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Polycom®, Inc. 155
Implementing Media Encryption for
Secured Conferencing
Encryption is available at the conference and participant levels, based on AES 128 (Advanced Encryption
Standard) and is fully H.233/H.234 compliant and the Encryption Key exchange DH 1024-bit
(Diffie-Hellman) standards.
Media Encryption Guidelines
● Encryption is not available in all countries and it is enabled in the MCU license. Contact Polycom
Support to enable it.
● Media encryption is supported in CP, SVC Only and mixed CP and SVC Conferencing Modes.
● Endpoints must support both AES 128 encryption and DH 1024 key exchange standards which are
compliant with H.235 (H.323) to encrypt and to join an encrypted conference.
● The encryption mode of the endpoints is not automatically recognized, therefore the encryption mode
must be set for the conference or the participants (when defined).
● Media Encryption for ISDN/PSTN participants is not supported in cascaded conferences.
● Conference level encryption must be set in the Profile, and cannot be changed once the conference
is running.
● If an endpoint connected to an encrypted conference stops encrypting its media, it is disconnected
from the conference.
● In Cascaded conferences, the link between the cascaded conferences must be encrypted in order to
encrypt the conferences.
● The recording link can be encrypted when recording from an encrypted conference to the
RealPresence Capture Server or RSSsystem that is set to encryption. For more information, see Dial
Out Recording Link Encryption.
● Encryption of SIP Media is supported using SRTP (Secured Real-time Transport Protocol) and the
AES key exchange method.
● Encryption of SIP Media requires the encryption of SIP signaling - TLS Transport Layer must be used.
● Encryption of SIP Media is supported in conferences as follows:
All media channels are encrypted: video, audio and FECC.
Collaboration Server SRTP implementation complies with Microsoft SRTP implementation.
LPR is not supported with SRTP.
The ENABLE_SIRENLPR_SIP_ENCRYPTION System Flag enables the SirenLPR audio
algorithm when using encryption with the SIP protocol. The default value of this flag is NO
meaning SirenLPR is disabled by default for SIP participants in an encrypted conference. To
enable SirenLPR the System Flag must be added to system.cfg and its value set to YES.
The SEND_SRTP_MKI System Flag enables or disables the inclusion of the MKI field in SRTP
packets sent by the Collaboration Server. The default value of the flag is YES.
Add the flag to system.cfg and set its value set to NO to disable the inclusion of the MKI field in SRTP
packets sent by the Collaboration Server when using endpoints that cannot decrypt SRTP-based
audio and video streams if the MKI (Master Key Identifier) field is included in SRTP packets sent by