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 I<requesting parameters>, it's acceptable for I<data> to be NULL.
91 This can be used by the I<requestor> to figure out dynamically exactly
92 how much buffer space is needed to store the parameter data.
93 In this case, I<data_size> is ignored.
95 When the B<OSSL_PARAM> is used as a parameter descriptor, I<data>
97 If I<data_size> is zero, it means that an arbitrary data size is
98 accepted, otherwise it specifies the maximum size allowed.
102 When an array of B<OSSL_PARAM> is used to request data, the
103 I<responder> must set this field to indicate the actual size of the
105 In case the I<data_size> is too small for the data, the I<responder>
106 must still set this field to indicate the minimum data size required.
108 When the B<OSSL_PARAM> is used as a parameter descriptor,
109 I<return_size> should be ignored.
115 The key names and associated types are defined by the entity that
116 offers these parameters, i.e. names for parameters provided by the
117 OpenSSL libraries are defined by the libraries, and names for
118 parameters provided by providers are defined by those providers,
119 except for the pointer form of strings (see data type descriptions
121 Entities that want to set or request parameters need to know what
122 those keys are and of what type, any functionality between those two
123 entities should remain oblivious and just pass the B<OSSL_PARAM> array
126 =head2 Supported types
128 The I<data_type> field can be one of the following types:
132 =item B<OSSL_PARAM_INTEGER>
134 =item B<OSSL_PARAM_UNSIGNED_INTEGER>
136 The parameter data is an integer (signed or unsigned) of arbitrary
137 length, organized in native form, i.e. most significant byte first on
138 Big-Endian systems, and least significant byte first on Little-Endian
141 =item B<OSSL_PARAM_REAL>
143 The parameter data is a floating point value in native form.
145 =item B<OSSL_PARAM_UTF8_STRING>
147 The parameter data is a printable string.
149 =item B<OSSL_PARAM_OCTET_STRING>
151 The parameter data is an arbitrary string of bytes.
153 =item B<OSSL_PARAM_UTF8_PTR>
155 The parameter data is a pointer to a printable string.
157 The difference between this and B<OSSL_PARAM_UTF8_STRING> is that I<data>
158 doesn't point directly at the data, but to a pointer that points to the data.
160 This is used to indicate that constant data is or will be passed,
161 and there is therefore no need to copy the data that is passed, just
164 I<data_size> must be set to the size of the data, not the size of the
166 If this is used in a parameter request,
167 I<data_size> is not relevant. However, the I<responder> will set
168 I<return_size> to the size of the data.
170 Note that the use of this type is B<fragile> and can only be safely
171 used for data that remains constant and in a constant location for a
172 long enough duration (such as the life-time of the entity that
173 offers these parameters).
175 =item B<OSSL_PARAM_OCTET_PTR>
177 The parameter data is a pointer to an arbitrary string of bytes.
179 The difference between this and B<OSSL_PARAM_OCTET_STRING> is that
180 I<data> doesn't point directly at the data, but to a pointer that
183 This is used to indicate that constant data is or will be passed, and
184 there is therefore no need to copy the data that is passed, just the
187 I<data_size> must be set to the size of the data, not the size of the
189 If this is used in a parameter request,
190 I<data_size> is not relevant. However, the I<responder> will set
191 I<return_size> to the size of the data.
193 Note that the use of this type is B<fragile> and can only be safely
194 used for data that remains constant and in a constant location for a
195 long enough duration (such as the life-time of the entity that
196 offers these parameters).
202 Both when setting and requesting parameters, the functions that are
203 called will have to decide what is and what is not an error.
204 The recommended behaviour is:
210 Keys that a I<setter> or I<responder> doesn't recognise should simply
212 That in itself isn't an error.
216 If the keys that a called I<setter> recognises form a consistent
217 enough set of data, that call should succeed.
221 Apart from the I<return_size>, a I<responder> must never change the fields
223 To return a value, it should change the contents of the memory that
228 If the data type for a key that it's associated with is incorrect,
229 the called function may return an error.
231 The called function may also try to convert the data to a suitable
232 form (for example, it's plausible to pass a large number as an octet
233 string, so even though a given key is defined as an
234 B<OSSL_PARAM_UNSIGNED_INTEGER>, is plausible to pass the value as an
235 B<OSSL_PARAM_OCTET_STRING>), but this is in no way mandatory.
239 If a I<responder> finds that some data sizes are too small for the
240 requested data, it must set I<return_size> for each such
241 B<OSSL_PARAM> item to the required size, and eventually return an
246 =begin comment RETURN VALUES doesn't make sense for a manual that only
247 describes a type, but document checkers still want that section, and
248 to have more than just the section title.
258 A couple of examples to just show how B<OSSL_PARAM> arrays could be
263 This example is for setting parameters on some object:
265 #include <openssl/core.h>
267 const char *foo = "some string";
268 size_t foo_l = strlen(foo) + 1;
269 const char bar[] = "some other string";
271 { "foo", OSSL_PARAM_UTF8_STRING_PTR, &foo, foo_l, 0 },
272 { "bar", OSSL_PARAM_UTF8_STRING, &bar, sizeof(bar), 0 },
273 { NULL, 0, NULL, 0, NULL }
278 This example is for requesting parameters on some object:
280 const char *foo = NULL;
284 OSSL_PARAM request[] = {
285 { "foo", OSSL_PARAM_UTF8_STRING_PTR, &foo, 0 /*irrelevant*/, 0 },
286 { "bar", OSSL_PARAM_UTF8_STRING, &bar, sizeof(bar), 0 },
287 { NULL, 0, NULL, 0, NULL }
290 A I<responder> that receives this array (as I<params> in this example)
291 could fill in the parameters like this:
293 /* OSSL_PARAM *params */
297 for (i = 0; params[i].key != NULL; i++) {
298 if (strcmp(params[i].key, "foo") == 0) {
299 *(char **)params[i].data = "foo value";
300 params[i].return_size = 10; /* size of "foo value" */
301 } else if (strcmp(params[i].key, "bar") == 0) {
302 memcpy(params[i].data, "bar value", 10);
303 params[i].return_size = 10; /* size of "bar value" */
305 /* Ignore stuff we don't know */
310 L<openssl-core.h(7)>, L<OSSL_PARAM_get_int(3)>
314 B<OSSL_PARAM> was added in OpenSSL 3.0.
318 Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
320 Licensed under the Apache License 2.0 (the "License"). You may not use
321 this file except in compliance with the License. You can obtain a copy
322 in the file LICENSE in the source distribution or at
323 L<https://www.openssl.org/source/license.html>.