Provided by: libssl-doc_3.0.13-0ubuntu3.4_all 
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_get0_provider, EVP_KDF_CTX_kdf, EVP_KDF_is_a,
EVP_KDF_get0_name, EVP_KDF_names_do_all, EVP_KDF_get0_description, EVP_KDF_CTX_get_params,
EVP_KDF_CTX_set_params, EVP_KDF_do_all_provided, EVP_KDF_get_params,
EVP_KDF_gettable_params, EVP_KDF_gettable_ctx_params, EVP_KDF_settable_ctx_params,
EVP_KDF_CTX_gettable_params, EVP_KDF_CTX_settable_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,
const OSSL_PARAM params[]);
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_is_a(const EVP_KDF *kdf, const char *name);
const char *EVP_KDF_get0_name(const EVP_KDF *kdf);
const char *EVP_KDF_get0_description(const EVP_KDF *kdf);
const OSSL_PROVIDER *EVP_KDF_get0_provider(const EVP_KDF *kdf);
void EVP_KDF_do_all_provided(OSSL_LIB_CTX *libctx,
void (*fn)(EVP_KDF *kdf, void *arg),
void *arg);
int 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_PARAM *EVP_KDF_CTX_gettable_params(const EVP_KDF *kdf);
const OSSL_PARAM *EVP_KDF_CTX_settable_params(const EVP_KDF *kdf);
const OSSL_PROVIDER *EVP_KDF_get0_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 either by passing them as part of the EVP_KDF_derive() call or
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 "ALGORITHM FETCHING" in crypto(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() processes any parameters in Params and then 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() returns an OSSL_PARAM(3) array that describes the retrievable
and settable parameters. EVP_KDF_gettable_params() returns parameters that can be used
with EVP_KDF_get_params().
EVP_KDF_gettable_ctx_params() and EVP_KDF_CTX_gettable_params() return constant
OSSL_PARAM(3) arrays that describe the retrievable parameters that can be used with
EVP_KDF_CTX_get_params(). EVP_KDF_gettable_ctx_params() returns the parameters that can
be retrieved from the algorithm, whereas EVP_KDF_CTX_gettable_params() returns the
parameters that can be retrieved in the context's current state.
EVP_KDF_settable_ctx_params() and EVP_KDF_CTX_settable_params() return constant
OSSL_PARAM(3) arrays that describe the settable parameters that can be used with
EVP_KDF_CTX_set_params(). EVP_KDF_settable_ctx_params() returns the parameters that can
be retrieved from the algorithm, whereas EVP_KDF_CTX_settable_params() returns the
parameters that can be retrieved in the context's current state.
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_get0_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_get0_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.
EVP_KDF_get0_description() returns a description of the kdf, meant for display and human
consumption. The description is at the discretion of the kdf implementation.
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 non-secret unique cryptographic 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.
"info" (OSSL_KDF_PARAM_INFO) <octet string>
Some KDF implementations, such as EVP_KDF-HKDF(7), take an 'info' parameter for
binding the derived key material to application- and context-specific information.
This parameter sets the info, fixed info, other info or shared info argument. You can
specify this parameter multiple times, and each instance will be concatenated to form
the final value.
"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_get0_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_get0_name() returns the name of the KDF, or NULL on error.
EVP_KDF_names_do_all() returns 1 if the callback was called for all names. A return value
of 0 means that the callback was not called for any names.
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.
NOTES
The KDF life-cycle is described in life_cycle-kdf(7). In the future, the transitions
described there will be enforced. When this is done, it will not be considered a breaking
change to the API.
SEE ALSO
"Key Derivation Function (KDF)" in OSSL_PROVIDER-default(7), life_cycle-kdf(7).
HISTORY
This functionality was added in OpenSSL 3.0.
COPYRIGHT
Copyright 2019-2023 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>.