=pod

=head1 NAME

OSSL_ENCODER_CTX_new_by_EVP_PKEY,
OSSL_ENCODER_CTX_set_cipher,
OSSL_ENCODER_CTX_set_passphrase,
OSSL_ENCODER_CTX_set_pem_password_cb,
OSSL_ENCODER_CTX_set_passphrase_cb,
OSSL_ENCODER_CTX_set_passphrase_ui
- Encoder routines to encode EVP_PKEYs

=head1 SYNOPSIS

 #include <openssl/encoder.h>

 OSSL_ENCODER_CTX *
 OSSL_ENCODER_CTX_new_by_EVP_PKEY(const EVP_PKEY *pkey,
                                  const char *output_type, int selection,
                                  OSSL_LIB_CTX *libctx, const char *propquery);

 int OSSL_ENCODER_CTX_set_cipher(OSSL_ENCODER_CTX *ctx,
                                 const char *cipher_name,
                                 const char *propquery);
 int OSSL_ENCODER_CTX_set_passphrase(OSSL_ENCODER_CTX *ctx,
                                     const unsigned char *kstr,
                                     size_t klen);
 int OSSL_ENCODER_CTX_set_pem_password_cb(OSSL_ENCODER_CTX *ctx,
                                          pem_password_cb *cb, void *cbarg);
 int OSSL_ENCODER_CTX_set_passphrase_ui(OSSL_ENCODER_CTX *ctx,
                                        const UI_METHOD *ui_method,
                                        void *ui_data);
 int OSSL_ENCODER_CTX_set_passphrase_cb(OSSL_ENCODER_CTX *ctx,
                                        OSSL_PASSPHRASE_CALLBACK *cb,
                                        void *cbarg);

=head1 DESCRIPTION

OSSL_ENCODER_CTX_new_by_EVP_PKEY() is a utility function that creates a
B<OSSL_ENCODER_CTX>, finds all applicable encoder implementations and sets
them up, so almost all the caller has to do next is call functions like
L<OSSL_ENCODER_to_bio(3)>.

Internally, OSSL_ENCODER_CTX_new_by_EVP_PKEY() uses the names from the
L<EVP_KEYMGMT(3)> implementation associated with I<pkey> to build a list of
applicable encoder implementations that are used to process the I<pkey> into
the encoding named by I<output_type>.  All these implementations are
implicitly fetched using I<libctx> and I<propquery>.

If no suitable encoder implementation is found,
OSSL_ENCODER_CTX_new_by_EVP_PKEY() still creates a B<OSSL_ENCODER_CTX>, but
with no associated encoder (L<OSSL_ENCODER_CTX_get_num_encoders(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_ENCODER_CTX_set_cipher() tells the implementation what cipher
should be used to encrypt encoded keys.  The cipher is given by
name I<cipher_name>.  The interpretation of that I<cipher_name> is
implementation dependent.  The implementation may implement the cipher
directly itself or by other implementations, or it may choose to fetch
it.  If the implementation supports fetching the cipher, then it may
use I<propquery> as properties to be queried for when fetching.
I<cipher_name> may also be NULL, which will result in unencrypted
encoding.

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

OSSL_ENCODER_CTX_set_pem_password_cb(), OSSL_ENCODER_CTX_set_passphrase_ui()
and OSSL_ENCODER_CTX_set_passphrase_cb() sets 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.

=head1 RETURN VALUES

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

OSSL_ENCODER_CTX_set_cipher(), OSSL_ENCODER_CTX_set_passphrase(),
OSSL_ENCODER_CTX_set_pem_password_cb(), OSSL_ENCODER_CTX_set_passphrase_ui()
and OSSL_ENCODER_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_ENCODER_CTX_new_by_EVP_PKEY() matches the type name,
thus making for the naming pattern B<OSSL_ENCODER_CTX_new_by_I<TYPE>>() when
new types are handled.

=head1 SEE ALSO

L<provider(7)>, L<OSSL_ENCODER(3)>, L<OSSL_ENCODER_CTX(3)>

=head1 HISTORY

The functions described here were added in OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2019-2020 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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