PROVIDER-ENCODER(7SSL) OpenSSL PROVIDER-ENCODER(7SSL)
NAME
provider-encoder - The OSSL_ENCODER library <-> provider functions
SYNOPSIS
#include <openssl/core_dispatch.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.
*/
/* Encoder parameter accessor and descriptor */
const OSSL_PARAM *OSSL_FUNC_encoder_gettable_params(void *provctx);
int OSSL_FUNC_encoder_get_params(OSSL_PARAM params[]);
/* Functions to construct / destruct / manipulate the encoder context */
void *OSSL_FUNC_encoder_newctx(void *provctx);
void OSSL_FUNC_encoder_freectx(void *ctx);
int OSSL_FUNC_encoder_set_ctx_params(void *ctx, const OSSL_PARAM params[]);
const OSSL_PARAM *OSSL_FUNC_encoder_settable_ctx_params(void *provctx);
/* Functions to check selection support */
int OSSL_FUNC_encoder_does_selection(void *provctx, int selection);
/* Functions to encode object data */
int OSSL_FUNC_encoder_encode(void *ctx, OSSL_CORE_BIO *out,
const void *obj_raw,
const OSSL_PARAM obj_abstract[],
int selection,
OSSL_PASSPHRASE_CALLBACK *cb,
void *cbarg);
/* Functions to import and free a temporary object to be encoded */
void *OSSL_FUNC_encoder_import_object(void *ctx, int selection,
const OSSL_PARAM params[]);
void OSSL_FUNC_encoder_free_object(void *obj);
DESCRIPTION
We use the wide term "encode" in this manual. This includes but is not
limited to serialization.
The ENCODER operation is a generic method to encode a provider-native
object (obj_raw) or an object abstraction (object_abstract, see
provider-object(7)) into an encoded form, and write the result to the
given OSSL_CORE_BIO. If the caller wants to get the encoded stream to
memory, it should provide a BIO_s_mem(3) BIO.
The encoder doesn't need to know more about the OSSL_CORE_BIO pointer
than being able to pass it to the appropriate BIO upcalls (see "Core
functions" in provider-base(7)).
The ENCODER implementation may be part of a chain, where data is passed
from one to the next. For example, there may be an implementation to
encode an object to DER (that object is assumed to be provider-native
and thereby passed via obj_raw), and another one that encodes DER to PEM
(that one would receive the DER encoding via obj_abstract).
The encoding using the OSSL_PARAM(3) array form allows a encoder to be
used for data that's been exported from another provider, and thereby
allow them to exist independently of each other.
The encoding using a provider side object can only be safely used with
provider data coming from the same provider, for example keys with the
KEYMGMT provider.
All "functions" mentioned here are passed as function pointers between
libcrypto and the provider in OSSL_DISPATCH(3) arrays via
OSSL_ALGORITHM(3) arrays that are returned by the provider's
provider_query_operation() function (see "Provider Functions" in
provider-base(7)).
All these "functions" have a corresponding function type definition
named OSSL_FUNC_{name}_fn, and a helper function to retrieve the
function pointer from an OSSL_DISPATCH(3) element named
OSSL_FUNC_{name}. For example, the "function"
OSSL_FUNC_encoder_encode() has these:
typedef int
(OSSL_FUNC_encoder_encode_fn)(void *ctx, OSSL_CORE_BIO *out,
const void *obj_raw,
const OSSL_PARAM obj_abstract[],
int selection,
OSSL_PASSPHRASE_CALLBACK *cb, void *cbarg);
static ossl_inline OSSL_FUNC_encoder_encode_fn
OSSL_FUNC_encoder_encode(const OSSL_DISPATCH *opf);
OSSL_DISPATCH(3) arrays are indexed by numbers that are provided as
macros in openssl-core_dispatch.h(7), as follows:
OSSL_FUNC_encoder_get_params OSSL_FUNC_ENCODER_GET_PARAMS
OSSL_FUNC_encoder_gettable_params OSSL_FUNC_ENCODER_GETTABLE_PARAMS
OSSL_FUNC_encoder_newctx OSSL_FUNC_ENCODER_NEWCTX
OSSL_FUNC_encoder_freectx OSSL_FUNC_ENCODER_FREECTX
OSSL_FUNC_encoder_set_ctx_params OSSL_FUNC_ENCODER_SET_CTX_PARAMS
OSSL_FUNC_encoder_settable_ctx_params OSSL_FUNC_ENCODER_SETTABLE_CTX_PARAMS
OSSL_FUNC_encoder_does_selection OSSL_FUNC_ENCODER_DOES_SELECTION
OSSL_FUNC_encoder_encode OSSL_FUNC_ENCODER_ENCODE
OSSL_FUNC_encoder_import_object OSSL_FUNC_ENCODER_IMPORT_OBJECT
OSSL_FUNC_encoder_free_object OSSL_FUNC_ENCODER_FREE_OBJECT
Names and properties
The name of an implementation should match the type of object it
handles. For example, an implementation that encodes an RSA key should
be named "RSA". Likewise, an implementation that further encodes DER
should be named "DER".
Properties, as defined in the OSSL_ALGORITHM(3) array element of each
decoder implementation, can be used to further specify details about an
implementation:
output
This property is used to specify what type of output the
implementation produces.
