PROVIDER-MAC(7)

NAME
provider-mac - The mac library <-> provider functions

SYNOPSIS
 #include <openssl/core_numbers.h>
 #include <openssl/core_names.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.
  */

 /* Context management */
 void *OP_mac_newctx(void *provctx);
 void OP_mac_freectx(void *mctx);
 void *OP_mac_dupctx(void *src);

 /* Encryption/decryption */
 int OP_mac_init(void *mctx);
 int OP_mac_update(void *mctx, const unsigned char *in, size_t inl);
 int OP_mac_final(void *mctx, unsigned char *out, size_t *outl, size_t outsize);

 /* MAC parameter descriptors */
 const OSSL_PARAM *OP_mac_get_params(void);
 const OSSL_PARAM *OP_mac_get_ctx_params(void);
 const OSSL_PARAM *OP_mac_set_ctx_params(void);

 /* MAC parameters */
 int OP_mac_get_params(OSSL_PARAM params[]);
 int OP_mac_get_ctx_params(void *mctx, OSSL_PARAM params[]);
 int OP_mac_set_ctx_params(void *mctx, const OSSL_PARAM params[]);

DESCRIPTION
This documentation is primarily aimed at provider authors. See provider(7) for further information.

The MAC operation enables providers to implement mac algorithms and make them available to applications via the API functions EVP_MAC_init(3), EVP_MAC_update(3) and EVP_MAC_final(3).

All "functions" mentioned here are passed as function pointers between libcrypto and the provider in OSSL_DISPATCH arrays via OSSL_ALGORITHM 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_{name}_fn, and a helper function to retrieve the function pointer from an OSSL_DISPATCH element named OSSL_get_{name}. For example, the "function" OP_mac_newctx() has these:

 typedef void *(OSSL_OP_mac_newctx_fn)(void *provctx);
 static ossl_inline OSSL_OP_mac_newctx_fn
     OSSL_get_OP_mac_newctx(const OSSL_DISPATCH *opf);

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

 OP_mac_newctx               OSSL_FUNC_MAC_NEWCTX
 OP_mac_freectx              OSSL_FUNC_MAC_FREECTX
 OP_mac_dupctx               OSSL_FUNC_MAC_DUPCTX

 OP_mac_init                 OSSL_FUNC_MAC_INIT
 OP_mac_update               OSSL_FUNC_MAC_UPDATE
 OP_mac_final                OSSL_FUNC_MAC_FINAL

 OP_mac_get_params           OSSL_FUNC_MAC_GET_PARAMS
 OP_mac_get_ctx_params       OSSL_FUNC_MAC_GET_CTX_PARAMS
 OP_mac_set_ctx_params       OSSL_FUNC_MAC_SET_CTX_PARAMS

 OP_mac_gettable_params      OSSL_FUNC_MAC_GETTABLE_PARAMS
 OP_mac_gettable_ctx_params  OSSL_FUNC_MAC_GETTABLE_CTX_PARAMS
 OP_mac_settable_ctx_params  OSSL_FUNC_MAC_SETTABLE_CTX_PARAMS

A mac algorithm implementation may not implement all of these functions. In order to be a consistent set of functions, at least the following functions must be implemented: OP_mac_newctx(), OP_mac_freectx(), OP_mac_init(), OP_mac_update(), OP_mac_final(). All other functions are optional.

  Context Management Functions
OP_mac_newctx() should create and return a pointer to a provider side structure for holding context information during a mac operation. A pointer to this context will be passed back in a number of the other mac operation function calls. The parameter provctx is the provider context generated during provider initialisation (see provider(7)).

OP_mac_freectx() is passed a pointer to the provider side mac context in the mctx parameter. If it receives NULL as mctx value, it should not do anything other than return. This function should free any resources associated with that context.

OP_mac_dupctx() should duplicate the provider side mac context in the mctx parameter and return the duplicate copy.

  Encryption/Decryption Functions
OP_mac_init() initialises a mac operation given a newly created provider side mac context in the mctx parameter.

OP_mac_update() is called to supply data for MAC computation of a previously initialised mac operation. The mctx parameter contains a pointer to a previously initialised provider side context. OP_mac_update() may be called multiple times for a single mac operation.

OP_mac_final() completes the MAC computation started through previous OP_mac_init() and OP_mac_update() calls. The mctx parameter contains a pointer to the provider side context. The resulting MAC should be written to out and the amount of data written to *outl, which should not exceed outsize bytes. The same expectations apply to outsize as documented for EVP_MAC_final(3).

  Mac Parameters
See OSSL_PARAM(3) for further details on the parameters structure used by these functions.

OP_mac_get_params() gets details of parameter values associated with the provider algorithm and stores them in params.

OP_mac_set_ctx_params() sets mac parameters associated with the given provider side mac context mctx to params. Any parameter settings are additional to any that were previously set.

OP_mac_get_ctx_params() gets details of currently set parameter values associated with the given provider side mac context mctx and stores them in params.

OP_mac_gettable_params(), OP_mac_gettable_ctx_params(), and OP_mac_settable_ctx_params() all return constant OSSL_PARAM arrays as descriptors of the parameters that OP_mac_get_params(), OP_mac_get_ctx_params(), and OP_mac_set_ctx_params() can handle, respectively.

Parameters currently recognised by built-in macs are as follows. Not all parameters are relevant to, or are understood by all macs:

"key" (OSSL_MAC_PARAM_KEY) <octet string>
    Sets the key in the associated MAC ctx.

"iv" (OSSL_MAC_PARAM_IV) <octet string>
    Sets the IV of the underlying cipher, when applicable.

"custom" (OSSL_MAC_PARAM_CUSTOM) <UTF8 string>
    Sets the custom string in the associated MAC ctx.

"salt" (OSSL_MAC_PARAM_SALT) <octet string>
    Sets the salt of the underlying cipher, when applicable.

"xof" (OSSL_MAC_PARAM_BLOCK_XOF) <integer>
    Sets XOF mode in the associated MAC ctx. 0 means no XOF mode, 1 means XOF mode.

"flags" (OSSL_MAC_PARAM_FLAGS) <integer>
    Gets flags associated with the MAC.

"cipher" (OSSL_MAC_PARAM_CIPHER) <UTF8 string>
"digest" (OSSL_MAC_PARAM_DIGEST) <UTF8 string>
    Sets the name of the underlying cipher or digest to be used. It must name a suitable algorithm for the MAC that's being used.

"properties" (OSSL_MAC_PARAM_PROPERTIES) <UTF8 string>
    Sets the properties to be queried when trying to fetch the underlying algorithm. This must be given together with the algorithm naming parameter to be considered valid.

"size" (OSSL_MAC_PARAM_SIZE) <integer>
    Can be used to get the resulting MAC size.

    With some MAC algorithms, it can also be used to set the size that the resulting MAC should have. Allowable sizes are decided within each implementation.

RETURN VALUES
OP_mac_newctx() and OP_mac_dupctx() should return the newly created provider side mac context, or NULL on failure.

OP_mac_init(), OP_mac_update(), OP_mac_final(), OP_mac_get_params(), OP_mac_get_ctx_params() and OP_mac_set_ctx_params() should return 1 for success or 0 on error.

OP_mac_gettable_params(), OP_mac_gettable_ctx_params() and OP_mac_settable_ctx_params() should return a constant OSSL_PARAM array, or NULL if none is offered.

SEE ALSO
provider(7)

HISTORY
The provider MAC interface was introduced in OpenSSL 3.0.

COPYRIGHT
Copyright 2019 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>.