1EVP_KDF(3ossl)                      OpenSSL                     EVP_KDF(3ossl)
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NAME

6       EVP_KDF, EVP_KDF_fetch, EVP_KDF_free, EVP_KDF_up_ref, EVP_KDF_CTX,
7       EVP_KDF_CTX_new, EVP_KDF_CTX_free, EVP_KDF_CTX_dup, EVP_KDF_CTX_reset,
8       EVP_KDF_derive, EVP_KDF_CTX_get_kdf_size, EVP_KDF_get0_provider,
9       EVP_KDF_CTX_kdf, EVP_KDF_is_a, EVP_KDF_get0_name, EVP_KDF_names_do_all,
10       EVP_KDF_get0_description, EVP_KDF_CTX_get_params,
11       EVP_KDF_CTX_set_params, EVP_KDF_do_all_provided, EVP_KDF_get_params,
12       EVP_KDF_gettable_params, EVP_KDF_gettable_ctx_params,
13       EVP_KDF_settable_ctx_params, EVP_KDF_CTX_gettable_params,
14       EVP_KDF_CTX_settable_params - EVP KDF routines
15

SYNOPSIS

17        #include <openssl/kdf.h>
18
19        typedef struct evp_kdf_st EVP_KDF;
20        typedef struct evp_kdf_ctx_st EVP_KDF_CTX;
21
22        EVP_KDF_CTX *EVP_KDF_CTX_new(const EVP_KDF *kdf);
23        const EVP_KDF *EVP_KDF_CTX_kdf(EVP_KDF_CTX *ctx);
24        void EVP_KDF_CTX_free(EVP_KDF_CTX *ctx);
25        EVP_KDF_CTX *EVP_KDF_CTX_dup(const EVP_KDF_CTX *src);
26        void EVP_KDF_CTX_reset(EVP_KDF_CTX *ctx);
27        size_t EVP_KDF_CTX_get_kdf_size(EVP_KDF_CTX *ctx);
28        int EVP_KDF_derive(EVP_KDF_CTX *ctx, unsigned char *key, size_t keylen,
29                           const OSSL_PARAM params[]);
30        int EVP_KDF_up_ref(EVP_KDF *kdf);
31        void EVP_KDF_free(EVP_KDF *kdf);
32        EVP_KDF *EVP_KDF_fetch(OSSL_LIB_CTX *libctx, const char *algorithm,
33                               const char *properties);
34        int EVP_KDF_is_a(const EVP_KDF *kdf, const char *name);
35        const char *EVP_KDF_get0_name(const EVP_KDF *kdf);
36        const char *EVP_KDF_get0_description(const EVP_KDF *kdf);
37        const OSSL_PROVIDER *EVP_KDF_get0_provider(const EVP_KDF *kdf);
38        void EVP_KDF_do_all_provided(OSSL_LIB_CTX *libctx,
39                                     void (*fn)(EVP_KDF *kdf, void *arg),
40                                     void *arg);
41        int EVP_KDF_names_do_all(const EVP_KDF *kdf,
42                                 void (*fn)(const char *name, void *data),
43                                 void *data);
44        int EVP_KDF_get_params(EVP_KDF *kdf, OSSL_PARAM params[]);
45        int EVP_KDF_CTX_get_params(EVP_KDF_CTX *ctx, OSSL_PARAM params[]);
46        int EVP_KDF_CTX_set_params(EVP_KDF_CTX *ctx, const OSSL_PARAM params[]);
47        const OSSL_PARAM *EVP_KDF_gettable_params(const EVP_KDF *kdf);
48        const OSSL_PARAM *EVP_KDF_gettable_ctx_params(const EVP_KDF *kdf);
49        const OSSL_PARAM *EVP_KDF_settable_ctx_params(const EVP_KDF *kdf);
50        const OSSL_PARAM *EVP_KDF_CTX_gettable_params(const EVP_KDF *kdf);
51        const OSSL_PARAM *EVP_KDF_CTX_settable_params(const EVP_KDF *kdf);
52        const OSSL_PROVIDER *EVP_KDF_get0_provider(const EVP_KDF *kdf);
53

