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Application-Layer Protocol Negotiation
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<h2 id="support">Support</h2> <p>ALPN is supported by these libraries: </p> <ul><li><a href="/facts/BSAFE/Av5SNJ7x">BSAFE</a> Micro Edition Suite since version 5.0<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a></li> <li><a href="/facts/GnuTLS/y3fYe3RI">GnuTLS</a> since version 3.2.0 released in May 2013<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a></li> <li><a href="/facts/MatrixSSL/STIFbzgl">MatrixSSL</a> since version 3.7.1 released in December 2014<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a></li> <li><a href="/facts/Network_Security_Services/y7bq3SV2">Network Security Services</a> since version 3.15.5 released in April 2014<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a></li> <li><a href="/facts/OpenSSL/aXvs5fo2">OpenSSL</a> since version 1.0.2 released in January 2015<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a></li> <li><a href="/facts/LibreSSL/9UnXD0lm">LibreSSL</a> since version 2.1.3 released in January 2015<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a></li> <li><a href="/facts/Mbed_TLS/33AV5voW">mbed TLS</a> (previously PolarSSL) since version 1.3.6 released in April 2014<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a></li> <li><a href="/facts/S2n/erxqccsw">s2n</a> since its original public release in June 2015.</li> <li><a href="/facts/WolfSSL/26UD7dQE">wolfSSL</a> (formerly CyaSSL) since version 3.7.0 released in October 2015<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a></li> <li><a href="/facts/Go_(programming_language)/oWlsmAFJ">Go</a> (in the standard library crypto/tls package) since version 1.4 released in December 2014<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a></li> <li><a href="/facts/Java_Secure_Socket_Extension/0uryvVja">JSSE</a> in <a href="/facts/Java_(software_platform)/fpn6x8WL">Java</a> since JDK 9 released in September 2017,<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> backported to JDK 8 released in April 2020<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a></li> <li><a href="/facts/Security_Support_Provider_Interface/lIeS9tug">Win32 SSPI</a> since Windows 8.1 and Windows Server 2012 R2 were released October 18, 2013<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a></li></ul> <h2 id="history">History</h2> <h3>Next Protocol Negotiation</h3> <p>In January 2010, Google introduced IETF standard draft describing Next Protocol Negotiation TLS extension.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> This extension was used to negotiate experimental SPDY connections between Google Chrome and some of Google's servers. As SPDY evolved, NPN was replaced with ALPN. </p> <h3>Application-Layer Protocol Negotiation</h3> <p>On July 11, 2014, ALPN was published as <a href="/facts/RFC_(identifier)/esftTvE7">RFC</a> <a href="https://www.rfc-editor.org/rfc/rfc7301">7301</a>. ALPN replaces Next Protocol Negotiation (NPN) extension.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p><p><a href="/facts/TLS_False_Start/pGy16TnA">TLS False Start</a> was disabled in <a href="/facts/Google_Chrome/4INfWq37">Google Chrome</a> from version 20 (2012) onward except for websites with the earlier NPN extension.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> </p> <h2 id="example">Example</h2> <p>ALPN is a TLS extension which is sent on the initial <a href="/facts/Transport_Layer_Security/pGy16TnA">TLS handshake</a> 'Client Hello', and it lists the protocols that the client (for example the web browser) supports: </p> Handshake Type: Client Hello (1) Length: 141 Version: TLS 1.2 (0x0303) Random: dd67b5943e5efd0740519f38071008b59efbd68ab3114587... Session ID Length: 0 Cipher Suites Length: 10 Cipher Suites (5 suites) Compression Methods Length: 1 Compression Methods (1 method) Extensions Length: 90 [other extensions omitted] Extension: application_layer_protocol_negotiation (len=14) Type: application_layer_protocol_negotiation (16) Length: 14 ALPN Extension Length: 12 ALPN Protocol ALPN string length: 2 ALPN Next Protocol: h2 ALPN string length: 8 ALPN Next Protocol: http/1.1 <p>The resulting 'Server Hello' from the web server will also contain the ALPN extension, and it confirms which protocol will be used for the HTTP request: </p> Handshake Type: Server Hello (2) Length: 94 Version: TLS 1.2 (0x0303) Random: 44e447964d7e8a7d3b404c4748423f02345241dcc9c7e332... Session ID Length: 32 Session ID: 7667476d1d698d0a90caa1d9a449be814b89a0b52f470e2d... Cipher Suite: TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (0xc02f) Compression Method: null (0) Extensions Length: 22 [other extensions omitted] Extension: application_layer_protocol_negotiation (len=5) Type: application_layer_protocol_negotiation (16) Length: 5 ALPN Extension Length: 3 ALPN Protocol ALPN string length: 2 ALPN Next Protocol: h2 <h2 id="external-links">External links</h2> <ul><li><a href="https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xhtml#alpn-protocol-ids">The registry of ALPN protocol IDs is maintained by IANA as a TLS extension.