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Support per-hash options and remove MIME type support #236

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Apr 8, 2015
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Merged

Support per-hash options and remove MIME type support #236

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fbf2055
Added note on content negotiation.
joelweinberger Apr 2, 2015
f6e9398
Specify that the omission will have to be a type option-expression.
joelweinberger Apr 2, 2015
54e31a1
Changed integrity productions to reflect per-hash-expression options …
joelweinberger Apr 8, 2015
beec679
Got rid of MIME type references, other than note that they may be add…
joelweinberger Apr 8, 2015
7b00748
Modified metadata algorithm to generate a set of strong hashes.
joelweinberger Apr 8, 2015
1079297
MIME type fix
joelweinberger Apr 8, 2015
ba61d24
Merge remote-tracking branch 'upstream/master' into mention-content-neg
joelweinberger Apr 8, 2015
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115 changes: 56 additions & 59 deletions specs/subresourceintegrity/index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -143,11 +143,10 @@ <h2 id="introduction">Introduction</h2>
<code>script</code> element, like so:</p>

<pre><code>&lt;script src="https://code.jquery.com/jquery-1.10.2.min.js"
integrity="type=application/javascript
sha256-C6CB9UYIS9UJeqinPHWTHVqh/E1uhG5Twh+Y5qFQmYg="&gt;
integrity="sha256-C6CB9UYIS9UJeqinPHWTHVqh/E1uhG5Twh+Y5qFQmYg="&gt;
</code></pre>

<p class="example highlight">Scripts, of course, are not the only resource type which would benefit
<p>Scripts, of course, are not the only resource type which would benefit
from integrity validation. The scheme specified here applies to all HTML
elements which trigger fetches, as well as to fetches triggered from CSS
and JavaScript.</p>
Expand Down Expand Up @@ -192,7 +191,7 @@ <h4 id="resource-integrity">Resource Integrity</h4>
<a href="#dfn-integrity-metadata">integrity metadata</a> to the <code>link</code> element included on her page:</p>

<pre class="example highlight"><code>&lt;link rel="stylesheet" href="https://site53.cdn.net/style.css"
integrity="type=text/css sha256-SDfwewFAE...wefjijfE"&gt;
integrity="sha256-SDfwewFAE...wefjijfE"&gt;
</code></pre>
</li>
<li>
Expand All @@ -203,8 +202,7 @@ <h4 id="resource-integrity">Resource Integrity</h4>
adding it to the <code>script</code> element she includes on her page:</p>

<pre class="example highlight"><code>&lt;script src="https://analytics-r-us.com/v1.0/include.js"
integrity="type=application/javascript
sha256-SDfwewFAE...wefjijfE"&gt;&lt;/script&gt;
integrity="sha256-SDfwewFAE...wefjijfE"&gt;&lt;/script&gt;
</code></pre>
</li>
<li>
Expand Down Expand Up @@ -256,11 +254,8 @@ <h3 id="key-concepts-and-terminology">Key Concepts and Terminology</h3>
Content</a> specification. An example of a potentially secure origin
is an origin whose scheme component is <code>HTTPS</code>.</p>

<p>The <dfn>MIME type</dfn> of a resource is a technical hint about the use
and format of that resource. [[!MIMETYPE]]</p>

<p>The <dfn>message body</dfn> and the <dfn>transfer encoding</dfn> of a resource
are defined by <a href="http://tools.ietf.org/html/rfc7230#section-3">RFC7230, section 3</a>. [[!RFC7230]]</p>
are defined by <a href="http://tools.ietf.org/html/rfc7230#section-3">RFC7230, section 3</a>. [[!RFC7230]] </p>

<p>The <dfn>representation data</dfn> and <dfn>content encoding</dfn> of a resource
are defined by <a href="http://tools.ietf.org/html/rfc7231#section-3">RFC7231, section 3</a>. [[!RFC7231]]</p>
Expand Down Expand Up @@ -295,12 +290,10 @@ <h3 id="integrity-metadata">Integrity metadata</h3>
<ul>
<li>cryptographic hash function (“alg”)</li>
<li><a href="#dfn-digest">digest</a> (“val”)</li>
<li>the resource’s <a href="#dfn-mime-type">MIME type</a> (“type”)</li>
</ul>

<p>The hash function and digest MUST be provided in order to validate a
resource’s integrity. The MIME type SHOULD be provided, as it mitigates the
risk of certain attack vectors.</p>
resource’s integrity.</p>

<p>This metadata MUST be encoded in the same format as the <code>hash-source</code>
in <a href="http://www.w3.org/TR/CSP11/#source-list-syntax">section 4.2 of the Content Security Policy Level 2 specification</a>.</p>
Expand All @@ -313,11 +306,6 @@ <h3 id="integrity-metadata">Integrity metadata</h3>
<pre class="example highlight"><code>sha256-qznLcsROx4GACP2dm0UCKCzCG+HiZ1guq6ZZDob/Tng=
</code></pre>

