X509_STORE_CTX_SET_VERIFY_CB(3SSL)

📦
version 4.0.3 · 14 versions
, in ubuntu stonking

💅 NAME 💅

okay bestie, gather round, because this page is literally a whole squad of functions. We're talking:

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, and X509_STORE_CTX_set_current_reasons

…and what do they do? They get and set X509_STORE_CTX components, like the verification callback. That's the vibe. Periodt. It's an OpenSSL manual page, section 3SSL, just so you know what you walked into. 🦋

✨ 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);

look at all these signatures bestie, it's giving ✨menu✨.

🌸 DESCRIPTION 🌸

X509_STORE_CTX_set_verify_cb() sets the verification callback of ctx to verify_cb, and it overwrites any existing callback. No takebacks, the old one is gone, she's replaced. 💀

So what even is a verification callback? It's your little customizer for certificate verification — you can use it to flex the operation, like overriding error conditions, or logging errors for debugging. Very main character. But lowkey? a verification callback is not essential, and the default operation is often fully sufficient. Don't add one just because she's cute.

The ok parameter handed to the callback tells you the value the callback should return to retain the default behaviour. The lore:

  • If it's zero, an error condition is indicated. 😭
  • If it's 1, no error occurred. 🎀
  • If the flag X509_V_FLAG_NOTIFY_POLICY is set, then ok is set to 2, to indicate the policy checking is complete. ✨

The ctx parameter handed to the callback is the X509_STORE_CTX structure doing the verifying. A callback can snoop on this structure and receive additional info about the error — for example by calling X509_STORE_CTX_get_current_cert(). And you can pass extra application data into the callback via the ex_data mechanism. iykyk.

X509_STORE_CTX_print_verify_cb() is a whole verification callback function on its own. When certificate verification has failed, it adds an entry to the error queue with code X509_R_CERTIFICATE_VERIFICATION_FAILED and with 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. Receipts, basically. 🧾

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

Now the getter gang:

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 them return the function pointers cached from the corresponding X509_STORE. Want more tea on that? Go read X509_STORE_set_verify(3).

X509_STORE_CTX_set_get_crl() sets the function that gets the CRL for a given certificate x. When 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 will be used instead. the more you know 💫

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. no skipping, bestie, it's mandatory.

🚨 WARNINGS 🚨

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. That effectively removes all security from the application, because any certificate — including untrusted, generated ones — will be accepted.

fr fr that's a 💀 moment. do not do that. that's not slay, that's a vulnerability.

📝 NOTES 📝

The verification callback can be set and inherited from the parent structure performing the operation. And in some cases (S/MIME verification being the example given) 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. sneaky, but that's the only door. 🙈

🫶 RETURN VALUES 🫶

X509_STORE_CTX_set_verify_cb() does not return a value. that's it, that's the whole section, she just vibes and returns nothing. 💅

🌈 EXAMPLES 🌈

Default callback operation:

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 the 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)

go read those next bestie, they're the extended universe. 📚

📜 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.

like, we love a glow-up timeline. ⭐

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>.

and that's the whole page, bestie 🎀 mwah 💖 this was OpenSSL 4.0.3, dated 2026-09-29, manual section 3SSL — take care of her, she's iconic 👑

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