=pod

=head1 NAME

OSSL_DECODER_CTX_new_by_EVP_PKEY,
OSSL_DECODER_CTX_set_passphrase,
OSSL_DECODER_CTX_set_pem_password_cb,
OSSL_DECODER_CTX_set_passphrase_ui,
OSSL_DECODER_CTX_set_passphrase_cb
- Decoder routines to decode EVP_PKEYs

=head1 SYNOPSIS

 #include <openssl/decoder.h>

 OSSL_DECODER_CTX *
 OSSL_DECODER_CTX_new_by_EVP_PKEY(const EVP_PKEY *pkey,
                                  const char *input_type, const char *keytype,
                                  OSSL_LIB_CTX *libctx, const char *propquery);

 int OSSL_DECODER_CTX_set_passphrase(OSSL_DECODER_CTX *ctx,
                                     const unsigned char *kstr,
                                     size_t klen);
 int OSSL_DECODER_CTX_set_pem_password_cb(OSSL_DECODER_CTX *ctx,
                                          pem_password_cb *cb,
                                          void *cbarg);
 int OSSL_DECODER_CTX_set_passphrase_ui(OSSL_DECODER_CTX *ctx,
                                        const UI_METHOD *ui_method,
                                        void *ui_data);
 int OSSL_DECODER_CTX_set_passphrase_cb(OSSL_DECODER_CTX *ctx,
                                        OSSL_PASSPHRASE_CALLBACK *cb,
                                        void *cbarg);

=head1 DESCRIPTION

OSSL_DECODER_CTX_new_by_EVP_PKEY() is a utility function that creates a
B<OSSL_DECODER_CTX>, finds all applicable decoder implementations and sets
them up, so all the caller has to do next is call functions like
OSSL_DECODE_from_bio().

Internally OSSL_DECODER_CTX_new_by_EVP_PKEY() searches for all available
L<EVP_KEYMGMT(3)> implementations, and then builds a list of all potential
decoder implementations that may be able to process the encoded input into
data suitable for B<EVP_PKEY>s.  All these implementations are implicitly
fetched using I<libctx> and I<propquery>.

The search of decoder implementations can be limited with I<input_type>,
which specifies a starting input type.  NULL is valid input and signifies
that the decoder implementations will find out the input type on their own.
This is further explained in L<OSSL_DECODER_CTX_set_input_type(3)>.

The search of decoder implementations can also be limited with I<keytype>,
which specifies the expected resulting keytype.  NULL is valid input and
signifies that the decoder implementations will find out the keytype on
their own from the input they get.

If no suitable decoder implementation is found,
OSSL_DECODER_CTX_new_by_EVP_PKEY() still creates a B<OSSL_DECODER_CTX>, but
with no associated decoder (L<OSSL_DECODER_CTX_get_num_decoders(3)> returns
zero).  This helps the caller to distinguish between an error when creating
the B<OSSL_ENCODER_CTX> and missing encoder implementation, and allows it to
act accordingly.

OSSL_DECODER_CTX_set_passphrase() gives the implementation a pass phrase to
use when decrypting the encoded private key. Alternatively, a pass phrase
callback may be specified with the following functions.

OSSL_DECODER_CTX_set_pem_password_cb(), OSSL_DECODER_CTX_set_passphrase_ui()
and OSSL_DECODER_CTX_set_passphrase_cb() set up a callback method that the
implementation can use to prompt for a pass phrase, giving the caller the
choice of prefered pass phrase callback form.  These are called indirectly,
through an internal B<OSSL_PASSPHRASE_CALLBACK> function.

The internal B<OSSL_PASSPHRASE_CALLBACK> function caches the pass phrase, to
be re-used in all decodings that are performed in the same decoding run (for
example, within one L<OSSL_DECODER_from_bio(3)> call).

=head1 RETURN VALUES

OSSL_DECODER_CTX_new_by_EVP_PKEY() returns a pointer to a
B<OSSL_DECODER_CTX>, or NULL if it couldn't be created.

OSSL_DECODER_CTX_set_passphrase(), OSSL_DECODER_CTX_set_pem_password_cb(),
OSSL_DECODER_CTX_set_passphrase_ui() and
OSSL_DECODER_CTX_set_passphrase_cb() all return 1 on success, or 0 on
failure.

=head1 NOTES

Parts of the function names are made to match already existing OpenSSL
names.

B<EVP_PKEY> in OSSL_DECODER_CTX_new_by_EVP_PKEY() matches the type name,
thus making for the naming pattern B<OSSL_DECODER_CTX_new_by_I<TYPE>>() when
new types are handled.

=head1 SEE ALSO

L<provider(7)>, L<OSSL_DECODER(3)>, L<OSSL_DECODER_CTX(3)>

=head1 HISTORY

The functions described here were added in OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2020 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
L<https://www.openssl.org/source/license.html>.

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