276 lines
10 KiB
Groff
Executable File
276 lines
10 KiB
Groff
Executable File
.\" Automatically generated by Pod::Man 2.25 (Pod::Simple 3.16)
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.\" ========================================================================
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.\"
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.IX Title "PROPERTY 7"
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.TH PROPERTY 7 "2020-03-02" "3.0.0-dev" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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property \- Properties, a selection mechanism for algorithm implementations
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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As of OpenSSL 3.0, a new method has been introduced to decide which of
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multiple implementations of an algorithm will be used.
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The method is centered around the concept of properties.
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Each implementation defines a number of properties and when an algorithm
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is being selected, filters based on these properties can be used to
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choose the most appropriate implementation of the algorithm.
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.PP
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Properties are like variables, they are referenced by name and have a value
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assigned.
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.SS "Property Names"
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.IX Subsection "Property Names"
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Property names fall into two categories: those reserved by the OpenSSL
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project and user defined names.
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A \fIreserved\fR property name consists of a single C\-style identifier
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(except for leading underscores not being permitted), which begins
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with a letter and can be followed by any number of letters, numbers
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and underscores.
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Property names are case-insensitive, but OpenSSL will only use lowercase
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letters.
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.PP
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A \fIuser defined\fR property name is similar, but it \fBmust\fR consist of
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two or more C\-style identifiers, separated by periods.
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The last identifier in the name can be considered the 'true' property
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name, which is prefixed by some sort of 'namespace'.
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Providers for example could include their name in the prefix and use
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property names like
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.PP
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.Vb 2
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\& <provider_name>.<property_name>
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\& <provider_name>.<algorithm_name>.<property_name>
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.Ve
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.SS "Properties"
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.IX Subsection "Properties"
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A \fIproperty\fR is a \fIname=value\fR pair.
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A \fIproperty definition\fR is a sequence of comma separated properties.
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There can be any number of properties in a definition.
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For example: "\*(L" defines a null property definition; \*(R"my.foo=bar"
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defines a property named \fImy.foo\fR which has a string value \fIbar\fR and
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\&\*(L"iteration.count=3\*(R" defines a property named \fIiteration.count\fR which
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has a numeric value of \fI3\fR.
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The full syntax for property definitions appears below.
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.SS "Implementations"
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.IX Subsection "Implementations"
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Each implementation of an algorithm can define any number of
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properties.
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For example, the default provider defines the property \fIprovider=default\fR
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for all of its algorithms.
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Likewise, OpenSSL's \s-1FIPS\s0 provider defines \fIprovider=fips\fR and the legacy
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provider defines \fIprovider=legacy\fR for all of their algorithms.
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.SS "Queries"
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.IX Subsection "Queries"
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A \fIproperty query clause\fR is a single conditional test.
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For example, \*(L"fips=yes\*(R", \*(L"provider!=default\*(R" or \*(L"?iteration.count!=3\*(R".
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The first two represent mandatory clauses, such clauses \fBmust\fR match
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for any algorithm to even be under consideration.
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The third clause represents an optional clause.
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Matching such clauses is not a requirement, but any additional optional
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match counts in favor of the algorithm.
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More details about that in the \fBLookups\fR section.
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A \fIproperty query\fR is a sequence of comma separated property query clauses.
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The full syntax for property queries appears below, but the available syntactic
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features are:
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.IP "\(bu" 4
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\&\fB=\fR is an infix operator providing an equality test.
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.IP "\(bu" 4
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\&\fB!=\fR is an infix operator providing an inequality test.
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.IP "\(bu" 4
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\&\fB?\fR is a prefix operator that means that the following clause is optional
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but preferred.
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.IP "\(bu" 4
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\&\fB\-\fR is a prefix operator that means any global query clause involving the
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following property name should be ignored.
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.IP "\(bu" 4
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\&\fB\*(L"...\*(R"\fR is a quoted string.
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The quotes are not included in the body of the string.
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.IP "\(bu" 4
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\&\fB'...'\fR is a quoted string.
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The quotes are not included in the body of the string.
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.SS "Lookups"
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.IX Subsection "Lookups"
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When an algorithm is looked up, a property query is used to determine
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the best matching algorithm.
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All mandatory query clauses \fBmust\fR be present and the implementation
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that additionally has the largest number of matching optional query
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clauses will be used.
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If there is more than one such optimal candidate, the result will be
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chosen from amongst those in an indeterminate way.
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Ordering of optional clauses is not significant.
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.SS "Shortcut"
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.IX Subsection "Shortcut"
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In order to permit a more concise expression of boolean properties, there
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is one short cut: a property name alone (e.g. \*(L"my.property\*(R") is
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exactly equivalent to \*(L"my.property=yes\*(R" in both definitions and queries.
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.SS "Global and Local"
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.IX Subsection "Global and Local"
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Two levels of property query are supported.
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A context based property query that applies to all fetch operations and a local
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property query.
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Where both the context and local queries include a clause with the same name,
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the local clause overrides the context clause.
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.PP
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It is possible for a local property query to remove a clause in the context
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property query by preceding the property name with a '\-'.
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For example, a context property query that contains \*(L"fips=yes\*(R" would normally
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result in implementations that have \*(L"fips=yes\*(R".
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.PP
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However, if the setting of the \*(L"fips\*(R" property is irrelevant to the
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operations being performed, the local property query can include the
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clause \*(L"\-fips\*(R".
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Note that the local property query could not use \*(L"fips=no\*(R" because that would
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disallow any implementations with \*(L"fips=yes\*(R" rather than not caring about the
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setting.
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.SH "SYNTAX"
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.IX Header "SYNTAX"
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The lexical syntax in \s-1EBNF\s0 is given by:
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.PP
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.Vb 11
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\& Definition ::= PropertyName ( \*(Aq=\*(Aq Value )?
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\& ( \*(Aq,\*(Aq PropertyName ( \*(Aq=\*(Aq Value )? )*
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\& Query ::= PropertyQuery ( \*(Aq,\*(Aq PropertyQuery )*
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\& PropertyQuery ::= \*(Aq\-\*(Aq PropertyName
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\& | \*(Aq?\*(Aq? ( PropertyName (( \*(Aq=\*(Aq | \*(Aq!=\*(Aq ) Value)?)
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\& Value ::= NumberLiteral | StringLiteral
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\& StringLiteral ::= QuotedString | UnquotedString
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\& QuotedString ::= \*(Aq"\*(Aq [^"]* \*(Aq"\*(Aq | "\*(Aq" [^\*(Aq]* "\*(Aq"
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\& UnquotedString ::= [^{space},]+
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\& NumberLiteral ::= \*(Aq0\*(Aq ( [0\-7]* | \*(Aqx\*(Aq [0\-9A\-Fa\-f]+ ) | \*(Aq\-\*(Aq? [1\-9] [0\-9]+
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\& PropertyName ::= [A\-Z] [A\-Z0\-9_]* ( \*(Aq.\*(Aq [A\-Z] [A\-Z0\-9_]* )*
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.Ve
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.SH "HISTORY"
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.IX Header "HISTORY"
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Properties were added in OpenSSL 3.0
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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