Security/Server Side TLS

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The goal of this document is to help operational teams with the configuration of TLS on servers. All Mozilla sites and deployment should follow the recommendations below.

The Operations Security (OpSec) team maintains this document as a reference guide to navigate the TLS landscape. It contains information on TLS protocols, known issues and vulnerabilities, configuration examples and testing tools. Changes are reviewed and merged by the OpSec team, and broadcasted to the various Operational teams.

Updates to this page should be submitted to the source repository on github.

If you are looking for the configuration generator, click the image below:

Server-side-tls-config-generator.png

Recommended configurations

Three configurations are recommended. Pick the right configuration depending on your audience. If you do not need backward compatibility, and are building a service for modern clients only (post Firefox 27/Chrome 22), then use the Modern configuration. Otherwise, prefer the Intermediate configuration. Use the Old backward compatible configuration only if your service will be accessed by very old clients, such as Windows XP IE6, or ancient libraries & bots.

Configuration Oldest compatible client
Modern Firefox 27, Chrome 30, IE 11 on Windows 7, Edge, Opera 17, Safari 9, Android 5.0, Java 8
Intermediate Firefox 1, Chrome 1, IE 7, Opera 5, Safari 1, Windows XP IE8, Android 2.3, Java 7
Old Windows XP IE6, Java 6


Older versions of OpenSSL may not return the full list of algorithms. AES-GCM and some ECDHE are fairly recent, and not present on most versions of OpenSSL shipped with Ubuntu or RHEL. This listing below was obtained from a freshly built OpenSSL. If your version of OpenSSL is old, unavailable ciphers will be discarded automatically. Always use the full ciphersuite and let OpenSSL pick the ones it supports.

The ordering of a ciphersuite is very important because it decides which algorithms are going to be selected in priority. Each level shows the list of algorithms returned by its ciphersuite. If you have to pick ciphers manually for your application, make sure you keep the ordering.

The ciphersuite numbers listed come from the IANA TLS Cipher Suite Registry. Previous versions of these recommendations included draft numbers for ECDHE-ECDSA-CHACHA20-POLY1305 (0xCC,0x14) and ECDHE-RSA-CHACHA20-POLY1305 (0xCC,0x13).

Modern compatibility

For services that don't need backward compatibility, the parameters below provide a higher level of security. This configuration is compatible with Firefox 27, Chrome 30, IE 11 on Windows 7, Edge, Opera 17, Safari 9, Android 5.0, and Java 8.

  • Ciphersuites: ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256
  • Versions: TLSv1.2
  • TLS curves: prime256v1, secp384r1, secp521r1
  • Certificate type: ECDSA
  • Certificate curve: prime256v1, secp384r1, secp521r1
  • Certificate signature: sha256WithRSAEncryption, ecdsa-with-SHA256, ecdsa-with-SHA384, ecdsa-with-SHA512
  • RSA key size: 2048 (if not ecdsa)
  • DH Parameter size: None (disabled entirely)
  • ECDH Parameter size: 256
  • HSTS: max-age=15768000
  • Certificate switching: None
0xC0,0x2C  -  ECDHE-ECDSA-AES256-GCM-SHA384  TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AESGCM(256)    Mac=AEAD
0xC0,0x30  -  ECDHE-RSA-AES256-GCM-SHA384    TLSv1.2  Kx=ECDH  Au=RSA    Enc=AESGCM(256)    Mac=AEAD
0xCC,0xA9  -  ECDHE-ECDSA-CHACHA20-POLY1305  TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=ChaCha20(256)  Mac=AEAD
0xCC,0xA8  -  ECDHE-RSA-CHACHA20-POLY1305    TLSv1.2  Kx=ECDH  Au=RSA    Enc=ChaCha20(256)  Mac=AEAD
0xC0,0x2B  -  ECDHE-ECDSA-AES128-GCM-SHA256  TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AESGCM(128)    Mac=AEAD
0xC0,0x2F  -  ECDHE-RSA-AES128-GCM-SHA256    TLSv1.2  Kx=ECDH  Au=RSA    Enc=AESGCM(128)    Mac=AEAD
0xC0,0x24  -  ECDHE-ECDSA-AES256-SHA384      TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AES(256)       Mac=SHA384
0xC0,0x28  -  ECDHE-RSA-AES256-SHA384        TLSv1.2  Kx=ECDH  Au=RSA    Enc=AES(256)       Mac=SHA384
0xC0,0x23  -  ECDHE-ECDSA-AES128-SHA256      TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AES(128)       Mac=SHA256
0xC0,0x27  -  ECDHE-RSA-AES128-SHA256        TLSv1.2  Kx=ECDH  Au=RSA    Enc=AES(128)       Mac=SHA256

Rationale:

  • AES256-GCM is prioritized above its 128 bits variant, and ChaCha20 because we assume that most modern devices support AESNI instructions and thus benefit from fast and constant time AES.
  • We recommend ECDSA certificates with P256 as other curves may not be supported everywhere. RSA signatures on ECDSA certificates are permitted because very few CAs sign with ECDSA at the moment.
  • DHE is removed entirely because it is slow in comparison with ECDHE, and all modern clients support elliptic curve key exchanges.
  • SHA1 signature algorithm is removed in favor of SHA384 for AES256 and SHA256 for AES128.

Intermediate compatibility (default)

For services that don't need compatibility with legacy clients (mostly WinXP), but still need to support a wide range of clients, this configuration is recommended. It is is compatible with Firefox 1, Chrome 1, IE 7, Opera 5 and Safari 1.

