This article contains information on Cipher Suites, detailing the algorithms used for securing network connections via TLS / SSL, and lists various cipher groups with their respective strengths and configurations, along with supported key exchange methods, elliptic curves, and signature algorithms.
A Cipher Suite is a set of algorithms that secure a network connection using Transport Layer Security (TLS) or Secure Socket Layer (SSL). Each set of algorithms usually contains:
- Key exchange algorithm: This is used to exchange a key between two devices and encrypt / decrypt messages sent between them.
- Bulk encryption algorithm: This is used to encrypt the data being sent.
- Message Authentication Code (MAC) algorithm: This provides data integrity checks to ensure the data sent doesn't change in transit.
Cipher Suites can also include signatures and an authentication algorithm to help authenticate the server and/or client (including SMTP submission). There are many Cipher Suites containing different combinations of these algorithms.
Cipher Suites
Some Cipher Suites offer better security than others. The list below of the ciphers Mimecast may use, depending on your configuration, is ordered from strongest (top) to weakest (bottom). If a Cipher group has multiple ciphers, the first in the group is chosen first.
You won't have all the Cipher groups enabled; this depends on the functionality enabled on your Account. For example, Ciphers in the gcmPFSCiphers group are stronger than those in the phsCiphergroup. However, as gcmPFSCiphers is optional, the strongest Cipher by default is TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA.
tls1.3Ciphers
Unlike TLS 1.2, these do not encode key exchange or authentication in the cipher name. Those are negotiated separately, via supported groups and signature algorithm extensions. These ciphers are preferred when TLS 1.3 is negotiated.
| Cipher | Enabled | Optional | Comments |
|
TLS_AES_256_GCM_SHA384 TLS_AES_128_GCM_SHA256 |
Yes | No | TLS 1.3 Cipher Suites. |
|
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256 |
No | Yes | These ciphers could be enabled depending on your account's functionality. |
|
TLS_AES_128_CCM_SHA256 TLS_AES_128_CCM_8_SHA256 |
No | No | Not supported. |
gcmPFSCiphers
| Ciphers | Enabled | Optional | Comments |
|
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 TLS_DHE_DSS_WITH_AES_128_GCM_SHA256 TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 TLS_DHE_DSS_WITH_AES_256_GCM_SHA384 |
No | Yes | These ciphers could be enabled depending on your account's functionality. |
pfsCiphers
| Ciphers | Enabled | Optional | Comments |
|
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA |
Yes | No | |
|
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256 |
No | No | Supported in the underlying implementation but not exposed through the cipher selector configuration. |
gcmVeryStrongCiphers
| Ciphers | Enabled | Optional | Comments |
|
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 TLS_DHE_DSS_WITH_AES_128_GCM_SHA256 TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 TLS_DHE_DSS_WITH_AES_256_GCM_SHA384 TLS_ECDH_ECDSA_WITH_AES_128_GCM_SHA256 TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384 TLS_ECDH_RSA_WITH_AES_128_GCM_SHA256 TLS_ECDH_RSA_WITH_AES_256_GCM_SHA384 |
No | Yes | These ciphers could be enabled depending on your account's functionality. |
veryStrongCiphers
| Ciphers | Enabled | Optional | Comments |
|
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 TLS_DHE_DSS_WITH_AES_256_CBC_SHA256 TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA384 TLS_ECDH_RSA_WITH_AES_256_CBC_SHA384 TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256 TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 TLS_DHE_RSA_WITH_AES_128_CBC_SHA256 TLS_DHE_DSS_WITH_AES_128_CBC_SHA256 TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA256 TLS_ECDH_RSA_WITH_AES_128_CBC_SHA256 TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA TLS_DHE_RSA_WITH_AES_256_CBC_SHA TLS_DHE_DSS_WITH_AES_256_CBC_SHA TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA TLS_ECDH_RSA_WITH_AES_256_CBC_SHA TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA TLS_DHE_RSA_WITH_AES_128_CBC_SHA TLS_DHE_DSS_WITH_AES_128_CBC_SHA TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA TLS_ECDH_RSA_WITH_AES_128_CBC_SHA TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA TLS_ECDH_ECDSA_WITH_3DES_EDE_CBC_SHA TLS_ECDH_RSA_WITH_3DES_EDE_CBC_SHA |
