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Security/Server Side TLS

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The goal of this document is to help operational teams with the configuration of TLS. All Mozilla websites and deployments should follow the recommendations below.

Mozilla maintains this document as a reference guide for navigating the TLS landscape, as well as a configuration generator to assist system administrators. Changes are reviewed and merged by the Mozilla Operations Security and Enterprise Information Security teams.

Updates to this page should be submitted to the server-side-tls repository on GitHub. Issues related to the configuration generator are maintained in their own GitHub repository.

In the interests of usability and maintainability, these guidelines have been considerably simplified from the previous guidelines.

Recommended configurations

 
The Mozilla SSL Configuration Generator Mozilla maintains two recommended configurations for servers using TLS. Pick the correct configuration depending on your audience:

  • Modern: Modern clients that support TLS 1.3, with no need for backwards compatibility
  • Intermediate: Recommended configuration for a general-purpose server
Configuration Firefox Android Chrome Edge Internet Explorer Java OpenSSL Opera Safari
Modern 63 10.0 70 75 -- 11 1.1.1 57 12.1
Intermediate 31.3.0 4.4.2 49 15 (Win10) 11 (Win10) 8u161 1.0.1l 20 9

OpenSSL will ignore cipher suites it doesn't understand, so always use the full set of cipher suites below in their recommended order.

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.


Modern compatibility

For services with clients that support TLS 1.3 and don't need backward compatibility, the Modern configuration provides an extremely high level of security.

  • Cipher suites (TLS 1.3): TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256
  • Cipher suites (TLS 1.2): (none)
  • Protocols: TLS 1.3
  • Certificate type: ECDSA (P-256)
  • TLS curves: X25519MLKEM768, X25519, prime256v1, secp384r1
  • HSTS: max-age=63072000 (two years)
  • Certificate lifespan: 90 days
  • Cipher preference: client chooses
0x13,0x01  -  TLS_AES_128_GCM_SHA256        TLSv1.3  Kx=any  Au=any  Enc=AESGCM(128)             Mac=AEAD
0x13,0x02  -  TLS_AES_256_GCM_SHA384        TLSv1.3  Kx=any  Au=any  Enc=AESGCM(256)             Mac=AEAD
0x13,0x03  -  TLS_CHACHA20_POLY1305_SHA256  TLSv1.3  Kx=any  Au=any  Enc=CHACHA20/POLY1305(256)  Mac=AEAD
  • Rationale:
    • All cipher suites are forward secret and authenticated
    • The cipher suites are all strong and so we allow the client to choose, as they will know best if they have support for hardware-accelerated AES
    • We recommend ECDSA certificates using P-256, as P-384 provides negligible improvements to security and Ed25519 is not yet widely supported

Intermediate compatibility (recommended)

For services that don't need compatibility with legacy clients such as Windows XP or old versions of OpenSSL. This is the recommended configuration for the vast majority of services, as it is highly secure and compatible with nearly every client released in the last five (or more) years.

  • Cipher suites (TLS 1.3): TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256
  • Cipher suites (TLS 1.2): ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305
  • Protocols: TLS 1.2, TLS 1.3
  • TLS curves: X25519MLKEM768, X25519, prime256v1, secp384r1
  • Certificate type: ECDSA (P-256) (recommended), or RSA (2048 bits)
  • DH parameter size: 2048 (ffdhe2048, RFC 7919)
  • HSTS: max-age=63072000 (two years)
  • Certificate lifespan: 90 days (recommended) to 366 days
  • Cipher preference: client chooses
0x13,0x01  -  TLS_AES_128_GCM_SHA256         TLSv1.3  Kx=any   Au=any    Enc=AESGCM(128)             Mac=AEAD
0x13,0x02  -  TLS_AES_256_GCM_SHA384         TLSv1.3  Kx=any   Au=any    Enc=AESGCM(256)             Mac=AEAD
0x13,0x03  -  TLS_CHACHA20_POLY1305_SHA256   TLSv1.3  Kx=any   Au=any    Enc=CHACHA20/POLY1305(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
0xCC,0xA9  -  ECDHE-ECDSA-CHACHA20-POLY1305  TLSv1.2  Kx=ECDH  Au=ECDSA  Enc=CHACHA20/POLY1305(256)  Mac=AEAD
0xCC,0xA8  -  ECDHE-RSA-CHACHA20-POLY1305    TLSv1.2  Kx=ECDH  Au=RSA    Enc=CHACHA20/POLY1305(256)  Mac=AEAD
  • Rationale:
    • All cipher suites are forward secret and authenticated
    • TLS 1.2 is the minimum supported protocol, as recommended by RFC 7525, PCI DSS, and others
    • ECDSA certificates are recommended over RSA certificates, as they allow the use of ECDHE with Windows 7 clients using Internet Explorer 11, as well as allow connections from IE11 on Windows Server 2008 R2
    • The cipher suites are all strong and so we allow the client to choose, as they will know best if they have support for hardware-accelerated AES
    • Windows XP (including all embedded versions) are no longer supported by Microsoft, eliminating the need for many older protocols and ciphers
    • DHE-RSA-* ciphers DHE-RSA-AES128-GCM-SHA256, DHE-RSA-AES256-GCM-SHA384, and DHE-RSA-CHACHA20-POLY1305 are excluded due to being more computationally expensive than ECDHE, and being more vulnerable to resource exhaustion attacks such as the D(HE)at attack (CVE-2002-20001). DHE-RSA-* ciphers were previously included to support limitations of IE11 on Windows 7.
    • Administrators needing to provide access to IE 11 on Windows Server 2008 R2 and who are unable to switch to or add ECDSA certificates can add TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
    • While the goal is to support a broad range of clients, we reasonably disable a number of ciphers that have little support (such as ARIA, Camellia, 3DES, and SEED)
    • 90 days is the recommended maximum certificate lifespan, to encourage certificate issuance automation

JSON version of the recommendations

Mozilla also maintains these recommendations in JSON format, for automated system configuration. This location is versioned and permanent, and can be referenced in scripts and tools. The file will not change, to avoid breaking tools when we update the recommendations.

We also maintain a rolling version of these recommendations, with the caveat that they may change without warning and without providing backwards compatibility. As it may break things if you use it to automatically configure your servers without review, we recommend you use the version-specific file instead.

Version History

Version Editor Changes
6.0 Glenn Strauss Remove Old configuration
5.8 Glenn Strauss Remove kDHE ciphers from Intermediate and Old 
 Change Old dhParamSize from 1024 to 2048
 Change Old to use ffdhe2048 instead of locally generated dhparams
 Prepend X25519MLKEM768 PQC hybrid KEM to recommended groups
5.7 Gene Wood Add DHE-RSA-CHACHA20-POLY1305 cipher to the Intermediate configuration
5.6 April King Fixed incorrect cipher ordering for the Intermediate configuration
5.5 April King Update certificate lifespan to reflect browser policy changes
5.3 April King Bump links to point to 5.3 guidelines, since it fixes a small JSON error
5.0.1 April King Add note about IE 11 on Windows Server 2008 R2
5.0 April King Server Side TLS 5.0
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
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