DESCRIPTION

55       The EVP KDF routines are a high-level interface to Key Derivation
56       Function algorithms and should be used instead of algorithm-specific
57       functions.
58
59       After creating a EVP_KDF_CTX for the required algorithm using
60       EVP_KDF_CTX_new(), inputs to the algorithm are supplied either by
61       passing them as part of the EVP_KDF_derive() call or using calls to
62       EVP_KDF_CTX_set_params() before calling EVP_KDF_derive() to derive the
63       key.
64
65   Types
66       EVP_KDF is a type that holds the implementation of a KDF.
67
68       EVP_KDF_CTX is a context type that holds the algorithm inputs.
69
70   Algorithm implementation fetching
71       EVP_KDF_fetch() fetches an implementation of a KDF algorithm, given a
72       library context libctx and a set of properties.  See "ALGORITHM
73       FETCHING" in crypto(7) for further information.
74
75       See "Key Derivation Function (KDF)" in OSSL_PROVIDER-default(7) for the
76       lists of algorithms supported by the default provider.
77
78       The returned value must eventually be freed with EVP_KDF_free(3).
79
80       EVP_KDF_up_ref() increments the reference count of an already fetched
81       KDF.
82
83       EVP_KDF_free() frees a fetched algorithm.  NULL is a valid parameter,
84       for which this function is a no-op.
85
86   Context manipulation functions
87       EVP_KDF_CTX_new() creates a new context for the KDF implementation kdf.
88
89       EVP_KDF_CTX_free() frees up the context ctx.  If ctx is NULL, nothing
90       is done.
91
92       EVP_KDF_CTX_kdf() returns the EVP_KDF associated with the context ctx.
93
94   Computing functions
95       EVP_KDF_CTX_reset() resets the context to the default state as if the
96       context had just been created.
97
98       EVP_KDF_derive() processes any parameters in Params and then derives
99       keylen bytes of key material and places it in the key buffer.  If the
100       algorithm produces a fixed amount of output then an error will occur
101       unless the keylen parameter is equal to that output size, as returned
102       by EVP_KDF_CTX_get_kdf_size().
103
104       EVP_KDF_get_params() retrieves details about the implementation kdf.
105       The set of parameters given with params determine exactly what
106       parameters should be retrieved.  Note that a parameter that is unknown
107       in the underlying context is simply ignored.
108
109       EVP_KDF_CTX_get_params() retrieves chosen parameters, given the context
110       ctx and its underlying context.  The set of parameters given with
111       params determine exactly what parameters should be retrieved.  Note
112       that a parameter that is unknown in the underlying context is simply
113       ignored.
114
115       EVP_KDF_CTX_set_params() passes chosen parameters to the underlying
116       context, given a context ctx.  The set of parameters given with params
117       determine exactly what parameters are passed down.  Note that a
118       parameter that is unknown in the underlying context is simply ignored.
119       Also, what happens when a needed parameter isn't passed down is defined
120       by the implementation.
121
122       EVP_KDF_gettable_params() returns an OSSL_PARAM array that describes
123       the retrievable and settable parameters.  EVP_KDF_gettable_params()
124       returns parameters that can be used with EVP_KDF_get_params().  See
125       OSSL_PARAM(3) for the use of OSSL_PARAM as a parameter descriptor.
126
127       EVP_KDF_gettable_ctx_params() and EVP_KDF_CTX_gettable_params() return
128       constant OSSL_PARAM arrays that describe the retrievable parameters
129       that can be used with EVP_KDF_CTX_get_params().
130       EVP_KDF_gettable_ctx_params() returns the parameters that can be
131       retrieved from the algorithm, whereas EVP_KDF_CTX_gettable_params()
132       returns the parameters that can be retrieved in the context's current
133       state.  See OSSL_PARAM(3) for the use of OSSL_PARAM as a parameter
134       descriptor.
135
136       EVP_KDF_settable_ctx_params() and EVP_KDF_CTX_settable_params() return
137       constant OSSL_PARAM arrays that describe the settable parameters that
138       can be used with EVP_KDF_CTX_set_params().
139       EVP_KDF_settable_ctx_params() returns the parameters that can be
140       retrieved from the algorithm, whereas EVP_KDF_CTX_settable_params()
141       returns the parameters that can be retrieved in the context's current
142       state.  See OSSL_PARAM(3) for the use of OSSL_PARAM as a parameter
143       descriptor.
144
145   Information functions
146       EVP_KDF_CTX_get_kdf_size() returns the output size if the algorithm
147       produces a fixed amount of output and SIZE_MAX otherwise.  If an error
148       occurs then 0 is returned.  For some algorithms an error may result if
149       input parameters necessary to calculate a fixed output size have not
150       yet been supplied.
151
152       EVP_KDF_is_a() returns 1 if kdf is an implementation of an algorithm
153       that's identifiable with name, otherwise 0.
154
155       EVP_KDF_get0_provider() returns the provider that holds the
156       implementation of the given kdf.
157
158       EVP_KDF_do_all_provided() traverses all KDF implemented by all
159       activated providers in the given library context libctx, and for each
160       of the implementations, calls the given function fn with the
161       implementation method and the given arg as argument.
162
163       EVP_KDF_get0_name() return the name of the given KDF.  For fetched KDFs
164       with multiple names, only one of them is returned; it's recommended to
165       use EVP_KDF_names_do_all() instead.
166
167       EVP_KDF_names_do_all() traverses all names for kdf, and calls fn with
168       each name and data.
169
170       EVP_KDF_get0_description() returns a description of the kdf, meant for
171       display and human consumption.  The description is at the discretion of
172       the kdf implementation.
173

