=pod

=head1 NAME

provider-serializer - The SERIALIZER library E<lt>-E<gt> provider functions

=head1 SYNOPSIS

=begin comment

Future development will also include deserializing functions.

=end comment

 #include <openssl/core_numbers.h>

 /*
  * None of these are actual functions, but are displayed like this for
  * the function signatures for functions that are offered as function
  * pointers in OSSL_DISPATCH arrays.
  */

 /* Functions to construct / destruct / manipulate the serializer context */
 void *OP_serializer_newctx(void *provctx);
 void OP_serializer_freectx(void *ctx);
 int OP_serializer_set_ctx_params(void *ctx, const OSSL_PARAM params[]);
 const OSSL_PARAM *OP_serializer_settable_ctx_params(void)

 /* Functions to serialize object data */
 int OP_serializer_serialize_data(void *ctx, const OSSL_PARAM *data,
                                  BIO *out,
                                  OSSL_PASSPHRASE_CALLBACK *cb,
                                  void *cbarg);
 int OP_serializer_serialize_object(void *ctx, void *obj, BIO *out,
                                    OSSL_PASSPHRASE_CALLBACK *cb,
                                    void *cbarg);

=head1 DESCRIPTION

The SERIALIZER is a generic method to serialize any set of object data
in L<OSSL_PARAM(3)> array form, or any provider side object into
serialized form, and write it to the given BIO.  If the caller wants
to get the serialized stream to memory, it should provide a
L<BIO_s_membuf(3)>.

The serializer doesn't need to know more about the B<BIO> pointer than
being able to pass it to the appropriate BIO upcalls (see
L<provider-base(7)/Core functions>).

The serialization using the L<OSSL_PARAM(3)> array form allows a
serializer to be used for data that's been exported from another
provider, and thereby allow them to exist independently of each
other.

The serialization using a provider side object can only be safely used
with provider data coming from the same provider, for example keys
with the L<KEYMGMT|provider-keymgmt(7)> provider.

All "functions" mentioned here are passed as function pointers between
F<libcrypto> and the provider in B<OSSL_DISPATCH> arrays via
B<OSSL_ALGORITHM> arrays that are returned by the provider's
provider_query_operation() function
(see L<provider-base(7)/Provider Functions>).

All these "functions" have a corresponding function type definition
named B<OSSL_{name}_fn>, and a helper function to retrieve the
function pointer from a B<OSSL_DISPATCH> element named
B<OSSL_get_{name}>.
For example, the "function" OP_serializer_serialize_data() has these:

 typedef int
     (OSSL_OP_serializer_serialize_data_fn)(void *provctx,
                                            const OSSL_PARAM params[],
                                            BIO *out);
 static ossl_inline OSSL_OP_serializer_serialize_data_fn
     OSSL_get_OP_serializer_serialize_data(const OSSL_DISPATCH *opf);

B<OSSL_DISPATCH> arrays are indexed by numbers that are provided as
macros in L<openssl-core_numbers.h(7)>, as follows:

 OP_serializer_newctx              OSSL_FUNC_SERIALIZER_NEWCTX
 OP_serializer_freectx             OSSL_FUNC_SERIALIZER_FREECTX
 OP_serializer_set_ctx_params      OSSL_FUNC_SERIALIZER_SET_CTX_PARAMS
 OP_serializer_settable_ctx_params OSSL_FUNC_SERIALIZER_SETTABLE_CTX_PARAMS

 OP_serializer_serialize_data      OSSL_FUNC_SERIALIZER_SERIALIZE_DATA
 OP_serializer_serialize_object    OSSL_FUNC_SERIALIZER_SERIALIZE_OBJECT

=head2 Names and properties

The name of an implementation should match the type of object it
handles.  For example, an implementation that serializes an RSA key
should be named accordingly.

To be able to specify exactly what serialization format and what type
of data a serializer implementation is expected to handle, two
additional properties may be given:

=over 4

=item format

This property is used to specify what kind of output format the
implementation produces.  Currently known formats are:

=over 4

=item text

An implementation with that format property value outputs human
readable text, making that implementation suitable for C<-text> output
in diverse L<openssl(1)> commands.