  • Ciphersuites: ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES256-SHA:ECDHE-ECDSA-DES-CBC3-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA:!DSS
  • Versions: TLSv1.2, TLSv1.1, TLSv1
  • TLS curves: prime256v1, secp384r1, secp521r1
  • Certificate type: RSA
  • Certificate curve: None
  • Certificate signature: sha256WithRSAEncryption
  • RSA key size: 2048
  • DH Parameter size: 2048
  • ECDH Parameter size: 256
  • HSTS: max-age=15768000
  • Certificate switching: None
0xCC,0xA9  -  ECDHE-ECDSA-CHACHA20-POLY1305  TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=ChaCha20(256)  Mac=AEAD
0xCC,0xA8  -  ECDHE-RSA-CHACHA20-POLY1305    TLSv1.2  Kx=ECDH  Au=RSA    Enc=ChaCha20(256)  Mac=AEAD
0xC0,0x2B  -  ECDHE-ECDSA-AES128-GCM-SHA256  TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AESGCM(128)    Mac=AEAD
0xC0,0x2F  -  ECDHE-RSA-AES128-GCM-SHA256    TLSv1.2  Kx=ECDH  Au=RSA    Enc=AESGCM(128)    Mac=AEAD
0xC0,0x2C  -  ECDHE-ECDSA-AES256-GCM-SHA384  TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AESGCM(256)    Mac=AEAD
0xC0,0x30  -  ECDHE-RSA-AES256-GCM-SHA384    TLSv1.2  Kx=ECDH  Au=RSA    Enc=AESGCM(256)    Mac=AEAD
0x00,0x9E  -  DHE-RSA-AES128-GCM-SHA256      TLSv1.2  Kx=DH    Au=RSA    Enc=AESGCM(128)    Mac=AEAD
0x00,0x9F  -  DHE-RSA-AES256-GCM-SHA384      TLSv1.2  Kx=DH    Au=RSA    Enc=AESGCM(256)    Mac=AEAD
0xC0,0x23  -  ECDHE-ECDSA-AES128-SHA256      TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AES(128)       Mac=SHA256
0xC0,0x27  -  ECDHE-RSA-AES128-SHA256        TLSv1.2  Kx=ECDH  Au=RSA    Enc=AES(128)       Mac=SHA256
0xC0,0x09  -  ECDHE-ECDSA-AES128-SHA         SSLv3    Kx=ECDH  Au=ECDSA  Enc=AES(128)       Mac=SHA1
0xC0,0x28  -  ECDHE-RSA-AES256-SHA384        TLSv1.2  Kx=ECDH  Au=RSA    Enc=AES(256)       Mac=SHA384
0xC0,0x13  -  ECDHE-RSA-AES128-SHA           SSLv3    Kx=ECDH  Au=RSA    Enc=AES(128)       Mac=SHA1
0xC0,0x24  -  ECDHE-ECDSA-AES256-SHA384      TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AES(256)       Mac=SHA384
0xC0,0x0A  -  ECDHE-ECDSA-AES256-SHA         SSLv3    Kx=ECDH  Au=ECDSA  Enc=AES(256)       Mac=SHA1
0xC0,0x14  -  ECDHE-RSA-AES256-SHA           SSLv3    Kx=ECDH  Au=RSA    Enc=AES(256)       Mac=SHA1
0x00,0x67  -  DHE-RSA-AES128-SHA256          TLSv1.2  Kx=DH    Au=RSA    Enc=AES(128)       Mac=SHA256
0x00,0x33  -  DHE-RSA-AES128-SHA             SSLv3    Kx=DH    Au=RSA    Enc=AES(128)       Mac=SHA1
0x00,0x6B  -  DHE-RSA-AES256-SHA256          TLSv1.2  Kx=DH    Au=RSA    Enc=AES(256)       Mac=SHA256
0x00,0x39  -  DHE-RSA-AES256-SHA             SSLv3    Kx=DH    Au=RSA    Enc=AES(256)       Mac=SHA1
0xC0,0x08  -  ECDHE-ECDSA-DES-CBC3-SHA       SSLv3    Kx=ECDH  Au=ECDSA  Enc=3DES(168)      Mac=SHA1
0xC0,0x12  -  ECDHE-RSA-DES-CBC3-SHA         SSLv3    Kx=ECDH  Au=RSA    Enc=3DES(168)      Mac=SHA1
0x00,0x16  -  EDH-RSA-DES-CBC3-SHA           SSLv3    Kx=DH    Au=RSA    Enc=3DES(168)      Mac=SHA1
0x00,0x9C  -  AES128-GCM-SHA256              TLSv1.2  Kx=RSA   Au=RSA    Enc=AESGCM(128)    Mac=AEAD
0x00,0x9D  -  AES256-GCM-SHA384              TLSv1.2  Kx=RSA   Au=RSA    Enc=AESGCM(256)    Mac=AEAD
0x00,0x3C  -  AES128-SHA256                  TLSv1.2  Kx=RSA   Au=RSA    Enc=AES(128)       Mac=SHA256
0x00,0x3D  -  AES256-SHA256                  TLSv1.2  Kx=RSA   Au=RSA    Enc=AES(256)       Mac=SHA256
0x00,0x2F  -  AES128-SHA                     SSLv3    Kx=RSA   Au=RSA    Enc=AES(128)       Mac=SHA1
0x00,0x35  -  AES256-SHA                     SSLv3    Kx=RSA   Au=RSA    Enc=AES(256)       Mac=SHA1
0x00,0x0A  -  DES-CBC3-SHA                   SSLv3    Kx=RSA   Au=RSA    Enc=3DES(168)      Mac=SHA1

Rationale:

  • ChaCha20 is prefered as the fastest and safest in-software cipher, followed by AES128. Unlike the modern configuration, we do not assume clients support AESNI and thus do not prioritize AES256 above 128 and ChaCha20. There has been discussions (1, 2) on whether AES256 extra security was worth its computing cost in software (without AESNI), and the results are far from obvious. At the moment, AES128 is preferred, because it provides good security, is really fast, and seems to be more resistant to timing attacks.
  • DES-CBC3-SHA and EDH-RSA-DES-CBC3-SHA are maintained for backward compatibility with clients that do not support AES.
  • While the goal is to support a broad range of clients, we reasonably disable a number of ciphers that have little support (such as SEED, CAMELLIA, ...).

Old backward compatibility

This is the old ciphersuite that works with all clients back to Windows XP/IE6. It should be used as a last resort only.

