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EVP_KDF(3)			    OpenSSL			    EVP_KDF(3)

NAME
       EVP_KDF,	EVP_KDF_fetch, EVP_KDF_free, EVP_KDF_up_ref, EVP_KDF_CTX,
       EVP_KDF_CTX_new,	EVP_KDF_CTX_free, EVP_KDF_CTX_dup, EVP_KDF_CTX_reset,
       EVP_KDF_derive, EVP_KDF_CTX_get_kdf_size, EVP_KDF_provider,
       EVP_KDF_CTX_kdf,	EVP_KDF_is_a, EVP_KDF_number, EVP_KDF_name,
       EVP_KDF_names_do_all, EVP_KDF_CTX_get_params, EVP_KDF_CTX_set_params,
       EVP_KDF_do_all_provided,	EVP_KDF_get_params,
       EVP_KDF_gettable_ctx_params, EVP_KDF_settable_ctx_params,
       EVP_KDF_gettable_params - EVP KDF routines

SYNOPSIS
	#include <openssl/kdf.h>

	typedef	struct evp_kdf_st EVP_KDF;
	typedef	struct evp_kdf_ctx_st EVP_KDF_CTX;

	EVP_KDF_CTX *EVP_KDF_CTX_new(const EVP_KDF *kdf);
	const EVP_KDF *EVP_KDF_CTX_kdf(EVP_KDF_CTX *ctx);
	void EVP_KDF_CTX_free(EVP_KDF_CTX *ctx);
	EVP_KDF_CTX *EVP_KDF_CTX_dup(const EVP_KDF_CTX *src);
	void EVP_KDF_CTX_reset(EVP_KDF_CTX *ctx);
	size_t EVP_KDF_CTX_get_kdf_size(EVP_KDF_CTX *ctx);
	int EVP_KDF_derive(EVP_KDF_CTX *ctx, unsigned char *key, size_t	keylen);
	int EVP_KDF_up_ref(EVP_KDF *kdf);
	void EVP_KDF_free(EVP_KDF *kdf);
	EVP_KDF	*EVP_KDF_fetch(OSSL_LIB_CTX *libctx, const char	*algorithm,
			       const char *properties);
	int EVP_KDF_number(const EVP_KDF *kdf);
	int EVP_KDF_is_a(const EVP_KDF *kdf, const char	*name);
	const char *EVP_KDF_name(const EVP_KDF *kdf);
	const OSSL_PROVIDER *EVP_KDF_provider(const EVP_KDF *kdf);
	void EVP_KDF_do_all_provided(OSSL_LIB_CTX *libctx,
				     void (*fn)(EVP_KDF	*kdf, void *arg),
				     void *arg);
	void EVP_KDF_names_do_all(const	EVP_KDF	*kdf,
				  void (*fn)(const char	*name, void *data),
				  void *data);
	int EVP_KDF_get_params(EVP_KDF *kdf, OSSL_PARAM	params[]);
	int EVP_KDF_CTX_get_params(EVP_KDF_CTX *ctx, OSSL_PARAM	params[]);
	int EVP_KDF_CTX_set_params(EVP_KDF_CTX *ctx, const OSSL_PARAM params[]);
	const OSSL_PARAM *EVP_KDF_gettable_params(const	EVP_KDF	*kdf);
	const OSSL_PARAM *EVP_KDF_gettable_ctx_params(const EVP_KDF *kdf);
	const OSSL_PARAM *EVP_KDF_settable_ctx_params(const EVP_KDF *kdf);
	const OSSL_PROVIDER *EVP_KDF_provider(const EVP_KDF *kdf);

DESCRIPTION
       The EVP KDF routines are	a high-level interface to Key Derivation
       Function	algorithms and should be used instead of algorithm-specific
       functions.

       After creating a	EVP_KDF_CTX for	the required algorithm using
       EVP_KDF_CTX_new(), inputs to the	algorithm are supplied using calls to
       EVP_KDF_CTX_set_params()	before calling EVP_KDF_derive()	to derive the
       key.

