xref: /openssl/doc/man3/EVP_KDF.pod (revision 7b08f256) 
1=pod
2
3=head1 NAME
4
5EVP_KDF, EVP_KDF_fetch, EVP_KDF_free, EVP_KDF_up_ref,
6EVP_KDF_CTX, EVP_KDF_CTX_new, EVP_KDF_CTX_free, EVP_KDF_CTX_dup,
7EVP_KDF_CTX_reset, EVP_KDF_derive,
8EVP_KDF_CTX_get_kdf_size,
9EVP_KDF_get0_provider, EVP_KDF_CTX_kdf, EVP_KDF_is_a,
10EVP_KDF_get0_name, EVP_KDF_names_do_all, EVP_KDF_get0_description,
11EVP_KDF_CTX_get_params, EVP_KDF_CTX_set_params, EVP_KDF_do_all_provided,
12EVP_KDF_get_params, EVP_KDF_gettable_params,
13EVP_KDF_gettable_ctx_params, EVP_KDF_settable_ctx_params,
14EVP_KDF_CTX_gettable_params, EVP_KDF_CTX_settable_params - EVP KDF routines
15
16=head1 SYNOPSIS
17
18 #include <openssl/kdf.h>
19
20 typedef struct evp_kdf_st EVP_KDF;
21 typedef struct evp_kdf_ctx_st EVP_KDF_CTX;
22
23 EVP_KDF_CTX *EVP_KDF_CTX_new(EVP_KDF *kdf);
24 const EVP_KDF *EVP_KDF_CTX_kdf(EVP_KDF_CTX *ctx);
25 void EVP_KDF_CTX_free(EVP_KDF_CTX *ctx);
26 EVP_KDF_CTX *EVP_KDF_CTX_dup(const EVP_KDF_CTX *src);
27 void EVP_KDF_CTX_reset(EVP_KDF_CTX *ctx);
28 size_t EVP_KDF_CTX_get_kdf_size(EVP_KDF_CTX *ctx);
29 int EVP_KDF_derive(EVP_KDF_CTX *ctx, unsigned char *key, size_t keylen,
30                    const OSSL_PARAM params[]);
31 int EVP_KDF_up_ref(EVP_KDF *kdf);
32 void EVP_KDF_free(EVP_KDF *kdf);
33 EVP_KDF *EVP_KDF_fetch(OSSL_LIB_CTX *libctx, const char *algorithm,
34                        const char *properties);
35 int EVP_KDF_is_a(const EVP_KDF *kdf, const char *name);
36 const char *EVP_KDF_get0_name(const EVP_KDF *kdf);
37 const char *EVP_KDF_get0_description(const EVP_KDF *kdf);
38 const OSSL_PROVIDER *EVP_KDF_get0_provider(const EVP_KDF *kdf);
39 void EVP_KDF_do_all_provided(OSSL_LIB_CTX *libctx,
40                              void (*fn)(EVP_KDF *kdf, void *arg),
41                              void *arg);
42 int EVP_KDF_names_do_all(const EVP_KDF *kdf,
43                          void (*fn)(const char *name, void *data),
44                          void *data);
45 int EVP_KDF_get_params(EVP_KDF *kdf, OSSL_PARAM params[]);
46 int EVP_KDF_CTX_get_params(EVP_KDF_CTX *ctx, OSSL_PARAM params[]);
47 int EVP_KDF_CTX_set_params(EVP_KDF_CTX *ctx, const OSSL_PARAM params[]);
48 const OSSL_PARAM *EVP_KDF_gettable_params(const EVP_KDF *kdf);
49 const OSSL_PARAM *EVP_KDF_gettable_ctx_params(const EVP_KDF *kdf);
50 const OSSL_PARAM *EVP_KDF_settable_ctx_params(const EVP_KDF *kdf);
51 const OSSL_PARAM *EVP_KDF_CTX_gettable_params(const EVP_KDF *kdf);
52 const OSSL_PARAM *EVP_KDF_CTX_settable_params(const EVP_KDF *kdf);
53 const OSSL_PROVIDER *EVP_KDF_get0_provider(const EVP_KDF *kdf);
54
55=head1 DESCRIPTION
56
57The EVP KDF routines are a high-level interface to Key Derivation Function
58algorithms and should be used instead of algorithm-specific functions.
59
60After creating a B<EVP_KDF_CTX> for the required algorithm using
61EVP_KDF_CTX_new(), inputs to the algorithm are supplied either by
62passing them as part of the EVP_KDF_derive() call or using calls
63to EVP_KDF_CTX_set_params() before calling EVP_KDF_derive() to derive
64the key.
65
66=head2 Types
67
68B<EVP_KDF> is a type that holds the implementation of a KDF.
69
70B<EVP_KDF_CTX> is a context type that holds the algorithm inputs.