  • Ciphersuites: ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:ECDHE-RSA-DES-CBC3-SHA:ECDHE-ECDSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:DES-CBC3-SHA:HIGH:SEED:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!RSAPSK:!aDH:!aECDH:!EDH-DSS-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA:!SRP
  • Versions: TLSv1.2, TLSv1.1, TLSv1, SSLv3
  • TLS curves: prime256v1, secp384r1, secp521r1
  • Certificate type: RSA
  • Certificate curve: None
  • Certificate signature: sha256WithRSAEncryption
  • RSA key size: 2048
  • DH Parameter size: 1024
  • ECDH Parameter size: 256
  • HSTS: max-age=15768000
  • Certificate switching: sha1WithRSAEncryption
0xCC,0xA9  -  ECDHE-ECDSA-CHACHA20-POLY1305   TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=ChaCha20(256)  Mac=AEAD
0xCC,0xA8  -  ECDHE-RSA-CHACHA20-POLY1305     TLSv1.2  Kx=ECDH  Au=RSA    Enc=ChaCha20(256)  Mac=AEAD
0xC0,0x2F  -  ECDHE-RSA-AES128-GCM-SHA256     TLSv1.2  Kx=ECDH  Au=RSA    Enc=AESGCM(128)    Mac=AEAD
0xC0,0x2B  -  ECDHE-ECDSA-AES128-GCM-SHA256   TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AESGCM(128)    Mac=AEAD
0xC0,0x30  -  ECDHE-RSA-AES256-GCM-SHA384     TLSv1.2  Kx=ECDH  Au=RSA    Enc=AESGCM(256)    Mac=AEAD
0xC0,0x2C  -  ECDHE-ECDSA-AES256-GCM-SHA384   TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AESGCM(256)    Mac=AEAD
0x00,0x9E  -  DHE-RSA-AES128-GCM-SHA256       TLSv1.2  Kx=DH    Au=RSA    Enc=AESGCM(128)    Mac=AEAD
0x00,0xA2  -  DHE-DSS-AES128-GCM-SHA256       TLSv1.2  Kx=DH    Au=DSS    Enc=AESGCM(128)    Mac=AEAD
0x00,0xA3  -  DHE-DSS-AES256-GCM-SHA384       TLSv1.2  Kx=DH    Au=DSS    Enc=AESGCM(256)    Mac=AEAD
0x00,0x9F  -  DHE-RSA-AES256-GCM-SHA384       TLSv1.2  Kx=DH    Au=RSA    Enc=AESGCM(256)    Mac=AEAD
0xC0,0x27  -  ECDHE-RSA-AES128-SHA256         TLSv1.2  Kx=ECDH  Au=RSA    Enc=AES(128)       Mac=SHA256
0xC0,0x23  -  ECDHE-ECDSA-AES128-SHA256       TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AES(128)       Mac=SHA256
0xC0,0x13  -  ECDHE-RSA-AES128-SHA            SSLv3    Kx=ECDH  Au=RSA    Enc=AES(128)       Mac=SHA1
0xC0,0x09  -  ECDHE-ECDSA-AES128-SHA          SSLv3    Kx=ECDH  Au=ECDSA  Enc=AES(128)       Mac=SHA1
0xC0,0x28  -  ECDHE-RSA-AES256-SHA384         TLSv1.2  Kx=ECDH  Au=RSA    Enc=AES(256)       Mac=SHA384
0xC0,0x24  -  ECDHE-ECDSA-AES256-SHA384       TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=AES(256)       Mac=SHA384
0xC0,0x14  -  ECDHE-RSA-AES256-SHA            SSLv3    Kx=ECDH  Au=RSA    Enc=AES(256)       Mac=SHA1
0xC0,0x0A  -  ECDHE-ECDSA-AES256-SHA          SSLv3    Kx=ECDH  Au=ECDSA  Enc=AES(256)       Mac=SHA1
0x00,0x67  -  DHE-RSA-AES128-SHA256           TLSv1.2  Kx=DH    Au=RSA    Enc=AES(128)       Mac=SHA256
0x00,0x33  -  DHE-RSA-AES128-SHA              SSLv3    Kx=DH    Au=RSA    Enc=AES(128)       Mac=SHA1
0x00,0x40  -  DHE-DSS-AES128-SHA256           TLSv1.2  Kx=DH    Au=DSS    Enc=AES(128)       Mac=SHA256
0x00,0x6B  -  DHE-RSA-AES256-SHA256           TLSv1.2  Kx=DH    Au=RSA    Enc=AES(256)       Mac=SHA256
0x00,0x38  -  DHE-DSS-AES256-SHA              SSLv3    Kx=DH    Au=DSS    Enc=AES(256)       Mac=SHA1
0x00,0x39  -  DHE-RSA-AES256-SHA              SSLv3    Kx=DH    Au=RSA    Enc=AES(256)       Mac=SHA1
0xC0,0x12  -  ECDHE-RSA-DES-CBC3-SHA          SSLv3    Kx=ECDH  Au=RSA    Enc=3DES(168)      Mac=SHA1
0xC0,0x08  -  ECDHE-ECDSA-DES-CBC3-SHA        SSLv3    Kx=ECDH  Au=ECDSA  Enc=3DES(168)      Mac=SHA1
0x00,0x16  -  EDH-RSA-DES-CBC3-SHA            SSLv3    Kx=DH    Au=RSA    Enc=3DES(168)      Mac=SHA1
0x00,0x9C  -  AES128-GCM-SHA256               TLSv1.2  Kx=RSA   Au=RSA    Enc=AESGCM(128)    Mac=AEAD
0x00,0x9D  -  AES256-GCM-SHA384               TLSv1.2  Kx=RSA   Au=RSA    Enc=AESGCM(256)    Mac=AEAD
0x00,0x3C  -  AES128-SHA256                   TLSv1.2  Kx=RSA   Au=RSA    Enc=AES(128)       Mac=SHA256
0x00,0x3D  -  AES256-SHA256                   TLSv1.2  Kx=RSA   Au=RSA    Enc=AES(256)       Mac=SHA256
0x00,0x2F  -  AES128-SHA                      SSLv3    Kx=RSA   Au=RSA    Enc=AES(128)       Mac=SHA1
0x00,0x35  -  AES256-SHA                      SSLv3    Kx=RSA   Au=RSA    Enc=AES(256)       Mac=SHA1
0x00,0x6A  -  DHE-DSS-AES256-SHA256           TLSv1.2  Kx=DH    Au=DSS    Enc=AES(256)       Mac=SHA256
0x00,0x32  -  DHE-DSS-AES128-SHA              SSLv3    Kx=DH    Au=DSS    Enc=AES(128)       Mac=SHA1
0x00,0x0A  -  DES-CBC3-SHA                    SSLv3    Kx=RSA   Au=RSA    Enc=3DES(168)      Mac=SHA1
0x00,0x9A  -  DHE-RSA-SEED-SHA                SSLv3    Kx=DH    Au=RSA    Enc=SEED(128)      Mac=SHA1
0x00,0x99  -  DHE-DSS-SEED-SHA                SSLv3    Kx=DH    Au=DSS    Enc=SEED(128)      Mac=SHA1
0xCC,0x15  -  DHE-RSA-CHACHA20-POLY1305       TLSv1.2  Kx=DH    Au=RSA    Enc=ChaCha20(256)  Mac=AEAD
0xC0,0x77  -  ECDHE-RSA-CAMELLIA256-SHA384    TLSv1.2  Kx=ECDH  Au=RSA    Enc=Camellia(256)  Mac=SHA384
0xC0,0x73  -  ECDHE-ECDSA-CAMELLIA256-SHA384  TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=Camellia(256)  Mac=SHA384
0x00,0xC4  -  DHE-RSA-CAMELLIA256-SHA256      TLSv1.2  Kx=DH    Au=RSA    Enc=Camellia(256)  Mac=SHA256
0x00,0xC3  -  DHE-DSS-CAMELLIA256-SHA256      TLSv1.2  Kx=DH    Au=DSS    Enc=Camellia(256)  Mac=SHA256
0x00,0x88  -  DHE-RSA-CAMELLIA256-SHA         SSLv3    Kx=DH    Au=RSA    Enc=Camellia(256)  Mac=SHA1
0x00,0x87  -  DHE-DSS-CAMELLIA256-SHA         SSLv3    Kx=DH    Au=DSS    Enc=Camellia(256)  Mac=SHA1
0x00,0xC0  -  CAMELLIA256-SHA256              TLSv1.2  Kx=RSA   Au=RSA    Enc=Camellia(256)  Mac=SHA256
0x00,0x84  -  CAMELLIA256-SHA                 SSLv3    Kx=RSA   Au=RSA    Enc=Camellia(256)  Mac=SHA1
0xC0,0x76  -  ECDHE-RSA-CAMELLIA128-SHA256    TLSv1.2  Kx=ECDH  Au=RSA    Enc=Camellia(128)  Mac=SHA256
0xC0,0x72  -  ECDHE-ECDSA-CAMELLIA128-SHA256  TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=Camellia(128)  Mac=SHA256
0x00,0xBE  -  DHE-RSA-CAMELLIA128-SHA256      TLSv1.2  Kx=DH    Au=RSA    Enc=Camellia(128)  Mac=SHA256
0x00,0xBD  -  DHE-DSS-CAMELLIA128-SHA256      TLSv1.2  Kx=DH    Au=DSS    Enc=Camellia(128)  Mac=SHA256
0x00,0x45  -  DHE-RSA-CAMELLIA128-SHA         SSLv3    Kx=DH    Au=RSA    Enc=Camellia(128)  Mac=SHA1
0x00,0x44  -  DHE-DSS-CAMELLIA128-SHA         SSLv3    Kx=DH    Au=DSS    Enc=Camellia(128)  Mac=SHA1
0x00,0xBA  -  CAMELLIA128-SHA256              TLSv1.2  Kx=RSA   Au=RSA    Enc=Camellia(128)  Mac=SHA256
0x00,0x41  -  CAMELLIA128-SHA                 SSLv3    Kx=RSA   Au=RSA    Enc=Camellia(128)  Mac=SHA1
0x00,0x96  -  SEED-SHA                        SSLv3    Kx=RSA   Au=RSA    Enc=SEED(128)      Mac=SHA1

