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(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.

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 2019-2024 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>.