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Title "SSL_CTX_SET_CERT_CB 3ossl" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
SSL_CTX_set_cert_cb, SSL_set_cert_cb - handle certificate callback function Header "SYNOPSIS" .Vb 1 #include <openssl/ssl.h> \& void SSL_CTX_set_cert_cb(SSL_CTX *c, int (*cert_cb)(SSL *ssl, void *arg), void *arg); void SSL_set_cert_cb(SSL *s, int (*cert_cb)(SSL *ssl, void *arg), void *arg); .Ve Header "DESCRIPTION" \fBSSL_CTX_set_cert_cb() and SSL_set_cert_cb() sets the cert_cb callback, \fIarg value is pointer which is passed to the application callback.

When cert_cb is \s-1NULL,\s0 no callback function is used.

\fIcert_cb is the application defined callback. It is called before a certificate will be used by a client or server. The callback can then inspect the passed ssl structure and set or clear any appropriate certificates. If the callback is successful it \s-1MUST\s0 return 1 even if no certificates have been set. A zero is returned on error which will abort the handshake with a fatal internal error alert. A negative return value will suspend the handshake and the handshake function will return immediately. \fBSSL_get_error\|(3) will return \s-1SSL_ERROR_WANT_X509_LOOKUP\s0 to indicate, that the handshake was suspended. The next call to the handshake function will again lead to the call of cert_cb. It is the job of the \fIcert_cb to store information about the state of the last call, if required to continue.

Header "NOTES" An application will typically call SSL_use_certificate() and \fBSSL_use_PrivateKey() to set the end entity certificate and private key. It can add intermediate and optionally the root \s-1CA\s0 certificates using \fBSSL_add1_chain_cert().

It might also call SSL_certs_clear() to delete any certificates associated with the \s-1SSL\s0 object.

The certificate callback functionality supersedes the (largely broken) functionality provided by the old client certificate callback interface. It is always called even is a certificate is already set so the callback can modify or delete the existing certificate.

A more advanced callback might examine the handshake parameters and set whatever chain is appropriate. For example a legacy client supporting only TLSv1.0 might receive a certificate chain signed using \s-1SHA1\s0 whereas a TLSv1.2 or later client which advertises support for \s-1SHA256\s0 could receive a chain using \s-1SHA256.\s0

Normal server sanity checks are performed on any certificates set by the callback. So if an \s-1EC\s0 chain is set for a curve the client does not support it will not be used.

Header "RETURN VALUES" \fBSSL_CTX_set_cert_cb() and SSL_set_cert_cb() do not return values. Header "SEE ALSO" \fBssl\|(7), SSL_use_certificate\|(3), \fBSSL_add1_chain_cert\|(3), \fBSSL_get_client_CA_list\|(3), \fBSSL_clear\|(3), SSL_free\|(3) Header "COPYRIGHT" Copyright 2014-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.