Rationale:

  • You should take a hard look at your infrastructure needs before using this configuration; it is intended for special use cases only, and most servers should use the intermediate configuration instead.
  • SSLv3 is enabled to support WinXP SP2 clients on IE.
  • SHA1 certificates are authorized but only via certificate switching, meaning the server must implement custom logic to provide a SHA1 certs to old clients, and SHA256 certs to all others. More information in the "Certificates Switching" section later in this document.
  • Most ciphers that are not clearly broken and dangerous to use are supported

JSON version of the recommendations

You can find the recommendations above in JSON format at the address https://statics.tls.security.mozilla.org/server-side-tls-conf-4.0.json.

This location is permanent and can be referenced in scripts and tools. The file is versioned and will not change, to avoid breaking tools when we update the recommendations.

If you wish to point to the latest version of the recommendations, use this address: [https://statics.tls.security.mozilla.org/server-side-tls-conf.json. Be advised the above will always point to the latest version and will not provide backward compatibility. If you use it to automatically configure your servers without review, it may break things. Prefer the version-specific files instead.

Previous versions

  • None

Mandatory discards

  • aNULL contains non-authenticated Diffie-Hellman key exchanges, that are subject to Man-In-The-Middle (MITM) attacks
  • eNULL contains null-encryption ciphers (cleartext)
  • EXPORT are legacy weak ciphers that were marked as exportable by US law
  • RC4 contains ciphers that use the deprecated ARCFOUR algorithm
  • DES contains ciphers that use the deprecated Data Encryption Standard
  • SSLv2 contains all ciphers that were defined in the old version of the SSL standard, now deprecated
  • MD5 contains all the ciphers that use the deprecated message digest 5 as the hashing algorithm

Forward Secrecy

The concept of forward secrecy is simple: client and server negotiate a key that never hits the wire, and is destroyed at the end of the session. The RSA private from the server is used to sign a Diffie-Hellman key exchange between the client and the server. The pre-master key obtained from the Diffie-Hellman handshake is then used for encryption. Since the pre-master key is specific to a connection between a client and a server, and used only for a limited amount of time, it is called Ephemeral.

With Forward Secrecy, if an attacker gets a hold of the server's private key, it will not be able to decrypt past communications. The private key is only used to sign the DH handshake, which does not reveal the pre-master key. Diffie-Hellman ensures that the pre-master keys never leave the client and the server, and cannot be intercepted by a MITM.

DHE handshake and dhparam

When an ephemeral Diffie-Hellman cipher is used, the server and the client negotiate a pre-master key using the Diffie-Hellman algorithm. This algorithm requires that the server sends the client a prime number and a generator. Neither are confidential, and are sent in clear text. However, they must be signed, such that a MITM cannot hijack the handshake.

As an example, TLS_DHE_RSA_WITH_AES_128_CBC_SHA256 works as follow:

server key exchange message as displayed in Wireshark
client key exchange message as displayed in Wireshark
  1. Server sends Client a SERVER KEY EXCHANGE message during the SSL Handshake. The message contains:
    1. Prime number p
    2. Generator g
    3. Server's Diffie-Hellman public value A = g^X mod p, where X is a private integer chosen by the server at random, and never shared with the client. (note: A is called pubkey in wireshark)
    4. signature S of the above (plus two random values) computed using the Server's private RSA key
  2. Client verifies the signature S
  3. Client sends server a CLIENT KEY EXCHANGE message. The message contains:
    1. Client's Diffie-Hellman public value B = g^Y mod p, where Y is a private integer chosen at random and never shared. (note: B is called pubkey in wireshark)
  4. The Server and the Client can now calculate the pre-master secret using each other's public values:
    1. server calculates PMS = B^X mod p
    2. client calculates PMS = A^Y mod p
  5. Client sends a CHANGE CIPHER SPEC message to the server, and both parties continue the handshake using ENCRYPTED HANDSHAKE MESSAGES

The size of the prime number p constrains the size of the pre-master key PMS, because of the modulo operation. A smaller prime almost means weaker values of A and B, which could leak the secret values X and Y. Thus, the prime p should not be smaller than the size of the RSA private key.

Pre-defined DHE groups

Instead of using pre-configured DH groups, or generating their own with "openssl dhparam", operators should use the pre-defined DH groups ffdhe2048, ffdhe3072 or ffdhe4096 recommended by the IETF in [RFC 7919 https://tools.ietf.org/html/rfc7919]. These groups are audited and may be more resistant to attacks than ones randomly generated.