=item pem

An implementation with that format property value outputs PEM
formatted data.

=item der

An implementation with that format property value outputs DER
formatted data.

=back

=item type

With objects that have multiple purposes, this can be used to specify
the purpose type.  The currently known use cases are asymmetric keys
and key parameters, where the type can be one of:

=over 4

=item private

An implementation with that format property value outputs a private
key.

=item public

An implementation with that format property value outputs a public
key.

=item parameters

An implementation with that format property value outputs key
parameters.

=back

=back

The possible values of both these properties is open ended.  A
provider may very well specify other formats that libcrypto doesn't
know anything about.

=head2 Context functions

OP_serializer_newctx() returns a context to be used with the rest of
the functions.

OP_serializer_freectx() frees the given I<ctx>, if it was created by
OP_serializer_newctx().

OP_serializer_set_ctx_params() sets context data according to
parameters from I<params> that it recognises.  Unrecognised parameters
should be ignored.

OP_serializer_settable_ctx_params() returns a constant B<OSSL_PARAM>
array describing the parameters that OP_serializer_set_ctx_params()
can handle.

See L<OSSL_PARAM(3)> for further details on the parameters structure used
by OP_serializer_set_ctx_params() and OP_serializer_settable_ctx_params().

=head2 Serializing functions

=for comment There will be a "Deserializing functions" title as well

OP_serializer_serialize_data() should take an array of B<OSSL_PARAM>,
I<data>, and if it contains the data necessary for the object type
that the implementation handles, it should output the object in
serialized form to the B<BIO>.

OP_serializer_serialize_object() should take a pointer to an object
that it knows intimately, and output that object in serialized form to
the B<BIO>.  The caller I<must> ensure that this function is called
with a pointer that the provider of this function is familiar with.
It is not suitable to use with object pointers coming from other
providers.

Both serialization functions also take an B<OSSL_PASSPHRASE_CALLBACK>
function pointer along with a pointer to application data I<cbarg>,
which should be used when a pass phrase prompt is needed.

=head2 Serializer parameters

Parameters currently recognised by built-in serializers are as
follows:

=over 4

=item "cipher" (B<OSSL_SERIALIZER_PARAM_CIPHER>) <UTF8 string>

The name of the encryption cipher to be used when generating encrypted
serialization.  This is used when serializing private keys, as well as
other objects that need protection.

If this name is invalid for the serialization implementation, the
implementation should refuse to perform the serialization, i.e.
OP_serializer_serialize_data() and OP_serializer_serialize_object()
should return an error.

=item "properties" (B<OSSL_SERIALIZER_PARAM_PROPERTIES>) <UTF8 string>

The properties to be queried when trying to fetch the algorithm given
with the "cipher" parameter.
This must be given together with the "cipher" parameter to be
considered valid.

The serialization implementation isn't obligated to use this value.
However, it is recommended that implementations that do not handle
property strings return an error on receiving this parameter unless
its value NULL or the empty string.

=item "passphrase" (B<OSSL_SERIALIZER_PARAM_PASS>) <octet string>

A pass phrase provided by the application.  When this is given, the
built-in serializers will not attempt to use the passphrase callback.

=back

Parameters currently recognised by the built-in pass phrase callback:

=over 4

=item "info" (B<OSSL_PASSPHRASE_PARAM_INFO>) <UTF8 string>

A string of information that will become part of the pass phrase
prompt.  This could be used to give the user information on what kind
of object it's being prompted for.

=back

=head1 RETURN VALUES

OP_serializer_newctx() returns a pointer to a context, or NULL on
failure.

OP_serializer_set_ctx_params() returns 1, unless a recognised
parameters was invalid or caused an error, for which 0 is returned.

OP_serializer_settable_ctx_params() returns a pointer to an array of
constant B<OSSL_PARAM> elements.

OP_serializer_serialize_data() and OP_serializer_serialize_object()
return 1 on success, or 0 on failure.

=head1 SEE ALSO

L<provider(7)>

=head1 HISTORY

The SERIALIZER interface was introduced 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>.

=cut