Encryption for Skype for Business Server 2015

Skype for Business Server 2015 uses TLS and MTLS to encrypt instant messages. All server-to-server traffic requires MTLS, regardless of whether the traffic is confined to the internal network or crosses the internal network perimeter. When connecting Skype for Business Server 2015 to 3rd party IPPBX systems or SIP trunks TLS is optional but strongly recommended between the Mediation Server and media gateway. If TLS is configured on this link, MTLS is required. Therefore, the gateway must be configured with a certificate from a CA that is trusted by the Mediation Server.

Note

A security advisory regarding SSL 3.0 was published in 2014. Disabling SSL 3.0 in Skype for Business Server 2015 is a supported option. To learn more about the security advisory, see Disabling SSL 3.0 in Lync Server 2013 and Skype for Business Server 2015.

[!SECURITY NOTE] To ensure the strongest cryptographic protocol is used, Skype for Business Server 2015 will offer TLS encryption protocols in the following order to clients: TLS 1.2 , TLS 1.1, TLS 1.0. TLS is a critical aspect of Skype for Business Server 2015 and thus it is required in order to maintain a supported environment.

The following table summarizes the protocol requirements for each type of traffic.

Traffic Protection

Traffic type Protected by
Server-to-server
MTLS
Client-to-server
TLS
Instant messaging and presence
TLS
Audio and video and desktop sharing of media
SRTP
Desktop sharing (signaling)
TLS
Web conferencing
TLS
Meeting content download, address book download, distribution group expansion
HTTPS

Media Encryption

Media traffic is encrypted using Secure RTP (SRTP), a profile of Real-Time Transport Protocol (RTP) that provides confidentiality, authentication, and replay attack protection to RTP traffic. In addition, media flowing in both directions between the Mediation Server and its internal next hop is also encrypted using SRTP. Media flowing in both directions between the Mediation Server and a media gateway is optionally encrypted and recommended. The Mediation Server can support encryption to the media gateway, but the gateway must support MTLS and storage of a certificate.

Note

If you are implementing a hybrid environment, you must also modify the Skype for Business Server 2015 encryption level. By default, the encryption level is Required. You must change this setting to Supported by using the Skype for Business Server Management Shell. For more information about setting up hybrid, see Move users from Skype for Business Online to on premises in the Deployment documentation.

FIPS

Skype for Business Server 2015 and Microsoft Exchange Server 2016 operate with support for Federal Information Processing Standard (FIPS) 140-2 algorithms if the Windows Server operating systems are configured to use the FIPS 140-2 algorithms for system cryptography. To implement FIPS support, you must configure each server running Skype for Business Server 2015 to support it.