71
72=head2 Algorithm implementation fetching
73
74EVP_KDF_fetch() fetches an implementation of a KDF I<algorithm>, given
75a library context I<libctx> and a set of I<properties>.
76See L<crypto(7)/ALGORITHM FETCHING> for further information.
77
78See L<OSSL_PROVIDER-default(7)/Key Derivation Function (KDF)> for the lists of
79algorithms supported by the default provider.
80
81The returned value must eventually be freed with
82L<EVP_KDF_free(3)>.
83
84EVP_KDF_up_ref() increments the reference count of an already fetched
85KDF.
86
87EVP_KDF_free() frees a fetched algorithm.
88NULL is a valid parameter, for which this function is a no-op.
89
90=head2 Context manipulation functions
91
92EVP_KDF_CTX_new() creates a new context for the KDF implementation I<kdf>.
93
94EVP_KDF_CTX_free() frees up the context I<ctx>.  If I<ctx> is NULL, nothing
95is done.
96
97EVP_KDF_CTX_kdf() returns the B<EVP_KDF> associated with the context
98I<ctx>.
99
100=head2 Computing functions
101
102EVP_KDF_CTX_reset() resets the context to the default state as if the context
103had just been created.
104
105EVP_KDF_derive() processes any parameters in I<Params> and then derives
106I<keylen> bytes of key material and places it in the I<key> buffer.
107If the algorithm produces a fixed amount of output then an error will
108occur unless the I<keylen> parameter is equal to that output size,
109as returned by EVP_KDF_CTX_get_kdf_size().
110
111EVP_KDF_get_params() retrieves details about the implementation
112I<kdf>.
113The set of parameters given with I<params> determine exactly what
114parameters should be retrieved.
115Note that a parameter that is unknown in the underlying context is
116simply ignored.
117
118EVP_KDF_CTX_get_params() retrieves chosen parameters, given the
119context I<ctx> and its underlying context.
120The set of parameters given with I<params> determine exactly what
121parameters should be retrieved.
122Note that a parameter that is unknown in the underlying context is
123simply ignored.
124
125EVP_KDF_CTX_set_params() passes chosen parameters to the underlying
126context, given a context I<ctx>.
127The set of parameters given with I<params> determine exactly what
128parameters are passed down.
129Note that a parameter that is unknown in the underlying context is
130simply ignored.
131Also, what happens when a needed parameter isn't passed down is
132defined by the implementation.
133
134EVP_KDF_gettable_params() returns an L<OSSL_PARAM(3)> array that describes
135the retrievable and settable parameters.  EVP_KDF_gettable_params()
136returns parameters that can be used with EVP_KDF_get_params().
137
138EVP_KDF_gettable_ctx_params() and EVP_KDF_CTX_gettable_params()
139return constant L<OSSL_PARAM(3)> arrays that describe the retrievable
140parameters that can be used with EVP_KDF_CTX_get_params().
141EVP_KDF_gettable_ctx_params() returns the parameters that can be retrieved
142from the algorithm, whereas EVP_KDF_CTX_gettable_params() returns
143the parameters that can be retrieved in the context's current state.
144
145EVP_KDF_settable_ctx_params() and EVP_KDF_CTX_settable_params() return
146constant L<OSSL_PARAM(3)> arrays that describe the settable parameters that
147can be used with EVP_KDF_CTX_set_params().  EVP_KDF_settable_ctx_params()
148returns the parameters that can be retrieved from the algorithm,
149whereas EVP_KDF_CTX_settable_params() returns the parameters that can
150be retrieved in the context's current state.
151
152=head2 Information functions
153
154EVP_KDF_CTX_get_kdf_size() returns the output size if the algorithm produces a fixed amount
155of output and B<SIZE_MAX> otherwise.  If an error occurs then 0 is returned.
156For some algorithms an error may result if input parameters necessary to
157calculate a fixed output size have not yet been supplied.
158
159EVP_KDF_is_a() returns 1 if I<kdf> is an implementation of an
160algorithm that's identifiable with I<name>, otherwise 0.
161
162EVP_KDF_get0_provider() returns the provider that holds the implementation
163of the given I<kdf>.
164
165EVP_KDF_do_all_provided() traverses all KDF implemented by all activated
166providers in the given library context I<libctx>, and for each of the
167implementations, calls the given function I<fn> with the implementation method
168and the given I<arg> as argument.
169
170EVP_KDF_get0_name() return the name of the given KDF.  For fetched KDFs
171with multiple names, only one of them is returned; it's
172recommended to use EVP_KDF_names_do_all() instead.
173
174EVP_KDF_names_do_all() traverses all names for I<kdf>, and calls
175I<fn> with each name and I<data>.
176
177EVP_KDF_get0_description() returns a description of the I<kdf>, meant for
178display and human consumption.  The description is at the discretion of
179the I<kdf> implementation.
180
181=head1 PARAMETERS
182
183The standard parameter names are:
184
185=over 4
186
187=item "pass" (B<OSSL_KDF_PARAM_PASSWORD>) <octet string>
188
189Some KDF implementations require a password.