Yes | No |
gcmStrongCiphers
| Ciphers | Enabled | Optional | Comments |
|
TLS_RSA_WITH_AES_128_GCM_SHA256 TLS_RSA_WITH_AES_256_GCM_SHA384 |
No | Yes | These ciphers could be enabled depending on your account's functionality. |
strongCiphers
| Ciphers | Enabled | Optional | Comments |
|
TLS_RSA_WITH_AES_256_CBC_SHA TLS_RSA_WITH_AES_128_CBC_SHA SSL_RSA_WITH_3DES_EDE_CBC_SHA |
Yes | No |
mediumCiphers
| Ciphers | Enabled | Optional | Comments |
|
SSL_DHE_RSA_WITH_3DES_EDE_CBC_SHA SSL_DHE_DSS_WITH_3DES_EDE_CBC_SHA |
No | Yes | These ciphers could be enabled in compatibility mode. |
beastMitigationCiphers
| Ciphers | Enabled | Optional | Comments |
|
SSL_RSA_WITH_RC4_128_SHA SSL_RSA_WITH_RC4_128_MD5 |
No | Yes | These ciphers could be enabled in compatibility mode. |
weakCiphers
| Ciphers | Enabled | Optional | Comments |
|
SSL_DHE_RSA_WITH_DES_CBC_SHA SSL_DHE_DSS_WITH_DES_CBC_SHA SSL_RSA_WITH_DES_CBC_SHA SSL_RSA_EXPORT_WITH_RC4_40_MD5 SSL_RSA_EXPORT_WITH_DES40_CBC_SHA SSL_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA SSL_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA |
No | Yes | These ciphers could be enabled in compatibility mode. |
anonCiphers
| Ciphers | Enabled | Optional | Comments |
|
TLS_ECDH_anon_WITH_AES_256_CBC_SHA TLS_ECDH_anon_WITH_AES_128_CBC_SHA TLS_ECDH_anon_WITH_RC4_128_SHA TLS_ECDH_anon_WITH_3DES_EDE_CBC_SHA TLS_DH_anon_WITH_AES_256_CBC_SHA TLS_DH_anon_WITH_AES_128_CBC_SHA SSL_DH_anon_WITH_3DES_EDE_CBC_SHA SSL_DH_anon_WITH_RC4_128_MD5 SSL_DH_anon_WITH_DES_CBC_SHA SSL_DH_anon_EXPORT_WITH_RC4_40_MD5 SSL_DH_anon_EXPORT_WITH_DES40_CBC_SHA |
No | Yes | These ciphers could be enabled depending on your account's configuration. |
renegotiationCiphers
| Ciphers | Enabled | Optional | Comments |
| TLS_EMPTY_RENEGOTIATION_INFO_SCSV | Yes | No |
Supported Key Exchange Methods
The following key exchange methods are supported. In TLS 1.3, key exchange is decoupled from the cipher suite and negotiated via the supported_groups extension.
| Method | Supported | Comments |
| psk_dhe_ke | Yes | PSK with DHE key exchange, used in TLS 1.3 session resumption. |
Supported Elliptic Curves
The following named elliptic curves are supported for ECDHE key exchange and ECDSA authentication in both TLS 1.2 and TLS 1.3.
| Curve | Supported | Comments |
| secp256r1 (P-256) | Yes | 256-bit prime curve. Widely supported and recommended. |
| secp384r1 (P-384) | Yes | 384-bit prime curve. Required for NCSC compliance configurations. |
Supported Signature Algorithms
The following signature algorithms are supported for certificate authentication. In TLS 1.3 these are negotiated separately from the cipher suite.
RSA-PSS (RSAE), for use with RSA certificates.
| Algorithm | Supported | Comments |
| rsa_pss_rsae_sha256 | Yes | RSA-PSS signature with SHA-256. |
| rsa_pss_rsae_sha384 | Yes | RSA-PSS signature with SHA-384. |
| rsa_pss_rsae_sha512 | Yes | RSA-PSS signature with SHA-512. |
RSA-PSS (PSS) for Use with PSS Certificates
| Algorithm | Supported | Comments |
| rsa_pss_pss_sha256 | Yes | RSA-PSS signature with SHA-256. |
| rsa_pss_pss_sha384 | Yes | RSA-PSS signature with SHA-384. |
| rsa_pss_pss_sha512 | Yes | RSA-PSS signature with SHA-512. |
ECDSA
| Algorithm | Supported | Comments |
| ecdsa_secp256r1_sha256 | Yes | ECDSA with P-256 curve and SHA-256. |
| ecdsa_secp384r1_sha384 | Yes | ECDSA with P-384 curve and SHA-384. |
National Cyber Security Centre Ciphers (UK Government Compliance)
| Ciphers | Enabled | Optional | Comments |
|
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 TLS_DHE_DSS_WITH_AES_256_GCM_SHA384 TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 TLS_DHE_RSA_WITH_AES_128_CBC_SHA256 |
Yes | No | These ciphers conform to the Securing Government Email guidance issued by the National Cyber Security Centre (NCSC). |
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