   Types
       EVP_KDF is a type that holds the	implementation of a KDF.

       EVP_KDF_CTX is a	context	type that holds	the algorithm inputs.

   Algorithm implementation fetching
       EVP_KDF_fetch() fetches an implementation of a KDF algorithm, given a
       library context libctx and a set	of properties.	See "Fetching
       algorithms" in provider(7) for further information.

       See "Key	Derivation Function (KDF)" in OSSL_PROVIDER-default(7) for the
       lists of	algorithms supported by	the default provider.

       The returned value must eventually be freed with	EVP_KDF_free(3).

       EVP_KDF_up_ref()	increments the reference count of an already fetched
       KDF.

       EVP_KDF_free() frees a fetched algorithm.  NULL is a valid parameter,
       for which this function is a no-op.

   Context manipulation	functions
       EVP_KDF_CTX_new() creates a new context for the KDF implementation kdf.

       EVP_KDF_CTX_free() frees	up the context ctx.  If	ctx is NULL, nothing
       is done.

       EVP_KDF_CTX_kdf() returns the EVP_KDF associated	with the context ctx.

   Computing functions
       EVP_KDF_CTX_reset() resets the context to the default state as if the
       context had just	been created.

       EVP_KDF_derive()	derives	keylen bytes of	key material and places	it in
       the key buffer.	If the algorithm produces a fixed amount of output
       then an error will occur	unless the keylen parameter is equal to	that
       output size, as returned	by EVP_KDF_CTX_get_kdf_size().

       EVP_KDF_get_params() retrieves details about the	implementation kdf.
       The set of parameters given with	params determine exactly what
       parameters should be retrieved.	Note that a parameter that is unknown
       in the underlying context is simply ignored.

       EVP_KDF_CTX_get_params()	retrieves chosen parameters, given the context
       ctx and its underlying context.	The set	of parameters given with
       params determine	exactly	what parameters	should be retrieved.  Note
       that a parameter	that is	unknown	in the underlying context is simply
       ignored.

       EVP_KDF_CTX_set_params()	passes chosen parameters to the	underlying
       context,	given a	context	ctx.  The set of parameters given with params
       determine exactly what parameters are passed down.  Note	that a
       parameter that is unknown in the	underlying context is simply ignored.
       Also, what happens when a needed	parameter isn't	passed down is defined
       by the implementation.

       EVP_KDF_gettable_params(), EVP_KDF_gettable_ctx_params()	and
       EVP_KDF_settable_ctx_params() get a constant OSSL_PARAM array that
       describes the retrievable and settable parameters, i.e. parameters that
       can be used with	EVP_KDF_get_params(), EVP_KDF_CTX_get_params() and
       EVP_KDF_CTX_set_params(), respectively.	See OSSL_PARAM(3) for the use
       of OSSL_PARAM as	parameter descriptor.

   Information functions
       EVP_KDF_CTX_get_kdf_size() returns the output size if the algorithm
       produces	a fixed	amount of output and SIZE_MAX otherwise.  If an	error
       occurs then 0 is	returned.  For some algorithms an error	may result if
       input parameters	necessary to calculate a fixed output size have	not
       yet been	supplied.

       EVP_KDF_is_a() returns 1	if kdf is an implementation of an algorithm
       that's identifiable with	name, otherwise	0.

       EVP_KDF_provider() returns the provider that holds the implementation
       of the given kdf.

       EVP_KDF_do_all_provided() traverses all KDF implemented by all
       activated providers in the given	library	context	libctx,	and for	each
       of the implementations, calls the given function	fn with	the
       implementation method and the given arg as argument.

       EVP_KDF_number()	returns	the internal dynamic number assigned to	kdf.

       EVP_KDF_name() return the name of the given KDF.	 For fetched KDFs with
       multiple	names, only one	of them	is returned; it's recommended to use
       EVP_KDF_names_do_all() instead.

       EVP_KDF_names_do_all() traverses	all names for kdf, and calls fn	with
       each name and data.