Note: if you must support old Java clients, Dh groups larger than 1024 bits may block connectivity (see #DHE_and_Java).

ffdhe2048

-----BEGIN DH PARAMETERS-----
MIIBCAKCAQEA//////////+t+FRYortKmq/cViAnPTzx2LnFg84tNpWp4TZBFGQz
+8yTnc4kmz75fS/jY2MMddj2gbICrsRhetPfHtXV/WVhJDP1H18GbtCFY2VVPe0a
87VXE15/V8k1mE8McODmi3fipona8+/och3xWKE2rec1MKzKT0g6eXq8CrGCsyT7
YdEIqUuyyOP7uWrat2DX9GgdT0Kj3jlN9K5W7edjcrsZCwenyO4KbXCeAvzhzffi
7MA0BM0oNC9hkXL+nOmFg/+OTxIy7vKBg8P+OxtMb61zO7X8vC7CIAXFjvGDfRaD
ssbzSibBsu/6iGtCOGEoXJf//////////wIBAg==
-----END DH PARAMETERS-----

ffdhe3072

-----BEGIN DH PARAMETERS-----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-----END DH PARAMETERS-----

ffdhe4096

-----BEGIN DH PARAMETERS-----
MIICCAKCAgEA//////////+t+FRYortKmq/cViAnPTzx2LnFg84tNpWp4TZBFGQz
+8yTnc4kmz75fS/jY2MMddj2gbICrsRhetPfHtXV/WVhJDP1H18GbtCFY2VVPe0a
87VXE15/V8k1mE8McODmi3fipona8+/och3xWKE2rec1MKzKT0g6eXq8CrGCsyT7
YdEIqUuyyOP7uWrat2DX9GgdT0Kj3jlN9K5W7edjcrsZCwenyO4KbXCeAvzhzffi
7MA0BM0oNC9hkXL+nOmFg/+OTxIy7vKBg8P+OxtMb61zO7X8vC7CIAXFjvGDfRaD
ssbzSibBsu/6iGtCOGEfz9zeNVs7ZRkDW7w09N75nAI4YbRvydbmyQd62R0mkff3
7lmMsPrBhtkcrv4TCYUTknC0EwyTvEN5RPT9RFLi103TZPLiHnH1S/9croKrnJ32
nuhtK8UiNjoNq8Uhl5sN6todv5pC1cRITgq80Gv6U93vPBsg7j/VnXwl5B0rZp4e
8W5vUsMWTfT7eTDp5OWIV7asfV9C1p9tGHdjzx1VA0AEh/VbpX4xzHpxNciG77Qx
iu1qHgEtnmgyqQdgCpGBMMRtx3j5ca0AOAkpmaMzy4t6Gh25PXFAADwqTs6p+Y0K
zAqCkc3OyX3Pjsm1Wn+IpGtNtahR9EGC4caKAH5eZV9q//////////8CAQI=
-----END DH PARAMETERS-----

DHE and ECDHE support

Most modern clients that support both ECDHE and DHE typically prefer the former, because ECDHE provides faster handshakes than DHE ([1], [2]).

Unfortunately, some widely used clients lack support for ECDHE and must then rely on DHE to provide perfect forward secrecy:

  • Android < 3.0.0
  • Java < 7
  • OpenSSL < 1.0.0

Note that schannel on Windows XP technically support DHE, but only with DSA keys, making it unusable on the internet in practice.

DHE and Java

Java 6 and 7 do not support Diffie-Hellman parameters larger than 1024 bits. If your server expects to receive connections from java 6 clients and wants to enable PFS, it must provide a DHE parameter of 1024 bits.

If keeping the compatibility with Java < 7 is a necessity, thus preventing the use of large DH keys, three solutions are available:

  • using custom 1024-bit DH parameters, different from Oakley group 2, preferably generated with openssl dhparam 1024 ;
  • if the software used does not support custom DH parameters, like Apache HTTPd < 2.2.30, it is possible to keep using the 1024-bit DH Oakley group 2, knowing these clients may be at risk of a compromise;
  • it is also possible to completely disable DHE. This means that clients not supporting ECDHE will be reverting to static RSA, giving up Forward Secrecy.

The case of Java 7 is a bit different. Java 7 supports ECDHE ciphers, so if the server provides ECDHE and prioritizes it before DHE ciphers using server side ordering, then Java 7 will use ECDHE and not care about the size of the DHE parameter. In this situation, the server can use 2048 bits DHE parameters for all other clients.

However, if the server does not support ECDHE, then Java 7 will use DHE and fail if the parameter is larger than 1024 bits. When failing, the handshake will not attempt to fall back to the next cipher in line, but simply fail with the error "java.lang.RuntimeException: Could not generate DH keypair".

Java supported ECDHE prioritized smallest DH parameter size
6 irrelevant 1024
7 NO 1024
7 YES 2048
8 irrelevant 2048


OCSP Stapling

When connecting to a server, clients should verify the validity of the server certificate using either a Certificate Revocation List (CRL), or an Online Certificate Status Protocol (OCSP) record. The problem with CRL is that the lists have grown huge and takes forever to download.

OCSP is much more lightweight, as only one record is retrieved at a time. But the side effect is that OCSP requests must be made to a 3rd party OCSP responder when connecting to a server, which adds latency and potential failures. In fact, the OCSP responders operated by CAs are often so unreliable that browser will fail silently if no response is received in a timely manner. This reduces security, by allowing an attacker to DoS an OCSP responder to disable the validation.

The solution is to allow the server to send its cached OCSP record during the TLS handshake, therefore bypassing the OCSP responder. This mechanism saves a roundtrip between the client and the OCSP responder, and is called OCSP Stapling.

The server will send a cached OCSP response only if the client requests it, by announcing support for the status_request TLS extension in its CLIENT HELLO.

OCSP Stapling.png

Most servers will cache OCSP response for up to 48 hours. At regular intervals, the server will connect to the OCSP responder of the CA to retrieve a fresh OCSP record. The location of the OCSP responder is taken from the Authority Information Access field of the signed certificate. For example, with StartSSL:

Authority Information Access:
      OCSP - URI:http://ocsp.startssl.com/sub/class1/server/ca

Support for OCSP Stapling can be tested using the -status option of the OpenSSL client.

$ openssl s_client -connect monitor.mozillalabs.com:443 -status
...
======================================
OCSP Response Data:
    OCSP Response Status: successful (0x0)
    Response Type: Basic OCSP Response
    Version: 1 (0x0)
...

Session Resumption

Session Resumption is the ability to reuse the session secrets previously negotiated between a client and a server for a new TLS connection. This feature greatly increases the speed establishment of TLS connections after the first handshake, and is very useful for connections that use Perfect Forward Secrecy with a slow handshake like DHE.