190For those KDF implementations that support it, this parameter sets the password.
191
192=item "salt" (B<OSSL_KDF_PARAM_SALT>) <octet string>
193
194Some KDF implementations can take a non-secret unique cryptographic salt.
195For those KDF implementations that support it, this parameter sets the salt.
196
197The default value, if any, is implementation dependent.
198
199=item "iter" (B<OSSL_KDF_PARAM_ITER>) <unsigned integer>
200
201Some KDF implementations require an iteration count.
202For those KDF implementations that support it, this parameter sets the
203iteration count.
204
205The default value, if any, is implementation dependent.
206
207=item "properties" (B<OSSL_KDF_PARAM_PROPERTIES>) <UTF8 string>
208
209=item "mac" (B<OSSL_KDF_PARAM_MAC>) <UTF8 string>
210
211=item "digest" (B<OSSL_KDF_PARAM_DIGEST>) <UTF8 string>
212
213=item "cipher" (B<OSSL_KDF_PARAM_CIPHER>) <UTF8 string>
214
215For KDF implementations that use an underlying computation MAC, digest or
216cipher, these parameters set what the algorithm should be.
217
218The value is always the name of the intended algorithm,
219or the properties.
220
221Note that not all algorithms may support all possible underlying
222implementations.
223
224=item "key" (B<OSSL_KDF_PARAM_KEY>) <octet string>
225
226Some KDF implementations require a key.
227For those KDF implementations that support it, this octet string parameter
228sets the key.
229
230=item "info" (B<OSSL_KDF_PARAM_INFO>) <octet string>
231
232Some KDF implementations, such as L<EVP_KDF-HKDF(7)>, take an 'info' parameter
233for binding the derived key material
234to application- and context-specific information.
235This parameter sets the info, fixed info, other info or shared info argument.
236You can specify this parameter multiple times, and each instance will
237be concatenated to form the final value.
238
239=item "maclen" (B<OSSL_KDF_PARAM_MAC_SIZE>) <unsigned integer>
240
241Used by implementations that use a MAC with a variable output size (KMAC).
242For those KDF implementations that support it, this parameter
243sets the MAC output size.
244
245The default value, if any, is implementation dependent.
246The length must never exceed what can be given with a B<size_t>.
247
248=item "maxmem_bytes" (B<OSSL_KDF_PARAM_SCRYPT_MAXMEM>) <unsigned integer>
249
250Memory-hard password-based KDF algorithms, such as scrypt, use an amount of
251memory that depends on the load factors provided as input.
252For those KDF implementations that support it, this B<uint64_t> parameter sets
253an upper limit on the amount of memory that may be consumed while performing
254a key derivation.
255If this memory usage limit is exceeded because the load factors are chosen
256too high, the key derivation will fail.
257
258The default value is implementation dependent.
259The memory size must never exceed what can be given with a B<size_t>.
260
261=back
262
263=head1 RETURN VALUES
264
265EVP_KDF_fetch() returns a pointer to a newly fetched B<EVP_KDF>, or
266NULL if allocation failed.
267
268EVP_KDF_get0_provider() returns a pointer to the provider for the KDF, or
269NULL on error.
270
271EVP_KDF_up_ref() returns 1 on success, 0 on error.
272
273EVP_KDF_CTX_new() returns either the newly allocated
274B<EVP_KDF_CTX> structure or NULL if an error occurred.
275
276EVP_KDF_CTX_free() and EVP_KDF_CTX_reset() do not return a value.
277
278EVP_KDF_CTX_get_kdf_size() returns the output size.  B<SIZE_MAX> is returned to indicate
279that the algorithm produces a variable amount of output; 0 to indicate failure.
280
281EVP_KDF_get0_name() returns the name of the KDF, or NULL on error.
282
283EVP_KDF_names_do_all() returns 1 if the callback was called for all names. A
284return value of 0 means that the callback was not called for any names.
285
286The remaining functions return 1 for success and 0 for failure.
287
288=head1 NOTES
289
290The KDF life-cycle is described in L<life_cycle-kdf(7)>.  In the future,
291the transitions described there will be enforced.  When this is done, it will
292not be considered a breaking change to the API.
293
294=head1 SEE ALSO
295
296L<OSSL_PROVIDER-default(7)/Key Derivation Function (KDF)>,
297L<life_cycle-kdf(7)>.
298
299=head1 HISTORY
300
301This functionality was added in OpenSSL 3.0.
302
303=head1 COPYRIGHT
304
305Copyright 2019-2024 The OpenSSL Project Authors. All Rights Reserved.
306
307Licensed under the Apache License 2.0 (the "License").  You may not use
308this file except in compliance with the License.  You can obtain a copy
309in the file LICENSE in the source distribution or at
310L<https://www.openssl.org/source/license.html>.
311
312=cut
313