
int X509_STORE_CTX_print_verify_cb(int ok, X509_STORE_CTX *ctx);

X509_STORE_CTX_verify_cb X509_STORE_CTX_get_verify_cb(X509_STORE_CTX *ctx);

void X509_STORE_CTX_set_verify_cb(X509_STORE_CTX *ctx,
                                  X509_STORE_CTX_verify_cb verify_cb);

X509_STORE_CTX_get_issuer_fn X509_STORE_CTX_get_get_issuer(X509_STORE_CTX *ctx);
X509_STORE_CTX_check_issued_fn X509_STORE_CTX_get_check_issued(X509_STORE_CTX *ctx);
X509_STORE_CTX_check_revocation_fn X509_STORE_CTX_get_check_revocation(X509_STORE_CTX *ctx);

X509_STORE_CTX_get_crl_fn X509_STORE_CTX_get_get_crl(X509_STORE_CTX *ctx);

void X509_STORE_CTX_set_get_crl(X509_STORE_CTX *ctx,
                                X509_STORE_CTX_get_crl_fn get_crl);

X509_STORE_CTX_check_crl_fn X509_STORE_CTX_get_check_crl(X509_STORE_CTX *ctx);
X509_STORE_CTX_cert_crl_fn X509_STORE_CTX_get_cert_crl(X509_STORE_CTX *ctx);
X509_STORE_CTX_check_policy_fn X509_STORE_CTX_get_check_policy(X509_STORE_CTX *ctx);
X509_STORE_CTX_lookup_certs_fn X509_STORE_CTX_get_lookup_certs(X509_STORE_CTX *ctx);
X509_STORE_CTX_lookup_crls_fn X509_STORE_CTX_get_lookup_crls(X509_STORE_CTX *ctx);
X509_STORE_CTX_cleanup_fn X509_STORE_CTX_get_cleanup(X509_STORE_CTX *ctx);
void X509_STORE_CTX_set_current_reasons(X509_STORE_CTX *ctx,
                                        unsigned int current_reasons);

🦋 DESCRIPTION

X509_STORE_CTX_set_verify_cb() sets the verification callback of ctx to verify_cb, and like… it overwrites any callback that was already chilling there. No loyalty, it just replaces her. 💀

So what's the callback even for? It lets you customise how certificate verification behaves — for instance by overriding error conditions, or by logging errors for debugging. It's giving "let me peek behind the curtain."

But bestie, hear me: a verification callback is not essential. The default operation is often perfectly sufficient. Don't add one just because you can. 🙈

Now the ok parameter that gets passed to your callback? That's the value the callback should return to retain the default behaviour. Let's break it down:

  • If it's 0 then an error condition is indicated.
  • If it's 1 then no error occurred.
  • If the flag X509_V_FLAG_NOTIFY_POLICY is set then ok is set to 2, which means the policy checking is complete. 🎉

The ctx parameter is the X509_STORE_CTX structure doing the actual verifying. Your callback can poke around in it and get extra info about the error — like by calling X509_STORE_CTX_get_current_cert(), for example. And you can pass additional application data into the callback via the ex_data mechanism. Very handy, very slay. 🫶

X509_STORE_CTX_print_verify_cb() is itself a verification callback function, and what it does is: when certificate verification has failed, it adds an entry to the error queue with code X509_R_CERTIFICATE_VERIFICATION_FAILED plus diagnostic details — including the most relevant fields of the target certificate that failed to verify, and, if appropriate, of the available untrusted and trusted certificates. So like, a full receipt of the drama. 🧾

X509_STORE_CTX_get_verify_cb() returns the value of the current callback for that specific ctx. Simple.

Then we got a whole squad of getters — X509_STORE_CTX_get_get_issuer(), X509_STORE_CTX_get_check_issued(), X509_STORE_CTX_get_check_revocation(), X509_STORE_CTX_get_get_crl(), X509_STORE_CTX_get_check_crl(), X509_STORE_CTX_get_cert_crl(), X509_STORE_CTX_get_check_policy(), X509_STORE_CTX_get_lookup_certs(), X509_STORE_CTX_get_lookup_crls() and X509_STORE_CTX_get_cleanup(). All of these return the function pointers cached from the corresponding X509_STORE. For more info, go see X509_STORE_set_verify(3). ✨

X509_STORE_CTX_set_get_crl() sets the function to get the CRL for a given certificate x. When it's found, the CRL must be assigned to *crl. This function must return 0 on failure and 1 on success. And if no function to get the issuer is provided, the internal default function is used instead. 👑

X509_STORE_CTX_set_current_reasons() is used in conjunction with X509_STORE_CTX_get_crl_fn. The X509_STORE_CTX_get_crl_fn callback must use this method to set the reason why the certificate is invalid. Like, that's the assignment, bestie.

