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.

Contents

Recommended configurations

Mozilla SSL Configuration Generator
The Mozilla SSL Configuration Generator
Mozilla maintains three 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
  • Old: Services accessed by very old clients or libraries, such as Internet Explorer 8 (Windows XP), Java 6, or OpenSSL 0.9.8
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 27 4.4.2 31 12 11 (Win7) 8u31 1.0.1 20 9
Old 1 2.3 1 12 8 (WinXP) 6 0.9.8 5 1

The ordering of cipher suites in the Old configuration is very important, as it determines the priority with which algorithms are selected.

OpenSSL will ignore cipher suites it doesn't understand, so always use the full set of cipher suites below, in their recommended order. The use of the Old configuration with modern versions of OpenSSL may require custom builds with support for deprecated ciphers.


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: X25519, prime256v1, secp384r1
  • HSTS: max-age=63072000 (two years)
  • Maximum 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 negligable 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:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384
  • Protocols: TLS 1.2, TLS 1.3
  • TLS curves: 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)
  • Maximum certificate lifespan: 90 days (recommended) to 2 years
  • 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
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
  • 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
    • 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
    • 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

Old backward compatibility

This configuration is compatible with a number of very old clients, and should be used only as a last resort.

  • Cipher suites (TLS 1.3): TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256
  • Cipher suites (TLS 1.0 - 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:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:DHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES256-SHA256:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA
  • Protocols: TLS 1.0, TLS 1.1, TLS 1.2, TLS 1.3
  • TLS curves: X25519, prime256v1, secp384r1
  • Certificate type: RSA (2048-bits)
  • Certificate curve: None
  • DH parameter size: 1024 (generated with openssl dhparam 1024)
  • HSTS: max-age=63072000 (two years)
  • Maximum certificate lifespan: 90 days (recommended) to 2 years
  • Cipher preference: server 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
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
0xCC,0xAA  -  DHE-RSA-CHACHA20-POLY1305      TLSv1.2  Kx=DH    Au=RSA    Enc=CHACHA20/POLY1305(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         TLSv1    Kx=ECDH  Au=ECDSA  Enc=AES(128)                Mac=SHA1
0xC0,0x13  -  ECDHE-RSA-AES128-SHA           TLSv1    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
0xC0,0x28  -  ECDHE-RSA-AES256-SHA384        TLSv1.2  Kx=ECDH  Au=RSA    Enc=AES(256)                Mac=SHA384
0xC0,0x0A  -  ECDHE-ECDSA-AES256-SHA         TLSv1    Kx=ECDH  Au=ECDSA  Enc=AES(256)                Mac=SHA1
0xC0,0x14  -  ECDHE-RSA-AES256-SHA           TLSv1    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
0x00,0x6B  -  DHE-RSA-AES256-SHA256          TLSv1.2  Kx=DH    Au=RSA    Enc=AES(256)                Mac=SHA256
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:
    • Take a hard look at your infrastructure needs before using this configuration; it is intended for special use cases only
    • If possible, use this configuration only for endpoints that require it, segregating it from other traffic
    • SSLv3 has been disabled entirely, ending support for older Windows XP SP2 clients. Users requiring support for Windows XP SP2 may use previous versions of this configuration, with the caveat that SSLv3 is no longer safe to use
    • This configuration requires custom builds to work with modern versions of OpenSSL, using enable-ssl3, enable-ssl3-method, enable-deprecated, and enable-weak-ssl-ciphers
    • Most ciphers that are not clearly broken and dangerous to use are supported

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
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