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SSL_CTX_set_cert_cb(3) OpenSSL SSL_CTX_set_cert_cb(3)
SSL_CTX_set_cert_cb, SSL_set_cert_cb - handle certificate callback
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);
int (*cert_cb)(SSL *ssl, void *arg);
SSL_CTX_set_cert_cb() and SSL_set_cert_cb() sets the cceerrtt__ccbb(())
callback, arg value is pointer which is passed to the application
When cceerrtt__ccbb(()) is NULL, no callback function is used.
cert_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 MUST 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. SSL_get_error(3) will return
SSL_ERROR_WANT_X509_LOOKUP 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 cert_cb() to store
information about the state of the last call, if required to continue.
An application will typically call SSL_use_certificate() and
SSL_use_PrivateKey() to set the end entity certificate and private key.
It can add intermediate and optionally the root CA certificates using
It might also call SSL_certs_clear() to delete any certificates
associated with the SSL object.
The certificate callback functionality supercedes 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 TLS v1.0 might receive a certificate chain signed using SHA1
whereas a TLS v1.2 client which advertises support for SHA256 could
receive a chain using SHA256.
Normal server sanity checks are performed on any certificates set by
the callback. So if an EC chain is set for a curve the client does not
support it will not be used.
ssl(3), SSL_use_certificate(3), SSL_add1_chain_cert(3),
SSL_get_client_CA_list(3), SSL_clear(3), SSL_free(3)
1.0.2h 2016-05-03 SSL_CTX_set_cert_cb(3)