{
    "mode": "man",
    "parameter": "property",
    "section": "7",
    "url": "https://www.chedong.com/phpMan.php/man/property/7/json",
    "generated": "2026-06-03T01:22:36Z",
    "sections": {
        "NAME": {
            "content": "property - Properties, a selection mechanism for algorithm implementations\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "As of OpenSSL 3.0, a new method has been introduced to decide which of multiple\nimplementations of an algorithm will be used.  The method is centered around the concept of\nproperties.  Each implementation defines a number of properties and when an algorithm is\nbeing selected, filters based on these properties can be used to choose the most appropriate\nimplementation of the algorithm.\n\nProperties are like variables, they are referenced by name and have a value assigned.\n",
            "subsections": [
                {
                    "name": "Property Names",
                    "content": "Property names fall into two categories: those reserved by the OpenSSL project and user\ndefined names.  A reserved property name consists of a single C-style identifier (except for\nleading underscores not being permitted), which begins with a letter and can be followed by\nany number of letters, numbers and underscores.  Property names are case-insensitive, but\nOpenSSL will only use lowercase letters.\n\nA user defined property name is similar, but it must consist of two or more C-style\nidentifiers, separated by periods.  The last identifier in the name can be considered the\n'true' property name, which is prefixed by some sort of 'namespace'.  Providers for example\ncould include their name in the prefix and use property names like\n\n<providername>.<propertyname>\n<providername>.<algorithmname>.<propertyname>\n"
                },
                {
                    "name": "Properties",
                    "content": "A property is a name=value pair.  A property definition is a sequence of comma separated\nproperties.  There can be any number of properties in a definition, however each name must be\nunique.  For example: \"\" defines an empty property definition (i.e., no restriction);\n\"my.foo=bar\" defines a property named my.foo which has a string value bar and\n\"iteration.count=3\" defines a property named iteration.count which has a numeric value of 3.\nThe full syntax for property definitions appears below.\n"
                },
                {
                    "name": "Implementations",
                    "content": "Each implementation of an algorithm can define any number of properties.  For example, the\ndefault provider defines the property provider=default for all of its algorithms.  Likewise,\nOpenSSL's FIPS provider defines provider=fips and the legacy provider defines provider=legacy\nfor all of their algorithms.\n"
                },
                {
                    "name": "Queries",
                    "content": "A property query clause is a single conditional test.  For example, \"fips=yes\",\n\"provider!=default\" or \"?iteration.count=3\".  The first two represent mandatory clauses, such\nclauses must match for any algorithm to even be under consideration.  The third clause\nrepresents an optional clause.  Matching such clauses is not a requirement, but any\nadditional optional match counts in favor of the algorithm.  More details about that in the\nLookups section.  A property query is a sequence of comma separated property query clauses.\nIt is an error if a property name appears in more than one query clause.  The full syntax for\nproperty queries appears below, but the available syntactic features are:\n\n•   = is an infix operator providing an equality test.\n\n•   != is an infix operator providing an inequality test.\n\n•   ? is a prefix operator that means that the following clause is optional but preferred.\n\n•   - is a prefix operator that means any global query clause involving the following\nproperty name should be ignored.\n\n•   \"...\" is a quoted string.  The quotes are not included in the body of the string.\n\n•   '...' is a quoted string.  The quotes are not included in the body of the string.\n"
                },
                {
                    "name": "Lookups",
                    "content": "When an algorithm is looked up, a property query is used to determine the best matching\nalgorithm.  All mandatory query clauses must be present and the implementation that\nadditionally has the largest number of matching optional query clauses will be used.  If\nthere is more than one such optimal candidate, the result will be chosen from amongst those\nin an indeterminate way.  Ordering of optional clauses is not significant.\n"
                },
                {
                    "name": "Shortcut",
                    "content": "In order to permit a more concise expression of boolean properties, there is one short cut: a\nproperty name alone (e.g. \"my.property\") is exactly equivalent to \"my.property=yes\" in both\ndefinitions and queries.\n"
                },
                {
                    "name": "Global and Local",
                    "content": "Two levels of property query are supported.  A context based property query that applies to\nall fetch operations and a local property query.  Where both the context and local queries\ninclude a clause with the same name, the local clause overrides the context clause.\n\nIt is possible for a local property query to remove a clause in the context property query by\npreceding the property name with a '-'.  For example, a context property query that contains\n\"fips=yes\" would normally result in implementations that have \"fips=yes\".\n\nHowever, if the setting of the \"fips\" property is irrelevant to the operations being\nperformed, the local property query can include the clause \"-fips\".  Note that the local\nproperty query could not use \"fips=no\" because that would disallow any implementations with\n\"fips=yes\" rather than not caring about the setting.\n"
                }
            ]
        },
        "SYNTAX": {
            "content": "The lexical syntax in EBNF is given by:\n\nDefinition     ::= PropertyName ( '=' Value )?\n( ',' PropertyName ( '=' Value )? )*\nQuery          ::= PropertyQuery ( ',' PropertyQuery )*\nPropertyQuery  ::= '-' PropertyName\n| '?'? ( PropertyName (( '=' | '!=' ) Value)?)\nValue          ::= NumberLiteral | StringLiteral\nStringLiteral  ::= QuotedString | UnquotedString\nQuotedString   ::= '\"' [^\"]* '\"' | \"'\" [^']* \"'\"\nUnquotedString ::= [^{space},]+\nNumberLiteral  ::= '0' ( [0-7]* | 'x' [0-9A-Fa-f]+ ) | '-'? [1-9] [0-9]+\nPropertyName   ::= [A-Z] [A-Z0-9]* ( '.' [A-Z] [A-Z0-9]* )*\n",
            "subsections": []
        },
        "HISTORY": {
            "content": "Properties were added in OpenSSL 3.0\n",
            "subsections": []
        },
        "COPYRIGHT": {
            "content": "Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.\n\nLicensed under the Apache License 2.0 (the \"License\").  You may not use this file except in\ncompliance with the License.  You can obtain a copy in the file LICENSE in the source\ndistribution or at <https://www.openssl.org/source/license.html>.\n\n\n\n3.0.2                                        2026-04-07                               PROPERTY(7SSL)",
            "subsections": []
        }
    },
    "summary": "property - Properties, a selection mechanism for algorithm implementations",
    "flags": [],
    "examples": [],
    "see_also": []
}