Session Resumption can be performed using one of two methods:

  1. session identifier: When establishing a first session, the server generates an arbitrary session ID sent to the client. On subsequent connections, the client sends the session ID in the CLIENT HELLO message, indicating to the server it wants to reuse an existing state. If the server can find a corresponding state in its local cache, it reuse the session secrets and skips directly to exchanging encrypted data with the client. If the cache stored on the server is compromised, session keys from the cache can be used to decrypt past and future sessions.
  2. session tickets: Storing a cache on the server might be problematic for systems that handle very large numbers of clients. Session tickets provide an alternative where the server sends the encrypted state (ticket) to the client instead of storing it in its local cache. The client can send back the encrypted state to the server in subsequent connections, thus allowing session resumption. This method requires symmetric keys on the server to encrypt and decrypt session tickets. If the keys are compromised, an attacker obtains access to session keys and can decrypt past and future sessions.

Session resumption is a very useful performance feature of TLS, but also carries a significant amount of risk. Most servers do not purge sessions or ticket keys, thus increasing the risk that a server compromise would leak data from previous (and future) connections.

The current recommendation for web servers is to enable session resumption and benefit from the performance improvement, but to restart servers daily when possible. This ensure that sessions get purged and ticket keys get renewed on a regular basis.

HSTS: HTTP Strict Transport Security

HSTS is a HTTP header sent by a server to a client, indicating that the current site must only be accessed over HTTPS until expiration of the HSTS value is reached.

The header format is very simple, composed only of a max-age parameter that indicates when the directive should expire. max-age is expressed in seconds. A typical value is 15768000 seconds, or 6 months.

Strict-Transport-Security: max-age=15768000

HSTS is becoming more and more of a standard, but should only be used when the site's operators are confident that HTTPS will be available continuously for the duration of max-age. Once the HSTS header is sent to client, HTTPS cannot be disabled on the site until the last client has expired its HSTS record.

HPKP: Public Key Pinning Extension for HTTP

See RFC7469.

HPKP is an experimental HTTP header sent by a server to a client, to indicate that some certificates related to the site should be pinned in the client. The client would thus refuse to establish a connection to the server if the pining does not comply.

Due to its experimental nature, HPKP is currently not recommended on production sites. More informations can be found on the MDN description page.

Certificates Switching

Certificates Switching is a technique by which a server provides a different X.509 certificate to a client based on specific selection criteria. This technique is used primarily to maintain backward compatibility with very old clients, such as Internet Explorer 6 on Windows XP SP2.

On XPSP2, IE6 is only able to establish connections to servers that provide a certificate signed with sha1WithRSAEncryption. Those certificates are not issued by modern CAs anymore, and all sites have been encouraged to upgrade to SHA-256 certificates. As modern browsers gradually block connections backed by SHA-1 certificates, sites that need to maintain compatibility with XPSP2 must implement certificates switching to provide a SHA-1 cert to old clients and a SHA-256 cert to modern ones.

Certificate switching can be implemented in various ways. A simplistic approach is to select the certificate based on the protocol version (SHA-256 to TLS clients, SHA-1 to SSLv3 ones). A more sophisticated approach consists at looking inside the CLIENT HELLO for SHA-256 support in the "signature_algorithms" extension.

Few servers currently support cert switching. It is possible to implement it using HAProxy, and vendors like Cloudflare propose it in their offering.

Recommended Server Configurations

All configuration samples have been moved to the configuration generator and the Security/TLS_Configurations archive. Access the generator by clicking the image below:

Server-side-tls-config-generator.png

Tools

CipherScan

See https://github.com/jvehent/cipherscan

Cipherscan is a small Bash script that connects to a target and list the preferred Ciphers. It's an easy way to test a web server for available ciphers, PFS key size, elliptic curves, support for OCSP Stapling, TLS ticket lifetime and certificate trust.

$ ./cipherscan jve.linuxwall.info
..........................
prio  ciphersuite                  protocols              pfs_keysize
1     ECDHE-RSA-AES128-GCM-SHA256  TLSv1.2                ECDH,P-256,256bits
2     ECDHE-RSA-AES256-GCM-SHA384  TLSv1.2                ECDH,P-256,256bits
3     DHE-RSA-AES256-GCM-SHA384    TLSv1.2                DH,4096bits
4     DHE-RSA-AES128-GCM-SHA256    TLSv1.2                DH,4096bits
5     ECDHE-RSA-AES128-SHA256      TLSv1.2                ECDH,P-256,256bits
6     ECDHE-RSA-AES128-SHA         TLSv1,TLSv1.1,TLSv1.2  ECDH,P-256,256bits
7     ECDHE-RSA-AES256-SHA384      TLSv1.2                ECDH,P-256,256bits
8     ECDHE-RSA-AES256-SHA         TLSv1,TLSv1.1,TLSv1.2  ECDH,P-256,256bits
9     DHE-RSA-AES128-SHA256        TLSv1.2                DH,4096bits
10    DHE-RSA-AES128-SHA           TLSv1,TLSv1.1,TLSv1.2  DH,4096bits
11    DHE-RSA-AES256-SHA256        TLSv1.2                DH,4096bits
12    AES128-GCM-SHA256            TLSv1.2
13    AES256-GCM-SHA384            TLSv1.2
14    ECDHE-RSA-DES-CBC3-SHA       TLSv1,TLSv1.1,TLSv1.2  ECDH,P-256,256bits
15    EDH-RSA-DES-CBC3-SHA         TLSv1,TLSv1.1,TLSv1.2  DH,4096bits
16    DES-CBC3-SHA                 TLSv1,TLSv1.1,TLSv1.2
17    DHE-RSA-AES256-SHA           TLSv1,TLSv1.1,TLSv1.2  DH,4096bits
18    DHE-RSA-CAMELLIA256-SHA      TLSv1,TLSv1.1,TLSv1.2  DH,4096bits
19    AES256-SHA256                TLSv1.2
20    AES256-SHA                   TLSv1,TLSv1.1,TLSv1.2
21    CAMELLIA256-SHA              TLSv1,TLSv1.1,TLSv1.2
22    DHE-RSA-CAMELLIA128-SHA      TLSv1,TLSv1.1,TLSv1.2  DH,4096bits
23    AES128-SHA256                TLSv1.2
24    AES128-SHA                   TLSv1,TLSv1.1,TLSv1.2
25    CAMELLIA128-SHA              TLSv1,TLSv1.1,TLSv1.2

Certificate: trusted, 2048 bit, sha1WithRSAEncryption signature
TLS ticket lifetime hint: 300
OCSP stapling: supported

SSL Labs (Qualys)

Available here: https://www.ssllabs.com/ssltest/

Qualys SSL Labs provides a comprehensive SSL testing suite.

GlobalSign has a modified interface of SSL Labs that is interesting as well: https://sslcheck.globalsign.com/

Attacks on SSL and TLS

BEAST (CVE-2011-3389)

Beast is a vulnerability in the Initialization Vector (IV) of the CBC mode of AES, Camellia and a few other ciphers that use CBC mode. The attack allows a MITM attacker to recover plaintext values by encrypting the same message multiple times.

