PROVIDER-DECODER(7SSL) OpenSSL PROVIDER-DECODER(7SSL)
NAME
provider-decoder - The OSSL_DECODER 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.
*/
/* Decoder parameter accessor and descriptor */
const OSSL_PARAM *OSSL_FUNC_decoder_gettable_params(void *provctx);
int OSSL_FUNC_decoder_get_params(OSSL_PARAM params[]);
/* Functions to construct / destruct / manipulate the decoder context */
void *OSSL_FUNC_decoder_newctx(void *provctx);
void OSSL_FUNC_decoder_freectx(void *ctx);
const OSSL_PARAM *OSSL_FUNC_decoder_settable_ctx_params(void *provctx);
int OSSL_FUNC_decoder_set_ctx_params(void *ctx, const OSSL_PARAM params[]);
/* Functions to check selection support */
int OSSL_FUNC_decoder_does_selection(void *provctx, int selection);
/* Functions to decode object data */
int OSSL_FUNC_decoder_decode(void *ctx, OSSL_CORE_BIO *in,
int selection,
OSSL_CALLBACK *data_cb, void *data_cbarg,
OSSL_PASSPHRASE_CALLBACK *cb, void *cbarg);
/* Functions to export a decoded object */
int OSSL_FUNC_decoder_export_object(void *ctx,
const void *objref, size_t objref_sz,
OSSL_CALLBACK *export_cb,
void *export_cbarg);
DESCRIPTION
The term "decode" is used throughout this manual. This includes but is
not limited to deserialization as individual decoders can also do
decoding into intermediate data formats.
The DECODER operation is a generic method to create a provider-native
object reference or intermediate decoded data from an encoded form read
from the given OSSL_CORE_BIO. If the caller wants to decode data from
memory, it should provide a BIO_s_mem(3) BIO. The decoded data or object
reference is passed along with eventual metadata to the metadata_cb as
OSSL_PARAM(3) parameters.
The decoder 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 DECODER implementation may be part of a chain, where data is passed
from one to the next. For example, there may be an implementation to
decode an object from PEM to DER, and another one that decodes DER to a
provider-native object.
The last decoding step in the decoding chain is usually supposed to
create a provider-native object referenced by an object reference. To
import that object into a different provider the
OSSL_FUNC_decoder_export_object() can be called as the final step of the
decoding process.
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_decoder_decode() has these:
typedef int
(OSSL_FUNC_decoder_decode_fn)(void *ctx, OSSL_CORE_BIO *in,
int selection,
OSSL_CALLBACK *data_cb, void *data_cbarg,
OSSL_PASSPHRASE_CALLBACK *cb, void *cbarg);
static ossl_inline OSSL_FUNC_decoder_decode_fn*
OSSL_FUNC_decoder_decode(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_decoder_get_params OSSL_FUNC_DECODER_GET_PARAMS
OSSL_FUNC_decoder_gettable_params OSSL_FUNC_DECODER_GETTABLE_PARAMS
OSSL_FUNC_decoder_newctx OSSL_FUNC_DECODER_NEWCTX
OSSL_FUNC_decoder_freectx OSSL_FUNC_DECODER_FREECTX
OSSL_FUNC_decoder_set_ctx_params OSSL_FUNC_DECODER_SET_CTX_PARAMS
OSSL_FUNC_decoder_settable_ctx_params OSSL_FUNC_DECODER_SETTABLE_CTX_PARAMS
OSSL_FUNC_decoder_does_selection OSSL_FUNC_DECODER_DOES_SELECTION
OSSL_FUNC_decoder_decode OSSL_FUNC_DECODER_DECODE
OSSL_FUNC_decoder_export_object OSSL_FUNC_DECODER_EXPORT_OBJECT
Names and properties
The name of an implementation should match the target type of object it
decodes. For example, an implementation that decodes an RSA key should
be named "RSA". Likewise, an implementation that decodes DER data from
PEM input 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:
input
This property is used to specify what format of input the
implementation can decode.
