Application-Layer Protocol Negotiation
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Application-Layer Protocol Negotiation (ALPN) is a Transport Layer Security (TLS) extension that allows the application layer to negotiate which protocol should be performed over a secure connection in a manner that avoids additional round trips and which is independent of the application-layer protocols. It is used to establish HTTP/2 connections without additional round trips (client and server can communicate over two ports previously assigned to HTTPS with HTTP/1.1 and upgrade to use HTTP/2 or continue with HTTP/1.1 without closing the initial connection).
Support
[edit]ALPN is supported by these libraries:
- BSAFE Micro Edition Suite since version 5.0[1]
- GnuTLS since version 3.2.0 released in May 2013[2]
- MatrixSSL since version 3.7.1 released in December 2014[3]
- Network Security Services since version 3.15.5 released in April 2014[4]
- OpenSSL since version 1.0.2 released in January 2015[5]
- LibreSSL since version 2.1.3 released in January 2015[6]
- mbed TLS (previously PolarSSL) since version 1.3.6 released in April 2014[7]
- s2n since its original public release in June 2015.
- wolfSSL (formerly CyaSSL) since version 3.7.0 released in October 2015[8]
- Go (in the standard library crypto/tls package) since version 1.4 released in December 2014[9]
- JSSE in Java since JDK 9 released in September 2017,[10] backported to JDK 8 released in April 2020[11]
- Win32 SSPI since Windows 8.1 and Windows Server 2012 R2 were released October 18, 2013[12]
History
[edit]Next Protocol Negotiation
[edit]In January 2010, Google introduced IETF standard draft describing Next Protocol Negotiation TLS extension.[13] 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.
Application-Layer Protocol Negotiation
[edit]On July 11, 2014, ALPN was published as RFC 7301. ALPN replaces Next Protocol Negotiation (NPN) extension.[14]
TLS False Start was disabled in Google Chrome from version 20 (2012) onward except for websites with the earlier NPN extension.[15]
Example
[edit]ALPN is a TLS extension which is sent on the initial TLS handshake 'Client Hello', and it lists the protocols that the client (for example the web browser) supports:
Handshake Type: Client Hello (1)
Length: 141
Version: TLS 1.2 (0x0303)
Random: dd67b8633e5efd0740519f38071008b59efbd68ab3114587...
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
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:
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
References
[edit]- ^ "Dell BSAFE Micro Edition Suite 5.0 Release Advisory". Retrieved 2022-10-18.
- ^ "gnutls 3.2.0". Archived from the original on 2016-01-31. Retrieved 2015-01-26.
- ^ "MatrixSSL - News". 2014-12-04. Archived from the original on 2015-02-14. Retrieved 2015-01-26.
- ^ "NSS 3.15.5 release notes". Mozilla Developer Network. Mozilla. Retrieved 2015-01-26.
- ^ "OpenSSL 1.0.2 release notes". The OpenSSL Project. 2015-01-22. Archived from the original on 2014-09-04. Retrieved 2015-01-26.
- ^ "LibreSSL 2.1.3 released". 2015-01-22. Retrieved 2015-01-26.
- ^ "Download overview - PolarSSL". 2014-04-11. Archived from the original on 2015-02-09. Retrieved 2015-01-26.
- ^ "wolfSSL Release Change Log". 2015-10-26. Retrieved 2015-09-11.
- ^ "Go 1.4 Release Notes". 2014-12-10. Retrieved 2017-11-28.
- ^ "JEP 244: TLS Application-Layer Protocol Negotiation Extension". 2017-08-07. Retrieved 2018-08-29.
- ^ "Release Note: TLS Application-Layer Protocol Negotiation Extension". 2020-04-30. Retrieved 2020-06-11.
- ^ "What's New in TLS/SSL (Schannel SSP)". 31 August 2016. Retrieved 2020-03-30.
- ^ Langley, A. (January 20, 2010). "Transport Layer Security (TLS) Next Protocol Negotiation Extension". IETF Datatracker.
- ^ Langley, Adam. "» NPN and ALPN". Retrieved 2 April 2013.
- ^ Langley, Adam. "False Start's Failure (11 Apr 2012)". Retrieved 25 September 2013.
External links
[edit]- The registry of ALPN protocol IDs is maintained by IANA as a TLS extension.
- draft-agl-tls-nextprotoneg-04 (NPN draft) (last updated: May 2012)
- RFC 7301 "Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension"