Enhancing SSL Security

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The default configuration of most operating systems allow any set of supported ciphers and hashes to be used by applications when acting as SSL client or server. While this ensures full compatibility with other client and server applications, it does no longer match the expectation in SSL encrypted communication in regards to privacy and trust due to supporting insecure protocols, cipher suites and hash algorithms.

Therefore enhancing the security of SSL mainly consists of disabling these insecure protocols, ciphers and hashes as well as prioritize cipher suites that allow the usage of Perfect Forward Secrecy.

As MailStore Server relies on Windows' security support provider (SSP) called Secure Channel (also known as Schannel), a number of registry keys have to be created or modified in order to disable insecure protocols, ciphers and hashes. Although Microsoft's Technet article How to restrict the use of certain cryptographic algorithms and protocols in Schannel.dll describes in detail which registry keys affect the security provider settings, it is not recommended to manually change these keys. A safer way to adjust the Schannel settings for server applications is Nartac Software's IIS Crypto tool.

Important note: Modifying the configuration of the security support provider (SSP) in Windows may affect general operating system functions such as authentication services and remote desktop and management capabilities or other third party applications that rely on SSP. Thus careful testing of all services is required after applying the changes.

Recommended Settings

Highest level of security can be achieved with the following settings in IIS Crypto on the MailStore Server computer.

Protocols Enabled TLS 1.0
TLS 1.1
TLS 1.2
Ciphers Enabled AES 128/128
AES 256/256
Hashes Enabled SHA

SHA256
SHA384
SHA512

Key Exchange Enabled Diffie-Hellman

PKCS
ECDH

SSL Cipher Suite Order TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P521

TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P384
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P256
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA_P521
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA_P384
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA_P256
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P521
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P384
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA_P521
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA_P384
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA_P256
TLS_RSA_WITH_AES_256_GCM_SHA384*
TLS_RSA_WITH_AES_128_GCM_SHA256*
TLS_RSA_WITH_AES_256_CBC_SHA256
TLS_RSA_WITH_AES_256_CBC_SHA
TLS_RSA_WITH_AES_128_CBC_SHA256
TLS_RSA_WITH_AES_128_CBC_SHA
TLS_RSA_WITH_3DES_EDE_CBC_SHA

*Only in Windows 2012 R2 and above

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  • MailStore Server is one of the leading email archiving solutions for SMB.
  • For private use there is a free tool for email archiving furthermore: MailStore Home.