PARAMETERS
       The standard parameter names are:

       "pass" (OSSL_KDF_PARAM_PASSWORD)	<octet string>
	   Some	KDF implementations require a password.	 For those KDF
	   implementations that	support	it, this parameter sets	the password.

       "salt" (OSSL_KDF_PARAM_SALT) <octet string>
	   Some	KDF implementations can	take a salt.  For those	KDF
	   implementations that	support	it, this parameter sets	the salt.

	   The default value, if any, is implementation	dependent.

       "iter" (OSSL_KDF_PARAM_ITER) <unsigned integer>
	   Some	KDF implementations require an iteration count.	 For those KDF
	   implementations that	support	it, this parameter sets	the iteration
	   count.

	   The default value, if any, is implementation	dependent.

       "properties" (OSSL_KDF_PARAM_PROPERTIES)	<UTF8 string>
       "mac" (OSSL_KDF_PARAM_MAC) <UTF8	string>
       "digest"	(OSSL_KDF_PARAM_DIGEST)	<UTF8 string>
       "cipher"	(OSSL_KDF_PARAM_CIPHER)	<UTF8 string>
	   For KDF implementations that	use an underlying computation MAC,
	   digest or cipher, these parameters set what the algorithm should
	   be.

	   The value is	always the name	of the intended	algorithm, or the
	   properties.

	   Note	that not all algorithms	may support all	possible underlying
	   implementations.

       "key" (OSSL_KDF_PARAM_KEY) <octet string>
	   Some	KDF implementations require a key.  For	those KDF
	   implementations that	support	it, this octet string parameter	sets
	   the key.

       "maclen"	(OSSL_KDF_PARAM_MAC_SIZE) <unsigned integer>
	   Used	by implementations that	use a MAC with a variable output size
	   (KMAC).  For	those KDF implementations that support it, this
	   parameter sets the MAC output size.

	   The default value, if any, is implementation	dependent.  The	length
	   must	never exceed what can be given with a size_t.

       "maxmem_bytes" (OSSL_KDF_PARAM_SCRYPT_MAXMEM) <unsigned integer>
	   Memory-hard password-based KDF algorithms, such as scrypt, use an
	   amount of memory that depends on the	load factors provided as
	   input.  For those KDF implementations that support it, this
	   uint64_t parameter sets an upper limit on the amount	of memory that
	   may be consumed while performing a key derivation.  If this memory
	   usage limit is exceeded because the load factors are	chosen too
	   high, the key derivation will fail.

	   The default value is	implementation dependent.  The memory size
	   must	never exceed what can be given with a size_t.

RETURN VALUES
       EVP_KDF_fetch() returns a pointer to a newly fetched EVP_KDF, or	NULL
       if allocation failed.

       EVP_KDF_provider() returns a pointer to the provider for	the KDF, or
       NULL on error.

       EVP_KDF_up_ref()	returns	1 on success, 0	on error.

       EVP_KDF_CTX_new() returns either	the newly allocated EVP_KDF_CTX
       structure or NULL if an error occurred.

       EVP_KDF_CTX_free() and EVP_KDF_CTX_reset() do not return	a value.

       EVP_KDF_CTX_get_kdf_size() returns the output size.  SIZE_MAX is
       returned	to indicate that the algorithm produces	a variable amount of
       output; 0 to indicate failure.

       EVP_KDF_name() returns the name of the KDF, or NULL on error.

       The remaining functions return 1	for success and	0 or a negative	value
       for failure.  In	particular, a return value of -2 indicates the
       operation is not	supported by the KDF algorithm.

SEE ALSO
       "Key Derivation Function	(KDF)" in OSSL_PROVIDER-default(7)

HISTORY
       This functionality was added to OpenSSL 3.0.

COPYRIGHT
       Copyright 2019-2020 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>.

3.0.0-alpha12			  2021-02-18			    EVP_KDF(3)

NAME | SYNOPSIS | DESCRIPTION | PARAMETERS | RETURN VALUES | SEE ALSO | HISTORY | COPYRIGHT

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