This property is mandatory.
OpenSSL providers recognize the following input types:
pem An implementation with that input type decodes PEM formatted
data.
der An implementation with that input type decodes DER formatted
data.
msblob
An implementation with that input type decodes MSBLOB formatted
data.
pvk An implementation with that input type decodes PVK formatted
data.
structure
This property is used to specify the structure that the decoded data
is expected to have.
This property is optional.
Structures currently recognised by built-in decoders:
"type-specific"
Type specific structure.
"pkcs8"
Structure according to the PKCS#8 specification.
"SubjectPublicKeyInfo"
Encoding of public keys according to the Subject Public Key Info
of RFC 5280.
The possible values of both these properties is open ended. A provider
may very well specify input 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 decoded, 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
to be decoded. 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 - e.g.,
OSSL_KEYMGMT_SELECT_PRIVATE_KEY if the object to be decoded is supposed
to contain private key components.
OSSL_FUNC_decoder_does_selection() should tell if a particular
implementation supports any of the combinations given by selection.
Context functions
OSSL_FUNC_decoder_newctx() returns a context to be used with the rest of
the functions.
OSSL_FUNC_decoder_freectx() frees the given ctx as created by
OSSL_FUNC_decoder_newctx().
OSSL_FUNC_decoder_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_decoder_settable_ctx_params() returns a constant OSSL_PARAM(3)
array describing the parameters that OSSL_FUNC_decoder_set_ctx_params()
can handle.
See OSSL_PARAM(3) for further details on the parameters structure used
by OSSL_FUNC_decoder_set_ctx_params() and
OSSL_FUNC_decoder_settable_ctx_params().
Export function
When a provider-native object is created by a decoder it would be
unsuitable for direct use with a foreign provider. The export function
allows for exporting the object into that foreign provider if the
foreign provider supports the type of the object and provides an import
function.
OSSL_FUNC_decoder_export_object() should export the object of size
objref_sz referenced by objref as an OSSL_PARAM(3) array and pass that
into the export_cb as well as the given export_cbarg.
Decoding functions
OSSL_FUNC_decoder_decode() should decode the data as read from the
OSSL_CORE_BIO in to produce decoded data or an object to be passed as
reference in an OSSL_PARAM(3) array along with possible other metadata
that was decoded from the input. This OSSL_PARAM(3) array is then passed
to the data_cb callback. The selection bits, if relevant, should
determine what the input data should contain. The decoding 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.
It's important to understand that the return value from this function is
interpreted as follows:
True (1)
This means "carry on the decoding process", and is meaningful even
though this function couldn't decode the input into anything,
because there may be another decoder implementation that can decode
it into something.
The data_cb callback should never be called when this function can't
decode the input into anything.
False (0)
This means "stop the decoding process", and is meaningful when the
input could be decoded into some sort of object that this function
understands, but further treatment of that object results into
errors that won't be possible for some other decoder implementation
to get a different result.
The conditions to stop the decoding process are at the discretion of the
implementation.
Decoder operation parameters
There are currently no operation parameters currently recognised by the
built-in decoders.
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_decoder_newctx() returns a pointer to a context, or NULL on
failure.
OSSL_FUNC_decoder_set_ctx_params() returns 1, unless a recognised
parameter was invalid or caused an error, for which 0 is returned.
OSSL_FUNC_decoder_settable_ctx_params() returns a pointer to an array of
constant OSSL_PARAM(3) elements.
OSSL_FUNC_decoder_does_selection() returns 1 if the decoder
implementation supports any of the selection bits, otherwise 0.
OSSL_FUNC_decoder_decode() returns 1 to signal that the decoding process
should continue, or 0 to signal that it should stop.
SEE ALSO
provider(7)
HISTORY
The DECODER 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-DECODER(7SSL)
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