This property is mandatory.
OpenSSL providers recognize the following output types:
text
An implementation with that output type outputs human readable
text, making that implementation suitable for "-text" output in
diverse openssl(1) commands.
pem An implementation with that output type outputs PEM formatted
data.
der An implementation with that output type outputs DER formatted
data.
msblob
An implementation with that output type outputs MSBLOB formatted
data.
pvk An implementation with that output type outputs PVK formatted
data.
structure
This property is used to specify the structure that is used for the
encoded object. An example could be "pkcs8", to specify explicitly
that an object (presumably an asymmetric key pair, in this case)
will be wrapped in a PKCS#8 structure as part of the encoding.
This property is optional.
The possible values of both these properties is open ended. A provider
may very well specify output types and structures that libcrypto doesn't
know anything about.
Subset selections
Sometimes, an object has more than one subset of data that is
interesting to treat separately or together. It's possible to specify
what subsets are to be encoded, with a set of bits selection that are
passed in an int.
This set of bits depend entirely on what kind of provider-side object is
passed. For example, those bits are assumed to be the same as those
used with provider-keymgmt(7) (see "Key Objects" in provider-keymgmt(7))
when the object is an asymmetric keypair.
ENCODER implementations are free to regard the selection as a set of
hints, but must do so with care. In the end, the output must make
sense, and if there's a corresponding decoder, the resulting decoded
object must match the original object that was encoded.
OSSL_FUNC_encoder_does_selection() should tell if a particular
implementation supports any of the combinations given by selection.
Context functions
OSSL_FUNC_encoder_newctx() returns a context to be used with the rest of
the functions.
OSSL_FUNC_encoder_freectx() frees the given ctx, if it was created by
OSSL_FUNC_encoder_newctx().
OSSL_FUNC_encoder_set_ctx_params() sets context data according to
parameters from params that it recognises. Unrecognised parameters
should be ignored. Passing NULL for params should return true.
OSSL_FUNC_encoder_settable_ctx_params() returns a constant OSSL_PARAM(3)
array describing the parameters that OSSL_FUNC_encoder_set_ctx_params()
can handle.
See OSSL_PARAM(3) for further details on the parameters structure used
by OSSL_FUNC_encoder_set_ctx_params() and
OSSL_FUNC_encoder_settable_ctx_params().
Import functions
A provider-native object may be associated with a foreign provider, and
may therefore be unsuitable for direct use with a given ENCODER
implementation. Provided that the foreign provider's implementation to
handle the object has a function to export that object in OSSL_PARAM(3)
array form, the ENCODER implementation should be able to import that
array and create a suitable object to be passed to
OSSL_FUNC_encoder_encode()'s obj_raw.
OSSL_FUNC_encoder_import_object() should import the subset of params
given with selection to create a provider-native object that can be
passed as obj_raw to OSSL_FUNC_encoder_encode().
OSSL_FUNC_encoder_free_object() should free the object that was created
with OSSL_FUNC_encoder_import_object().
Encoding functions
OSSL_FUNC_encoder_encode() should take a provider-native object (in
obj_raw) or an object abstraction (in obj_abstract), and should output
the object in encoded form to the OSSL_CORE_BIO. The selection bits, if
relevant, should determine in greater detail what will be output. The
encoding functions also take an OSSL_PASSPHRASE_CALLBACK(3) function
pointer along with a pointer to application data cbarg, which should be
used when a pass phrase prompt is needed.
Encoder operation parameters
Operation parameters currently recognised by built-in encoders are as
follows:
"cipher" (OSSL_ENCODER_PARAM_CIPHER) <UTF8 string>
The name of the encryption cipher to be used when generating
encrypted encoding. This is used when encoding private keys, as
well as other objects that need protection.
If this name is invalid for the encoding implementation, the
implementation should refuse to perform the encoding, i.e.
OSSL_FUNC_encoder_encode_data() and
OSSL_FUNC_encoder_encode_object() should return an error.
"properties" (OSSL_ENCODER_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 encoding 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.
"save-parameters" (OSSL_ENCODER_PARAM_SAVE_PARAMETERS) <integer>
If set to 0 disables saving of key domain parameters. Default is 1.
It currently has an effect only on DSA keys.
Parameters currently recognised by the built-in pass phrase callback:
"info" (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.
RETURN VALUES
OSSL_FUNC_encoder_newctx() returns a pointer to a context, or NULL on
failure.
OSSL_FUNC_encoder_set_ctx_params() returns 1, unless a recognised
parameter was invalid or caused an error, for which 0 is returned.
OSSL_FUNC_encoder_settable_ctx_params() returns a pointer to an array of
constant OSSL_PARAM(3) elements.
OSSL_FUNC_encoder_does_selection() returns 1 if the encoder
implementation supports any of the selection bits, otherwise 0.
OSSL_FUNC_encoder_encode() returns 1 on success, or 0 on failure.
SEE ALSO
provider(7)
HISTORY
The ENCODER interface was introduced in OpenSSL 3.0.
COPYRIGHT
Copyright 2019-2025 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>.
3.5.4 2025-09-30 PROVIDER-ENCODER(7SSL)
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