<p>Or, if the author further wishes to specify the Content Type (<code>application/javascript</code>):</p>

<pre class="example highlight"><code>type=application/javascript sha256-qznLcsROx4GACP2dm0UCKCzCG+HiZ1guq6ZZDob/Tng=
</code></pre>

<div class="note">
<p>Digests may be generated using any number of utilities. <a href="http://www.openssl.org/">OpenSSL</a>, for
example, is quite commonly available. The example in this section is the
Expand Down Expand Up @@ -353,9 +341,8 @@ <h4 id="agility">Agility</h4>
<p>Authors may choose to specify both, for example:</p>

<pre><code>&lt;script src="hello_world.js"
integrity="type=application/javascript
sha256-+MO/YqmqPm/BYZwlDkir51GTc9Pt9BvmLrXcRRma8u8=
sha512-rQw3wx1psxXzqB8TyM3nAQlK2RcluhsNwxmcqXE2YbgoDW735o8TPmIR4uWpoxUERddvFwjgRSGw7gNPCwuvJg==
integrity="sha256-+MO/YqmqPm/BYZwlDkir51GTc9Pt9BvmLrXcRRma8u8=
sha512-rQw3wx1psxXzqB8TyM3nAQlK2RcluhsNwxmcqXE2YbgoDW735o8TPmIR4uWpoxUERddvFwjgRSGw7gNPCwuvJg==
"&gt;&lt;/script&gt;
</code></pre>

Expand All @@ -379,15 +366,14 @@ <h4 id="agility">Agility</h4>
<section>
<h4 id="priority">Priority</h4>

<p>User agents MUST provide a mechanism of determining the relative priority of
two hash functions. That is, if a user agent implemented a function like
<dfn>getPrioritizedHashFunction(a, b)</dfn> it would return the hash function
the user agent considers the most collision-resistant.
For example, <code>getPrioritizedHashFunction('SHA-256', 'SHA-512')</code> would return
<code>SHA-512</code>.</p>
<p>User agents MUST provide a mechanism of determining the relative priority of two
hash functions and return the empty string if the priority is equal. That is, if
a user agent implemented a function like <dfn>getPrioritizedHashFunction(a,
b)</dfn> it would return the hash function the user agent considers the most
collision-resistant. For example, <code>getPrioritizedHashFunction('SHA-256',
'SHA-512')</code> would return <code>SHA-512</code> and <code>getPrioritizedHashFunction('SHA-256',
'SHA-256')</code> would return the empty string.</p>

<p>If both algorithms are equally strong, the user agent SHOULD ensure that there
is a consistent ordering.</p>
</section>
<!-- /Framework::Cryptographic hash functions::Priority -->

Expand Down Expand Up @@ -510,22 +496,25 @@ <h4 id="parse-varmetadatavar">Parse <var>metadata</var>.</h4>
<h4 id="get-the-strongest-metadata-from-varsetvar">Get the strongest metadata from <var>set</var>.</h4>

<ol>
<li>Let <var>strongest</var> be the empty string.</li>
<li>Let <var>result</var> be the empty set and <var>strongest</var> be the empty
string.</li>
<li>For each <var>item</var> in <var>set</var>:
<ol>
<li>If <var>strongest</var> is the empty string, set <var>strongest</var>
to <var>item</var>, skip to the next
<var>item</var>.</li>
<li>If <var>result</var> is the empty set, add <var>item</var> to
<var>result</var> and set <var>strongest</var> to <var>item</var>, skip
to the next <var>item</var>.</li>
<li>Let <var>currentAlgorithm</var> be the <var>alg</var> component of
<var>strongest</var>.</li>
<li>Let <var>newAlgorithm</var> be the <var>alg</var> component of
<var>item</var>.</li>
<li>If the result of <a href="#dfn-getprioritizedhashfunction-a-b"><code>getPrioritizedHashFunction(currentAlgorithm, newAlgorithm)</code></a>
is <var>newAlgorithm</var>, set <var>strongest</var> to
<var>item</var>.</li>
is the empty string, add <var>item</var> to <var>result</var>. If the
result is <var>newAlgorithm</var>, set <var>strongest</var> to
<var>item</var>, set <var>result</var> to the empty set, and add
<var>item</var> to <var>result</var>.</li>
</ol>
</li>
<li>Return <var>strongest</var>.</li>
<li>Return <var>result</var>.</li>
</ol>

</section>
Expand All @@ -542,24 +531,32 @@ <h4 id="does-varresourcevar-match-varmetadatalistvar">Does <var>resource</var> m
<li>If <var>parsedMetadata</var> is <code>no metadata</code>, return <code>true</code>.</li>
<li>Let <var>metadata</var> be the result of <a href="#get-the-strongest-metadata-from-set.x">getting the strongest
metadata from <var>parsedMetadata</var></a>.</li>
<li>Let <var>algorithm</var> be the <var>alg</var> component of
<var>metadata</var>.</li>
<li>Let <var>expectedValue</var> be the <var>val</var> component of
<li>For each <var>item</var> in <var>metadata</var>:
<ol>
<li>Let <var>algorithm</var> be the <var>alg</var> component of
<var>metadata</var>.</li>
<li>Let <var>expectedType</var> be the <var>type</var> component of
<li>Let <var>expectedValue</var> be the <var>val</var> component of
<var>metadata</var>.</li>
<li>If <var>expectedType</var> is not the empty string, and is not a
case-insensitive match for <var>resource</var>’s <a href="#dfn-mime-type">MIME type</a>,
return <code>false</code>.</li>
<li>Let <var>actualValue</var> be the result of <a href="#apply-algorithm-to-resource">applying
<li>Let <var>actualValue</var> be the result of <a href="#apply-algorithm-to-resource">applying
<var>algorithm</var> to <var>resource</var></a>.</li>
<li>If <var>actualValue</var> is a case-sensitive match for
<var>expectedValue</var>, return <code>true</code>. Otherwise, return <code>false</code>.</li>
<li>If <var>actualValue</var> is a case-sensitive match for
<var>expectedValue</var>, return <code>true</code>.</li>
</ol>
</li>
<li>Return <code>false</code>.</li>
</ol>

<p class="note">If <var>expectedType</var> is the empty string in #10, it would
be reasonable for the user agent to warn the page’s author about the
dangers of MIME type confusion attacks via its developer console.</p>
<p>This algorithm allows the user agent to accept multiple, valid strong hash
functions. For example, a developer might write a <code>script</code> element such as:</p>

<pre><code>&lt;script src="https://foobar.com/content-changes.js"
integrity="sha256-C6CB9UYIS9UJeqinPHWTHVqh/E1uhG5Twh+Y5qFQmYg=
sha256-qznLcsROx4GACP2dm0UCKCzCG+HiZ1guq6ZZDob/Tng="&gt;
</code></pre>

<p>which would allow the user agent to accept two different content payloads, one
of which matches the first SHA256 hash value and the other matches the second
SHA256 hash value.</p>

<p class="note">User agents may allow users to modify the result of this algorithm via user
preferences, bookmarklets, third-party additions to the user agent, and other
Expand Down Expand Up @@ -603,12 +600,6 @@ <h3 id="modifications-to-fetch">Modifications to Fetch</h3>
<ol>
<li>Set <var>response</var>’s integrity state to <code>pending</code>.</li>
<li>Include a <code>Cache-Control</code> header whose value is “no-transform”.</li>
<li>If <var>request</var>’s integrity metadata contains a Content Type:
<ol>
<li>Set <var>request</var>’s <code>Accept</code> header value to the value
of <var>request</var>’s integrity metadata’s Content Type.</li>
</ol>
</li>
</ol>
</li>
</ol>
Expand Down Expand Up @@ -674,7 +665,8 @@ <h4 id="the-integrity-attribute">The <code>integrity</code> attribute</h4>
The value of the attribute MUST be either the empty string, or at least one
valid metadata as described by the following ABNF grammar:</p>

<pre><code>integrity-metadata = *WSP [ option-expression *( 1*WSP option-expression ) 1*WSP ] hash-expression *( 1*WSP hash-expression ) *WSP / *WSP
<pre><code>integrity-metadata = *WSP hash-with-options *( 1*WSP hash-with-options ) *WSP / *WSP
hash-with-options = hash-expression *("?" option-expression)
option-expression = option-name "=" option-value
option-name = 1*option-name-char
option-name-char = ALPHA / DIGIT / "-"
Expand All @@ -685,11 +677,16 @@ <h4 id="the-integrity-attribute">The <code>integrity</code> attribute</h4>
hash-expression = hash-algo "-" base64-value
</code></pre>

<p>At the moment, the only option-name that is defined is <code>type</code> and its
value must be a valid <a href="#dfn-mime-type">MIME type</a>.</p>

<p>The <code>integrity</code> IDL attribute must <a href="http://www.w3.org/TR/html5/infrastructure.html#reflect">reflect</a> the <code>integrity</code> content attribute.</p>

<p><code>option-expression</code>s are associated on a per <code>hash-expression</code> basis and are
applied only to the <code>hash-expression</code> that immediately precedes it.</p>

<div class="note">
<p>At the moment, no <code>option-expression</code>s are defined. However, future versions of
the spec make define options, such as MIME types [[!MIMETYPES]].</p>
</div>

</section>
<!-- /Framework::HTML::integrity -->

Expand Down
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