Updated: 2022/Sep/29

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OSSL_CALLBACK(3)                    OpenSSL                   OSSL_CALLBACK(3)



NAME
       OSSL_CALLBACK, OSSL_PASSPHRASE_CALLBACK - OpenSSL Core type to define
       callbacks

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/core.h>
        typedef int (OSSL_CALLBACK)(const OSSL_PARAM params[], void *arg);
        typedef int (OSSL_PASSPHRASE_CALLBACK)(char *pass, size_t pass_size,
                                               size_t *pass_len,
                                               const OSSL_PARAM params[],
                                               void *arg);

DESCRIPTION
       For certain events or activities, provider functionality may need help
       from the application or the calling OpenSSL libraries themselves.  For
       example, user input or direct (possibly optional) user output could be
       implemented this way.

       Callback functions themselves are always provided by or through the
       calling OpenSSL libraries, along with a generic pointer to data arg.
       As far as the function receiving the pointer to the function pointer
       and arg is concerned, the data that arg points at is opaque, and the
       pointer should simply be passed back to the callback function when it's
       called.

       OSSL_CALLBACK
           This is a generic callback function.  When calling this callback
           function, the caller is expected to build an OSSL_PARAM(3) array of
           data it wants or is expected to pass back, and pass that as params,
           as well as the opaque data pointer it received, as arg.

       OSSL_PASSPHRASE_CALLBACK
           This is a specialised callback function, used specifically to
           prompt the user for a passphrase.  When calling this callback
           function, a buffer to store the pass phrase needs to be given with
           pass, and its size with pass_size.  The length of the prompted pass
           phrase will be given back in *pass_len.

           Additional parameters can be passed with the OSSL_PARAM(3) array
           params,

SEE ALSO
       openssl-core.h(7)

HISTORY
       The types described here were added in OpenSSL 3.0.

COPYRIGHT
       Copyright 2022 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>.



3.0.12                            2023-05-07                  OSSL_CALLBACK(3)