PARAMETERS

175       The standard parameter names are:
176
177       "pass" (OSSL_KDF_PARAM_PASSWORD) <octet string>
178           Some KDF implementations require a password.  For those KDF
179           implementations that support it, this parameter sets the password.
180
181       "salt" (OSSL_KDF_PARAM_SALT) <octet string>
182           Some KDF implementations can take a salt.  For those KDF
183           implementations that support it, this parameter sets the salt.
184
185           The default value, if any, is implementation dependent.
186
187       "iter" (OSSL_KDF_PARAM_ITER) <unsigned integer>
188           Some KDF implementations require an iteration count.  For those KDF
189           implementations that support it, this parameter sets the iteration
190           count.
191
192           The default value, if any, is implementation dependent.
193
194       "properties" (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>
195       "mac" (OSSL_KDF_PARAM_MAC) <UTF8 string>
196       "digest" (OSSL_KDF_PARAM_DIGEST) <UTF8 string>
197       "cipher" (OSSL_KDF_PARAM_CIPHER) <UTF8 string>
198           For KDF implementations that use an underlying computation MAC,
199           digest or cipher, these parameters set what the algorithm should
200           be.
201
202           The value is always the name of the intended algorithm, or the
203           properties.
204
205           Note that not all algorithms may support all possible underlying
206           implementations.
207
208       "key" (OSSL_KDF_PARAM_KEY) <octet string>
209           Some KDF implementations require a key.  For those KDF
210           implementations that support it, this octet string parameter sets
211           the key.
212
213       "maclen" (OSSL_KDF_PARAM_MAC_SIZE) <unsigned integer>
214           Used by implementations that use a MAC with a variable output size
215           (KMAC).  For those KDF implementations that support it, this
216           parameter sets the MAC output size.
217
218           The default value, if any, is implementation dependent.  The length
219           must never exceed what can be given with a size_t.
220
221       "maxmem_bytes" (OSSL_KDF_PARAM_SCRYPT_MAXMEM) <unsigned integer>
222           Memory-hard password-based KDF algorithms, such as scrypt, use an
223           amount of memory that depends on the load factors provided as
224           input.  For those KDF implementations that support it, this
225           uint64_t parameter sets an upper limit on the amount of memory that
226           may be consumed while performing a key derivation.  If this memory
227           usage limit is exceeded because the load factors are chosen too
228           high, the key derivation will fail.
229
230           The default value is implementation dependent.  The memory size
231           must never exceed what can be given with a size_t.
232

RETURN VALUES

234       EVP_KDF_fetch() returns a pointer to a newly fetched EVP_KDF, or NULL
235       if allocation failed.
236
237       EVP_KDF_get0_provider() returns a pointer to the provider for the KDF,
238       or NULL on error.
239
240       EVP_KDF_up_ref() returns 1 on success, 0 on error.
241
242       EVP_KDF_CTX_new() returns either the newly allocated EVP_KDF_CTX
243       structure or NULL if an error occurred.
244
245       EVP_KDF_CTX_free() and EVP_KDF_CTX_reset() do not return a value.
246
247       EVP_KDF_CTX_get_kdf_size() returns the output size.  SIZE_MAX is
248       returned to indicate that the algorithm produces a variable amount of
249       output; 0 to indicate failure.
250
251       EVP_KDF_get0_name() returns the name of the KDF, or NULL on error.
252
253       EVP_KDF_names_do_all() returns 1 if the callback was called for all
254       names. A return value of 0 means that the callback was not called for
255       any names.
256
257       The remaining functions return 1 for success and 0 or a negative value
258       for failure.  In particular, a return value of -2 indicates the
259       operation is not supported by the KDF algorithm.
260

NOTES

262       The KDF life-cycle is described in life_cycle-kdf(7).  In the future,
263       the transitions described there will be enforced.  When this is done,
264       it will not be considered a breaking change to the API.
265

SEE ALSO

267       "Key Derivation Function (KDF)" in OSSL_PROVIDER-default(7),
268       life_cycle-kdf(7).
269

HISTORY

271       This functionality was added to OpenSSL 3.0.
272
274       Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.
275
276       Licensed under the Apache License 2.0 (the "License").  You may not use
277       this file except in compliance with the License.  You can obtain a copy
278       in the file LICENSE in the source distribution or at
279       <https://www.openssl.org/source/license.html>.
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2833.0.5                             2022-11-01                    EVP_KDF(3ossl)
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