</a></li> <li><a href="https://tools.ietf.org/html/draft-agl-tls-nextprotoneg-04">draft-agl-tls-nextprotoneg-04 (NPN draft)</a> (last updated: May 2012)</li> <li><a href="/facts/RFC_(identifier)/esftTvE7">RFC</a> <a href="https://www.rfc-editor.org/rfc/rfc7301">7301</a> "Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension"</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Dell BSAFE Micro Edition Suite 5.0 Release Advisory". Retrieved 2022-10-18. <a href="https://www.dell.com/support/kbdoc/000204231/dell-bsafe-micro-edition-suite-5-0-release-advisory" target="_blank">https://www.dell.com/support/kbdoc/000204231/dell-bsafe-micro-edition-suite-5-0-release-advisory</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"gnutls 3.2.0". Archived from the original on 2016-01-31. Retrieved 2015-01-26. <a href="https://web.archive.org/web/20160131230710/http://article.gmane.org/gmane.network.gnutls.general/3136" target="_blank">https://web.archive.org/web/20160131230710/http://article.gmane.org/gmane.network.gnutls.general/3136</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"MatrixSSL - News". 2014-12-04. Archived from the original on 2015-02-14. Retrieved 2015-01-26. <a href="https://web.archive.org/web/20150214105056/http://www.matrixssl.org/news.html" target="_blank">https://web.archive.org/web/20150214105056/http://www.matrixssl.org/news.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"NSS 3.15.5 release notes". Mozilla Developer Network. Mozilla. Retrieved 2015-01-26. <a href="https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/NSS_3.15.5_release_notes" target="_blank">https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/NSS_3.15.5_release_notes</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"OpenSSL 1.0.2 release notes". The OpenSSL Project. 2015-01-22. Archived from the original on 2014-09-04. Retrieved 2015-01-26. <a href="https://web.archive.org/web/20140904045720/http://www.openssl.org/news/openssl-1.0.2-notes.html" target="_blank">https://web.archive.org/web/20140904045720/http://www.openssl.org/news/openssl-1.0.2-notes.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>"LibreSSL 2.1.3 released". 2015-01-22. Retrieved 2015-01-26. <a href="https://marc.info/?l=openbsd-announce&m=142193407304782" target="_blank">https://marc.info/?l=openbsd-announce&m=142193407304782</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"Download overview - PolarSSL". 2014-04-11. Archived from the original on 2015-02-09. Retrieved 2015-01-26. <a href="https://web.archive.org/web/20150209195111/https://polarssl.org/tech-updates/releases/polarssl-1.3.6-released" target="_blank">https://web.archive.org/web/20150209195111/https://polarssl.org/tech-updates/releases/polarssl-1.3.6-released</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"wolfSSL Release Change Log". 2015-10-26. Retrieved 2015-09-11. <a href="https://www.wolfssl.com/wolfSSL/Docs-wolfssl-changelog.html" target="_blank">https://www.wolfssl.com/wolfSSL/Docs-wolfssl-changelog.html</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"Go 1.4 Release Notes". 2014-12-10. Retrieved 2017-11-28. <a href="https://golang.org/doc/go1.4#minor_library_changes" target="_blank">https://golang.org/doc/go1.4#minor_library_changes</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"JEP 244: TLS Application-Layer Protocol Negotiation Extension". 2017-08-07. Retrieved 2018-08-29. <a href="https://bugs.openjdk.java.net/browse/JDK-8051498" target="_blank">https://bugs.openjdk.java.net/browse/JDK-8051498</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>"Release Note: TLS Application-Layer Protocol Negotiation Extension". 2020-04-30. Retrieved 2020-06-11. <a href="https://bugs.openjdk.java.net/browse/JDK-8242894" target="_blank">https://bugs.openjdk.java.net/browse/JDK-8242894</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>"What's New in TLS/SSL (Schannel SSP)". 31 August 2016. Retrieved 2020-03-30. <a href="https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-R2-and-2012/hh831771(v=ws.11)?redirectedfrom=MSDN#whats-new-in-tlsssl-schannel-ssp-in-windows-server-2012-r2-and-windows-81" target="_blank">https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-R2-and-2012/hh831771(v=ws.11)?redirectedfrom=MSDN#whats-new-in-tlsssl-schannel-ssp-in-windows-server-2012-r2-and-windows-81</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Langley, A. (January 20, 2010). "Transport Layer Security (TLS) Next Protocol Negotiation Extension". IETF Datatracker. <a href="https://datatracker.ietf.org/doc/html/draft-agl-tls-nextprotoneg-00" target="_blank">https://datatracker.ietf.org/doc/html/draft-agl-tls-nextprotoneg-00</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Langley, Adam. "» NPN and ALPN". Retrieved 2 April 2013. <a href="https://www.imperialviolet.org/2013/03/20/alpn.html" target="_blank">https://www.imperialviolet.org/2013/03/20/alpn.html</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Langley, Adam. "False Start's Failure (11 Apr 2012)". Retrieved 25 September 2013. <a href="https://www.imperialviolet.org/2012/04/11/falsestart.html" target="_blank">https://www.imperialviolet.org/2012/04/11/falsestart.html</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> </ol>