5 OSSL_PARAM - a structure to pass or request object parameters
9 #include <openssl/core.h>
11 typedef struct ossl_param_st OSSL_PARAM;
12 struct ossl_param_st {
13 const char *key; /* the name of the parameter */
14 unsigned char data_type; /* declare what kind of content is in data */
15 void *data; /* value being passed in or out */
16 size_t data_size; /* data size */
17 size_t return_size; /* returned size */
22 B<OSSL_PARAM> is a type that allows passing arbitrary data for some
23 object between two parties that have no or very little shared
24 knowledge about their respective internal structures for that object.
26 A typical usage example could be an application that wants to set some
27 parameters for an object, or wants to find out some parameters of an
30 Arrays of this type can be used for the following purposes:
34 =item * Setting parameters for some object
36 The caller sets up the B<OSSL_PARAM> array and calls some function
37 (the I<setter>) that has intimate knowledge about the object that can
38 take the data from the B<OSSL_PARAM> array and assign them in a
39 suitable form for the internal structure of the object.
41 =item * Request parameters of some object
43 The caller (the I<requestor>) sets up the B<OSSL_PARAM> array and
44 calls some function (the I<responder>) that has intimate knowledge
45 about the object, which can take the internal data of the object and
46 copy (possibly convert) that to the memory prepared by the
47 I<requestor> and pointed at with the B<OSSL_PARAM> I<data>.
49 =item * Request parameter descriptors
51 The caller gets an array of constant B<OSSL_PARAM>, which describe
52 available parameters and some of their properties; name, data type and
54 For a detailed description of each field for this use, see the field
57 The caller may then use the information from this descriptor array to
58 build up its own B<OSSL_PARAM> array to pass down to a I<setter> or
63 Normally, the order of the an B<OSSL_PARAM> array is not relevant.
64 However, if the I<responder> can handle multiple elements with the
65 same key, those elements must be handled in the order they are in.
67 =head2 B<OSSL_PARAM> fields
73 The identity of the parameter in the form of a string.
77 The I<data_type> is a value that describes the type and organization of
79 See L</Supported types> below for a description of the types.
85 I<data> is a pointer to the memory where the parameter data is (when
86 setting parameters) or shall (when requesting parameters) be stored,
87 and I<data_size> is its size in bytes.
88 The organization of the data depends on the parameter type and flag.
90 When the B<OSSL_PARAM> is used as a parameter descriptor, I<data>
92 If I<data_size> is zero, it means that an arbitrary data size is
93 accepted, otherwise it specifies the maximum size allowed.
97 When an array of B<OSSL_PARAM> is used to request data, the
98 I<responder> must set this field to indicate the actual size of the
100 In case the I<data_size> is too small for the data, the I<responder>
101 must still set this field to indicate the minimum data size required.
103 When the B<OSSL_PARAM> is used as a parameter descriptor,
104 I<return_size> should be ignored.
110 The key names and associated types are defined by the entity that
111 offers these parameters, i.e. names for parameters provided by the
112 OpenSSL libraries are defined by the libraries, and names for
113 parameters provided by providers are defined by those providers,
114 except for the pointer form of strings (see data type descriptions
116 Entities that want to set or request parameters need to know what
117 those keys are and of what type, any functionality between those two
118 entities should remain oblivious and just pass the B<OSSL_PARAM> array
121 =head2 Supported types
123 The I<data_type> field can be one of the following types:
127 =item B<OSSL_PARAM_INTEGER>
129 =item B<OSSL_PARAM_UNSIGNED_INTEGER>
131 The parameter data is an integer (signed or unsigned) of arbitrary
132 length, organized in native form, i.e. most significant byte first on
133 Big-Endian systems, and least significant byte first on Little-Endian
136 =item B<OSSL_PARAM_REAL>
138 The parameter data is a floating point value in native form.
140 =item B<OSSL_PARAM_UTF8_STRING>
142 The parameter data is a printable string.
144 =item B<OSSL_PARAM_OCTET_STRING>
146 The parameter data is an arbitrary string of bytes.
148 =item B<OSSL_PARAM_UTF8_PTR>
150 The parameter data is a pointer to a printable string.
152 The difference between this and B<OSSL_PARAM_UTF8_STRING> is that I<data>
153 doesn't point directly at the data, but to a pointer that points to the data.
