provider-encoder - The OSSL_ENCODER library <-> provider functions
#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);
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
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 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.
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.
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().
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().
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.
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.
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.
provider(7)
The ENCODER interface was introduced in OpenSSL 3.0.
Copyright 2019-2021 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>.