BEAST is mitigated in TLS1.1 and above.

more: https://blog.torproject.org/blog/tor-and-beast-ssl-attack

LUCKY13

Lucky13 is another attack on CBC mode that listen for padding checks to decrypt ciphertext.

more: https://www.imperialviolet.org/2013/02/04/luckythirteen.html

RC4 weaknesses

As of February 2015, the IETF explicitely prohibits the use of RC4: RFC 7465.

It has been proven that RC4 biases in the first 256 bytes of a cipherstream can be used to recover encrypted text. If the same data is encrypted a very large number of times, then an attacker can apply statistical analysis to the results and recover the encrypted text. While hard to perform, this attack shows that it is time to remove RC4 from the list of trusted ciphers.

In a public discussion (bug 927045), it has been recommended to replace RC4 with 3DES. This would impact Internet Explorer 7 and 8 users that, depending on the OS, do not support AES, and will negotiate only RC4 or 3DES ciphers. Internet Explorer uses the cryptographic library “schannel”, which is OS dependent. schannel supports AES in Windows Vista, but not in Windows XP.

While 3DES provides more resistant cryptography, it is also 30 times slower and more cpu intensive than RC4. For large web infrastructure, the CPU cost of replacing RC4 with 3DES is non-zero. For this reason, we recommend that administrators evaluate their traffic patterns, and make the decision of replacing RC4 with 3DES on a per-case basis. At Mozilla, we evaluated that the impact on CPU usage is minor, and thus decided to replace RC4 with 3DES where backward compatibility is required.

The root cause of the problem is information leakage that occurs when data is compressed prior to encryption. If someone can repeatedly inject and mix arbitrary content with some sensitive and relatively predictable data, and observe the resulting encrypted stream, then he will be able to extract the unknown data from it.

more: https://community.qualys.com/blogs/securitylabs/2012/09/14/crime-information-leakage-attack-against-ssltls

BREACH

This is a more complex attack than CRIME, which does not require TLS-level compression (it still needs HTTP-level compression).

In order to be successful, it requires to:

  1. Be served from a server that uses HTTP-level compression
  2. Reflect user-input in HTTP response bodies
  3. Reflect a secret (such as a CSRF token) in HTTP response bodies

more: http://breachattack.com/

POODLE (CVE-2014-3566)

POODLE is an attack on the padding used by SSLv3. It is a significant improvement of the BEAST attack which led the cryptography community to recommend disabling SSLv3 globally.

If you can arrange the message to be the correct length then the last block is 15 arbitrary bytes and the padding length (15). Then you arrange an interesting byte to be in the last position of a different block and duplicate that block to the end. If the record is accepted, then you know what the last byte contained because it decrypted to 15. Thus the attacker needs to be able to control some of the plaintext in order to align things in the messages and needs to be able to burn lots of connections (256 per byte, roughly). Thus a secret needs to be repeated in connection after connection (i.e. a cookie).

source: Adam Langley in https://bugzilla.mozilla.org/show_bug.cgi?id=1076983#c29

Daniel Stenberg (Mozilla, cUrl) has a good description of the exploitability of POODLE in http://daniel.haxx.se/blog/2014/10/17/curl-is-no-poodle/

Our guidelines maintain support for SSLv3 in the Old configuration only. This is required for clients on Windows XP service pack 1 & 2 that do not have support for TLSv1.0. Internet Explorer and Chrome on those platforms are impacted. Mozilla wants to be reachable from very old clients, to allow them to download a better browser. Therefore, we maintain SSLv3 compatibility on a limited number of sites. But all sites that do not need that level of compatibility are encouraged to implement the Intermediate configuration

Logjam attack on weak Diffie-Hellman

The Logjam attack describes methods of attacking TLS servers supporting DHE export ciphers, and with weak (<= 1024 bit) Diffie Hellman groups. Modern TLS must use DH parameters of 2048 bits and above, or only use ECDHE. The modern configuration in this guide provide configurations that are not impacted by this issue. The intermediate and old configurations are impacted, and administrators are encourage to use DH parameters of 2048 bits wherever possible.

more: https://weakdh.org

SSL and TLS Settings

SPDY

(see also http://en.wikipedia.org/wiki/SPDY and http://www.chromium.org/spdy/spdy-protocol)

SPDY is a protocol that incorporate TLS, which attempts to reduce latency when loading pages. It is currently not an HTTP standard (albeit it is being drafted for HTTP 2.0), but is widely supported.

SPDY version 3 is vulnerable to the CRIME attack (see also http://zoompf.com/2012/09/explaining-the-crime-weakness-in-spdy-and-ssl) - this is due to the use of compression. Clients currently implement a non-standard hack in with gzip in order to circumvent the vulnerability. SPDY version 4 is planned to include a proper fix.

TLS tickets (RFC 5077)

Once a TLS handshake has been negotiated between the server and the client, both may exchange a session ticket, which contains the session and is usually encrypted with AES-CBC 128bit. This AES key is generally static and only regenerated when the web server is restarted (with recent versions of Apache, it's stored in a file and also kept upon restarts).

The key that encrypts TLS tickets in servers is very hard to manage and potentially introduces a security risk if not renewed regularly: if a server is breached, the key can be stolen and used to decrypt recorded TLS tickets, thus leaking session keys. TLS tickets do bring a performance benefit because of session resumption, but administrators that are more concerned about security than performance may want to disable them entirely. The trade-off we recommend is to implement restarts of web servers and force deletion of local caches to renew encryption keys.

more information: https://media.blackhat.com/us-13/US-13-Daigniere-TLS-Secrets-Slides.pdf

Cipher suites

Different libraries support different cipher suites and refer to them by different names. Mozilla maintains a list of all known cipher suites and their corresponding names.

GnuTLS ciphersuite

Unlike OpenSSL, GnuTLS will panic if you give it ciphers aren't supported by the library. That makes it very difficult to share a default ciphersuite to use in GnuTLS. The next best thing is using the following ciphersuite, and removing the components that break on your own version:

NONE:+VERS-TLS1.2:+VERS-TLS1.1:+VERS-TLS1.0:+ECDHE-RSA:+DHE-RSA:+RSA:+AES-128-GCM:+AES-128-CBC:+AES-256-CBC:+SIGN-RSA-SHA256:+SIGN-RSA-SHA384:+SIGN-RSA-SHA512:+SIGN-RSA-SHA224:+SIGN-RSA-SHA1:+SIGN-DSA-SHA256:+SIGN-DSA-SHA224:+SIGN-DSA-SHA1:+CURVE-ALL:+AEAD:+SHA256:+SHA384:+SHA1:+COMP-NULL

A ciphersuite can be tested in GnuTLS using gnutls-cli.

