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<a href="https://gitlab.com/nmav">Nikos Mavrogiannopoulos</a>
commented on a discussion
on <a href="https://gitlab.com/gnutls/gnutls/merge_requests/711#note_90800941">lib/handshake-tls13.c</a>:
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<td class="diff-line-num new new_line" data-linenumber="407" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: 0 5px;" align="right" bgcolor="#ddfbe6">
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<pre style="margin: 0;">+<span id="LC407" class="line" lang="c"> <span class="n" style="color: #333;">IMED_RET</span><span class="p">(</span><span class="s" style="color: #d14;">"generate app keys"</span><span class="p">,</span> <span class="n" style="color: #333;">ret</span><span class="p">,</span> <span class="mi" style="color: #099;">0</span><span class="p">);</span></span>
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<td class="diff-line-num new new_line" data-linenumber="408" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: 0 5px;" align="right" bgcolor="#ddfbe6">
408
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<pre style="margin: 0;">+<span id="LC408" class="line" lang="c"></span>
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<pre style="margin: 0;">+<span id="LC409" class="line" lang="c"> <span class="n" style="color: #333;">ret</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">_tls13_write_connection_state_init</span><span class="p">(</span><span class="n" style="color: #333;">session</span><span class="p">,</span> <span class="n" style="color: #333;">STAGE_APP</span><span class="p">);</span></span>
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<td class="diff-line-num new new_line" data-linenumber="410" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: 0 5px;" align="right" bgcolor="#ddfbe6">
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<pre style="margin: 0;">+<span id="LC410" class="line" lang="c"> <span class="n" style="color: #333;">IMED_RET</span><span class="p">(</span><span class="s" style="color: #d14;">"set write app keys"</span><span class="p">,</span> <span class="n" style="color: #333;">ret</span><span class="p">,</span> <span class="mi" style="color: #099;">0</span><span class="p">);</span></span>
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<td class="diff-line-num new new_line" data-linenumber="411" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: 0 5px;" align="right" bgcolor="#ddfbe6">
411
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<pre style="margin: 0;">+<span id="LC411" class="line" lang="c"></span>
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<td class="diff-line-num new new_line" data-linenumber="412" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: 0 5px;" align="right" bgcolor="#ddfbe6">
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<pre style="margin: 0;">+<span id="LC412" class="line" lang="c"> <span class="n" style="color: #333;">_gnutls_handshake_log</span><span class="p">(</span><span class="s" style="color: #d14;">"HSK[%p]: switching early to application traffic keys</span><span class="se" style="color: #d14;">\n</span><span class="s" style="color: #d14;">"</span><span class="p">,</span> <span class="n" style="color: #333;">session</span><span class="p">);</span></span>
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<pre style="margin: 0;">+<span id="LC413" class="line" lang="c"> <span class="p">}</span></span>
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<pre style="margin: 0;">+<span id="LC414" class="line" lang="c"></span>
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<pre style="margin: 0;">+<span id="LC415" class="line" lang="c"> <span class="cm" style="color: #998; font-style: italic;">/* fall through */</span></span>
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<pre style="margin: 0;">+<span id="LC416" class="line" lang="c"> <span class="k" style="font-weight: 600;">case</span> <span class="n" style="color: #333;">STATE108</span><span class="p">:</span></span>
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<pre style="margin: 0;">+<span id="LC417" class="line" lang="c"> <span class="k" style="font-weight: 600;">if</span> <span class="p">(</span><span class="n" style="color: #333;">session</span><span class="o" style="font-weight: 600;">-></span><span class="n" style="color: #333;">internals</span><span class="p">.</span><span class="n" style="color: #333;">resumed</span> <span class="o" style="font-weight: 600;">!=</span> <span class="n" style="color: #333;">RESUME_FALSE</span><span class="p">)</span></span>
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<pre style="margin: 0;">+<span id="LC418" class="line" lang="c"> <span class="n" style="color: #333;">_gnutls_set_resumed_parameters</span><span class="p">(</span><span class="n" style="color: #333;">session</span><span class="p">);</span></span>
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<pre style="margin: 0;">+<span id="LC419" class="line" lang="c"></span>
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<pre style="margin: 0;">+<span id="LC420" class="line" lang="c"> <span class="cm" style="color: #998; font-style: italic;">/* If we didn't request a client certificate we can send tickets now</span></span>
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<pre style="margin: 0;">+<span id="LC421" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> * and return early */</span></span>
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<pre style="margin: 0;">+<span id="LC422" class="line" lang="c"> <span class="k" style="font-weight: 600;">if</span> <span class="p">(</span><span class="n" style="color: #333;">session</span><span class="o" style="font-weight: 600;">-></span><span class="n" style="color: #333;">internals</span><span class="p">.</span><span class="n" style="color: #333;">hsk_flags</span> <span class="o" style="font-weight: 600;">&</span> <span class="n" style="color: #333;">HSK_EARLY_START_USED</span><span class="p">)</span> <span class="p">{</span></span>
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<p dir="auto">What do you have in mind? The sending of the ticket early, is an improvement to the current situation as it allows the client to have it in cache/queue when the handshake is complete. It is described in the TLS1.3 as:</p>
<pre class="code highlight js-syntax-highlight plaintext" lang="plaintext" v-pre="true" style="background-color: #fff; font-family: monospace; font-size: 90%; -premailer-cellpadding: 0; -premailer-cellspacing: 0; -premailer-width: 100%; margin: 0;"><code><span id="LC1" class="line" lang="plaintext"> Although the resumption master secret depends on the client's</span>
<span id="LC2" class="line" lang="plaintext"> second flight, servers which do not request client authentication MAY</span>
<span id="LC3" class="line" lang="plaintext"> compute the remainder of the transcript independently and then send a</span>
<span id="LC4" class="line" lang="plaintext"> NewSessionTicket immediately upon sending its Finished rather than</span>
<span id="LC5" class="line" lang="plaintext"> waiting for the client Finished. This might be appropriate in cases</span>
<span id="LC6" class="line" lang="plaintext"> where the client is expected to open multiple TLS connections in</span>
<span id="LC7" class="line" lang="plaintext"> parallel and would benefit from the reduced overhead of a resumption</span>
<span id="LC8" class="line" lang="plaintext"> handshake, for example.</span></code></pre>
<p dir="auto">The worrying part is point 2 from 4.4.4:</p>
<pre class="code highlight js-syntax-highlight plaintext" lang="plaintext" v-pre="true" style="background-color: #fff; font-family: monospace; font-size: 90%; -premailer-cellpadding: 0; -premailer-cellspacing: 0; -premailer-width: 100%; margin: 0;"><code><span id="LC1" class="line" lang="plaintext"> Servers MAY send data after sending their first flight, but</span>
<span id="LC2" class="line" lang="plaintext"> because the handshake is not yet complete, they have no assurance</span>
<span id="LC3" class="line" lang="plaintext"> of either the peer's identity or of its liveness</span></code></pre>
<p dir="auto">but as we are only doing that for the "unauthenticated client" it shouldn't matter.</p>
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