155 This is used to indicate that constant data is or will be passed,
156 and there is therefore no need to copy the data that is passed, just
159 I<data_size> must be set to the size of the data, not the size of the
161 If this is used in a parameter request,
162 I<data_size> is not relevant. However, the I<responder> will set
163 I<return_size> to the size of the data.
165 Note that the use of this type is B<fragile> and can only be safely
166 used for data that remains constant and in a constant location for a
167 long enough duration (such as the life-time of the entity that
168 offers these parameters).
170 =item B<OSSL_PARAM_OCTET_PTR>
172 The parameter data is a pointer to an arbitrary string of bytes.
174 The difference between this and B<OSSL_PARAM_OCTET_STRING> is that
175 I<data> doesn't point directly at the data, but to a pointer that
178 This is used to indicate that constant data is or will be passed, and
179 there is therefore no need to copy the data that is passed, just the
182 I<data_size> must be set to the size of the data, not the size of the
184 If this is used in a parameter request,
185 I<data_size> is not relevant. However, the I<responder> will set
186 I<return_size> to the size of the data.
188 Note that the use of this type is B<fragile> and can only be safely
189 used for data that remains constant and in a constant location for a
190 long enough duration (such as the life-time of the entity that
191 offers these parameters).
197 Both when setting and requesting parameters, the functions that are
198 called will have to decide what is and what is not an error.
199 The recommended behaviour is:
205 Keys that a I<setter> or I<responder> doesn't recognise should simply
207 That in itself isn't an error.
211 If the keys that a called I<setter> recognises form a consistent
212 enough set of data, that call should succeed.
216 Apart from the I<return_size>, a I<responder> must never change the fields
218 To return a value, it should change the contents of the memory that
223 If the data type for a key that it's associated with is incorrect,
224 the called function may return an error.
226 The called function may also try to convert the data to a suitable
227 form (for example, it's plausible to pass a large number as an octet
228 string, so even though a given key is defined as an
229 B<OSSL_PARAM_UNSIGNED_INTEGER>, is plausible to pass the value as an
230 B<OSSL_PARAM_OCTET_STRING>), but this is in no way mandatory.
234 If a I<responder> finds that some data sizes are too small for the
235 requested data, it must set I<return_size> for each such
236 B<OSSL_PARAM> item to the required size, and eventually return an
241 =begin comment RETURN VALUES doesn't make sense for a manual that only
242 describes a type, but document checkers still want that section, and
243 to have more than just the section title.
253 A couple of examples to just show how B<OSSL_PARAM> arrays could be
258 This example is for setting parameters on some object:
260 #include <openssl/core.h>
262 const char *foo = "some string";
263 size_t foo_l = strlen(foo) + 1;
264 const char bar[] = "some other string";
266 { "foo", OSSL_PARAM_UTF8_STRING_PTR, &foo, foo_l, 0 },
267 { "bar", OSSL_PARAM_UTF8_STRING, &bar, sizeof(bar), 0 },
268 { NULL, 0, NULL, 0, NULL }
273 This example is for requesting parameters on some object:
275 const char *foo = NULL;
279 OSSL_PARAM request[] = {
280 { "foo", OSSL_PARAM_UTF8_STRING_PTR, &foo, 0 /*irrelevant*/, 0 },
281 { "bar", OSSL_PARAM_UTF8_STRING, &bar, sizeof(bar), 0 },
282 { NULL, 0, NULL, 0, NULL }
285 A I<responder> that receives this array (as I<params> in this example)
286 could fill in the parameters like this:
288 /* OSSL_PARAM *params */
292 for (i = 0; params[i].key != NULL; i++) {
293 if (strcmp(params[i].key, "foo") == 0) {
294 *(char **)params[i].data = "foo value";
295 params[i].return_size = 10; /* size of "foo value" */
296 } else if (strcmp(params[i].key, "bar") == 0) {
297 memcpy(params[i].data, "bar value", 10);
298 params[i].return_size = 10; /* size of "bar value" */
300 /* Ignore stuff we don't know */
305 L<openssl-core.h(7)>, L<OSSL_PARAM_get_int(3)>
309 B<OSSL_PARAM> was added in OpenSSL 3.0.
313 Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
315 Licensed under the Apache License 2.0 (the "License"). You may not use
316 this file except in compliance with the License. You can obtain a copy
317 in the file LICENSE in the source distribution or at
318 L<https://www.openssl.org/source/license.html>.