$ gnutls-cli --version
gnutls-cli 3.1.26

$ gnutls-cli -l --priority NONE:+VERS-TLS1.2:+VERS-TLS1.1:+VERS-TLS1.0:+ECDHE-RSA:+DHE-RSA:+RSA:+AES-128-GCM:+AES-128-CBC:+AES-256-CBC:+SIGN-RSA-SHA256:+SIGN-RSA-SHA384:+SIGN-RSA-SHA512:+SIGN-RSA-SHA224:+SIGN-RSA-SHA1:+SIGN-DSA-SHA256:+SIGN-DSA-SHA224:+SIGN-DSA-SHA1:+CURVE-ALL:+AEAD:+SHA256:+SHA384:+SHA1:+COMP-NULL
Cipher suites for NONE:+VERS-TLS1.2:+VERS-TLS1.1:+VERS-TLS1.0:+ECDHE-RSA:+DHE-RSA:+RSA:+AES-128-GCM:+AES-128-CBC:+AES-256-CBC:+SIGN-RSA-SHA256:+SIGN-RSA-SHA384:+SIGN-RSA-SHA512:+SIGN-RSA-SHA224:+SIGN-RSA-SHA1:+SIGN-DSA-SHA256:+SIGN-DSA-SHA224:+SIGN-DSA-SHA1:+CURVE-ALL:+AEAD:+SHA256:+SHA384:+SHA1:+COMP-NULL
TLS_ECDHE_RSA_AES_128_GCM_SHA256                    0xc0, 0x2f  TLS1.2
TLS_ECDHE_RSA_AES_128_CBC_SHA256                    0xc0, 0x27  TLS1.0
TLS_ECDHE_RSA_AES_128_CBC_SHA1                      0xc0, 0x13  SSL3.0
TLS_ECDHE_RSA_AES_256_CBC_SHA1                      0xc0, 0x14  SSL3.0
TLS_DHE_RSA_AES_128_GCM_SHA256                      0x00, 0x9e  TLS1.2
TLS_DHE_RSA_AES_128_CBC_SHA256                      0x00, 0x67  TLS1.0
TLS_DHE_RSA_AES_128_CBC_SHA1                        0x00, 0x33  SSL3.0
TLS_DHE_RSA_AES_256_CBC_SHA256                      0x00, 0x6b  TLS1.0
TLS_DHE_RSA_AES_256_CBC_SHA1                        0x00, 0x39  SSL3.0
TLS_RSA_AES_128_GCM_SHA256                          0x00, 0x9c  TLS1.2
TLS_RSA_AES_128_CBC_SHA256                          0x00, 0x3c  TLS1.0
TLS_RSA_AES_128_CBC_SHA1                            0x00, 0x2f  SSL3.0
TLS_RSA_AES_256_CBC_SHA256                          0x00, 0x3d  TLS1.0
TLS_RSA_AES_256_CBC_SHA1                            0x00, 0x35  SSL3.0

Certificate types: none
Protocols: VERS-TLS1.2, VERS-TLS1.1, VERS-TLS1.0
Compression: COMP-NULL
Elliptic curves: CURVE-SECP256R1, CURVE-SECP384R1, CURVE-SECP521R1
PK-signatures: SIGN-RSA-SHA256, SIGN-RSA-SHA384, SIGN-RSA-SHA512, SIGN-RSA-SHA224, SIGN-RSA-SHA1, SIGN-DSA-SHA256, SIGN-DSA-SHA224, SIGN-DSA-SHA1

A good way to debug the ciphersuite is by performing a test connection. If the ciphersuite isn't supported, gnutls-cli will stop reading it at the component that is causing the issue.

$ gnutls-cli --debug 9999 google.com --priority 'NONE:+VERS-TLS1.2:+VERS-TLS1.1:+VERS-TLS1.0:+ECDHE-RSA:+DHE-RSA:+RSA:+AES-128-GCM:+AES-128-CBC:+AES-256-CBC:+SIGN-RSA-SHA256:+SIGN-RSA-SHA384:+SIGN-RSA-SHA512:+SIGN-RSA-SHA224:+SIGN-RSA-SHA1:+SIGN-DSA-SHA256:+SIGN-DSA-SHA224:+SIGN-DSA-SHA1:+CURVE-ALL:+AEAD:+SHA256:+SHA384:+SHA1:+COMP-NULL'
|<2>| ASSERT: gnutls_priority.c:812
Syntax error at: +SIGN-RSA-SHA224:+SIGN-RSA-SHA1:+SIGN-DSA-SHA256:+SIGN-DSA-SHA224:+SIGN-DSA-SHA1:+SHA256:+SHA384:+SHA1:+COMP-NULL

In the example above, the component SIGN-RSA-SHA224 is not supported by this version of gnutls and should be removed from the ciphersuite.

Version History

Version Editor Changes
4.2 April King Updated cipher suite table
4.1 Julien Vehent Clarify Logjam notes, Clarify risk of TLS Tickets
4 Julien Vehent Recommend ECDSA in modern level, remove DSS ciphers, publish configurations as JSON
3.8 Julien Vehent redo cipher names chart (April King), move version chart (April King), update Intermediate cipher suite (ulfr)
3.7 Julien Vehent cleanup version table (April King), add F5 conf samples (warburtron), add notes about DHE (rgacogne)
3.6 Julien Vehent bump intermediate DHE to 2048, add note about java compatibility
3.5 alm comment on weakdh vulnerability
3.4 Julien Vehent added note about session resumption, HSTS, and HPKP
3.3 Julien Vehent fix SHA256 prio, add POODLE details, update various templates
3.2 Julien Vehent Added intermediate compatibility mode, renamed other modes
3.1 Julien Vehent Added non-backward compatible ciphersuite
3 Julien Vehent Remove RC4 for 3DES, fix ordering in openssl 0.9.8 (1024430), various minor updates
2.5.1 Julien Vehent Revisit ELB capabilities
2.5 Julien Vehent Update ZLB information for OCSP Stapling and ciphersuite
2.4 Julien Vehent Moved a couple of aes128 above aes256 in the ciphersuite
2.3 Julien Vehent Precisions on IE 7/8 AES support (thanks to Dobin Rutishauser)
2.2 Julien Vehent Added IANA/OpenSSL/GnuTLS correspondence table and conversion tool
2.1 Julien Vehent RC4 vs 3DES discussion. r=joes r=tinfoil
2.0 Julien Vehent, kang Public release.
1.5 Julien Vehent, kang added details for PFS DHE handshake, added nginx configuration details; added Apache recommended conf
1.4 Julien Vehent revised ciphersuite. Prefer AES before RC4. Prefer 128 before 256. Prefer DHE before non-DHE.
1.3 Julien Vehent added netscaler example conf
1.2 Julien Vehent ciphersuite update, bump DHE-AESGCM above ECDH-RC4
1.1 Julien Vehent, kang integrated review comments from Infra; SPDY information
1.0 Julien Vehent creation
 
Document Status: READY