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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_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
LIBRARY
libcrypto, -lcrypto
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>.
3.0.12 2023-10-25 EVP_KDF(3)