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PROVIDER-DECODER(7ossl)              OpenSSL             PROVIDER-DECODER(7ossl)





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 */
        void *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 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 2019-2021 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>.



3.0.8                              2023-02-07            PROVIDER-DECODER(7ossl)

openssl 3.0.8 - Generated Wed Feb 8 12:29:21 CST 2023
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