🚨 WARNINGS 🚨

Okay this is the serious one, so lock in:

In general a verification callback should NOT unconditionally return 1 in all circumstances, because this will allow verification to succeed no matter what the error is. This effectively removes all security from the application, because any certificate — including untrusted generated ones — will be accepted. 💀💀💀

Like genuinely, do not do that. That's not a glow-up, that's a security hole.

🌸 NOTES

The verification callback can be set and inherited from the parent structure performing the operation. In some cases (like S/MIME verification), the X509_STORE_CTX structure is created and destroyed internally — so the only way to set a custom verification callback is by inheriting it from the associated X509_STORE. iykyk. 🌈

⭐ RETURN VALUES

X509_STORE_CTX_set_verify_cb() does not return a value. Nothing. Nada. It's above that. 💅

🔥 EXAMPLES 🔥

Default callback operation — the low-effort iconique version:

int verify_callback(int ok, X509_STORE_CTX *ctx) {
    return ok;
}

Simple example — suppose a certificate in the chain is expired and we wish to continue after this error:

int verify_callback(int ok, X509_STORE_CTX *ctx) {
    /* Tolerate certificate expiration */
    if (X509_STORE_CTX_get_error(ctx) == X509_V_ERR_CERT_HAS_EXPIRED)
        return 1;
    /* Otherwise don't override */
    return ok;
}

More complex example — we don't wish to continue after any certificate has expired, just one specific case:

int verify_callback(int ok, X509_STORE_CTX *ctx)
{
    int err = X509_STORE_CTX_get_error(ctx);
    X509 *err_cert = X509_STORE_CTX_get_current_cert(ctx);

    if (err == X509_V_ERR_CERT_HAS_EXPIRED) {
        if (check_is_acceptable_expired_cert(err_cert)
            return 1;
    }
    return ok;
}

Full featured logging callback. In this case bio_err is assumed to be a global logging BIO — an alternative would be to store a BIO in ctx using ex_data:

int verify_callback(int ok, X509_STORE_CTX *ctx)
{
    X509 *err_cert;
    int err, depth;

    err_cert = X509_STORE_CTX_get_current_cert(ctx);
    err = X509_STORE_CTX_get_error(ctx);
    depth = X509_STORE_CTX_get_error_depth(ctx);

    BIO_printf(bio_err, "depth=%d ", depth);
    if (err_cert) {
        X509_NAME_print_ex(bio_err, X509_get_subject_name(err_cert),
                           0, XN_FLAG_ONELINE);
        BIO_puts(bio_err, "\n");
    }
    else
        BIO_puts(bio_err, "<no cert>\n");
    if (!ok)
        BIO_printf(bio_err, "verify error:num=%d:%s\n", err,
                   X509_verify_cert_error_string(err));
    switch (err) {
    case X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT:
        BIO_puts(bio_err, "issuer= ");
        X509_NAME_print_ex(bio_err, X509_get_issuer_name(err_cert),
                           0, XN_FLAG_ONELINE);
        BIO_puts(bio_err, "\n");
        break;
    case X509_V_ERR_CERT_NOT_YET_VALID:
    case X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD:
        BIO_printf(bio_err, "notBefore=");
        ASN1_TIME_print(bio_err, X509_get_notBefore(err_cert));
        BIO_printf(bio_err, "\n");
        break;
    case X509_V_ERR_CERT_HAS_EXPIRED:
    case X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD:
        BIO_printf(bio_err, "notAfter=");
        ASN1_TIME_print(bio_err, X509_get_notAfter(err_cert));
        BIO_printf(bio_err, "\n");
        break;
    case X509_V_ERR_NO_EXPLICIT_POLICY:
        policies_print(bio_err, ctx);
        break;
    }
    if (err == X509_V_OK && ok == 2)
        /* print out policies */

    BIO_printf(bio_err, "verify return:%d\n", ok);
    return(ok);
}

👀 SEE ALSO

X509_STORE_CTX_get_error(3) X509_STORE_set_verify_cb_func(3) X509_STORE_CTX_get_ex_new_index(3)

🎀 HISTORY

The X509_STORE_CTX_get_get_issuer(), X509_STORE_CTX_get_check_issued(), X509_STORE_CTX_get_check_revocation(), X509_STORE_CTX_get_get_crl(), X509_STORE_CTX_get_check_crl(), X509_STORE_CTX_get_cert_crl(), X509_STORE_CTX_get_check_policy(), X509_STORE_CTX_get_lookup_certs(), X509_STORE_CTX_get_lookup_crls() and X509_STORE_CTX_get_cleanup() functions were added in OpenSSL 1.1.0. 🕰️

X509_STORE_CTX_print_verify_cb() was added in OpenSSL 3.0.

Copyright 2009-2023 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

okay that's the whole thing bestie, mwah 💋 — this lil' page comes to you straight from OpenSSL 3.5.0, dated 2026-09-2 on the footer, and yes she ate. 🍓🧚💜

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