178 lines
6.2 KiB
Plaintext
178 lines
6.2 KiB
Plaintext
=pod
|
|
|
|
=head1 NAME
|
|
|
|
property - Properties, a selection mechanism for algorithm implementations
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
As of OpenSSL 3.0, a new method has been introduced to decide which of
|
|
multiple implementations of an algorithm will be used.
|
|
The method is centered around the concept of properties.
|
|
Each implementation defines a number of properties and when an algorithm
|
|
is being selected, filters based on these properties can be used to
|
|
choose the most appropriate implementation of the algorithm.
|
|
|
|
Properties are like variables, they are referenced by name and have a value
|
|
assigned.
|
|
|
|
=head2 Property Names
|
|
|
|
Property names fall into two categories: those reserved by the OpenSSL
|
|
project and user defined names.
|
|
A I<reserved> property name consists of a single C-style identifier
|
|
(except for leading underscores not being permitted), which begins
|
|
with a letter and can be followed by any number of letters, numbers
|
|
and underscores.
|
|
Property names are case-insensitive, but OpenSSL will only use lowercase
|
|
letters.
|
|
|
|
A I<user defined> property name is similar, but it B<must> consist of
|
|
two or more C-style identifiers, separated by periods.
|
|
The last identifier in the name can be considered the 'true' property
|
|
name, which is prefixed by some sort of 'namespace'.
|
|
Providers for example could include their name in the prefix and use
|
|
property names like
|
|
|
|
<provider_name>.<property_name>
|
|
<provider_name>.<algorithm_name>.<property_name>
|
|
|
|
=head2 Properties
|
|
|
|
A I<property> is a I<name=value> pair.
|
|
A I<property definition> is a sequence of comma separated properties.
|
|
There can be any number of properties in a definition, however each name must
|
|
be unique.
|
|
For example: "" defines an empty property definition (i.e., no restriction);
|
|
"my.foo=bar" defines a property named I<my.foo> which has a string value I<bar>
|
|
and "iteration.count=3" defines a property named I<iteration.count> which
|
|
has a numeric value of I<3>.
|
|
The full syntax for property definitions appears below.
|
|
|
|
=head2 Implementations
|
|
|
|
Each implementation of an algorithm can define any number of
|
|
properties.
|
|
For example, the default provider defines the property I<provider=default>
|
|
for all of its algorithms.
|
|
Likewise, OpenSSL's FIPS provider defines I<provider=fips> and the legacy
|
|
provider defines I<provider=legacy> for all of their algorithms.
|
|
|
|
=head2 Queries
|
|
|
|
A I<property query clause> is a single conditional test.
|
|
For example, "fips=yes", "provider!=default" or "?iteration.count=3".
|
|
The first two represent mandatory clauses, such clauses B<must> match
|
|
for any algorithm to even be under consideration.
|
|
The third clause represents an optional clause.
|
|
Matching such clauses is not a requirement, but any additional optional
|
|
match counts in favor of the algorithm.
|
|
More details about that in the B<Lookups> section.
|
|
A I<property query> is a sequence of comma separated property query clauses.
|
|
It is an error if a property name appears in more than one query clause.
|
|
The full syntax for property queries appears below, but the available syntactic
|
|
features are:
|
|
|
|
=over 4
|
|
|
|
=item *
|
|
|
|
B<=> is an infix operator providing an equality test.
|
|
|
|
=item *
|
|
|
|
B<!=> is an infix operator providing an inequality test.
|
|
|
|
=item *
|
|
|
|
B<?> is a prefix operator that means that the following clause is optional
|
|
but preferred.
|
|
|
|
=item *
|
|
|
|
B<-> is a prefix operator that means any global query clause involving the
|
|
following property name should be ignored.
|
|
|
|
=item *
|
|
|
|
B<"..."> is a quoted string.
|
|
The quotes are not included in the body of the string.
|
|
|
|
=item *
|
|
|
|
B<'...'> is a quoted string.
|
|
The quotes are not included in the body of the string.
|
|
|
|
=back
|
|
|
|
=head2 Lookups
|
|
|
|
When an algorithm is looked up, a property query is used to determine
|
|
the best matching algorithm.
|
|
All mandatory query clauses B<must> be present and the implementation
|
|
that additionally has the largest number of matching optional query
|
|
clauses will be used.
|
|
If there is more than one such optimal candidate, the result will be
|
|
chosen from amongst those in an indeterminate way.
|
|
Ordering of optional clauses is not significant.
|
|
|
|
=head2 Shortcut
|
|
|
|
In order to permit a more concise expression of boolean properties, there
|
|
is one short cut: a property name alone (e.g. "my.property") is
|
|
exactly equivalent to "my.property=yes" in both definitions and queries.
|
|
|
|
=head2 Global and Local
|
|
|
|
Two levels of property query are supported.
|
|
A context based property query that applies to all fetch operations and a local
|
|
property query.
|
|
Where both the context and local queries include a clause with the same name,
|
|
the local clause overrides the context clause.
|
|
|
|
It is possible for a local property query to remove a clause in the context
|
|
property query by preceding the property name with a '-'.
|
|
For example, a context property query that contains "fips=yes" would normally
|
|
result in implementations that have "fips=yes".
|
|
|
|
However, if the setting of the "fips" property is irrelevant to the
|
|
operations being performed, the local property query can include the
|
|
clause "-fips".
|
|
Note that the local property query could not use "fips=no" because that would
|
|
disallow any implementations with "fips=yes" rather than not caring about the
|
|
setting.
|
|
|
|
=head1 SYNTAX
|
|
|
|
The lexical syntax in EBNF is given by:
|
|
|
|
Definition ::= PropertyName ( '=' Value )?
|
|
( ',' PropertyName ( '=' Value )? )*
|
|
Query ::= PropertyQuery ( ',' PropertyQuery )*
|
|
PropertyQuery ::= '-' PropertyName
|
|
| '?'? ( PropertyName (( '=' | '!=' ) Value)?)
|
|
Value ::= NumberLiteral | StringLiteral
|
|
StringLiteral ::= QuotedString | UnquotedString
|
|
QuotedString ::= '"' [^"]* '"' | "'" [^']* "'"
|
|
UnquotedString ::= [A-Za-z] [^{space},]+
|
|
NumberLiteral ::= '0' ( [0-7]* | 'x' [0-9A-Fa-f]+ ) | '-'? [1-9] [0-9]+
|
|
PropertyName ::= [A-Za-z] [A-Za-z0-9_]* ( '.' [A-Za-z] [A-Za-z0-9_]* )*
|
|
|
|
The flavour of EBNF being used is defined by:
|
|
L<https://www.w3.org/TR/2010/REC-xquery-20101214/#EBNFNotation>.
|
|
|
|
=head1 HISTORY
|
|
|
|
Properties were added in OpenSSL 3.0
|
|
|
|
=head1 COPYRIGHT
|
|
|
|
Copyright 2019-2023 The OpenSSL Project Authors. All Rights Reserved.
|
|
|
|
Licensed under the Apache License 2.0 (the "License"). You may not use
|
|
this file except in compliance with the License. You can obtain a copy
|
|
in the file LICENSE in the source distribution or at
|
|
L<https://www.openssl.org/source/license.html>.
|
|
|
|
=cut
|