ISMA Encryption & Authentication (ISMACryp)

An Internet Streaming Media Alliance (ISMA) specification covering "content encryption, message authentication (integrity) services, an RTP payload format and a file format for pre-encrypted content for ISMA 1.0, ISMA 2.0 and more generally any media that can be stored as elementary stream in an ISO media file [14496-12." The official name of the specification is "ISMA Encryption and Authentication" but it is unofficially (commonly) called "ISMACryp", a term used throughout the specification.

ISMACryp protocol for Wireshark relates only to the content encryption part in terms of header analysis (no decryption of encrypted payloads).


Nov. 2007 - ISMACryp 2.0 published, providing codec agnostic encryption.

Oct. 2006 - ISMACryp 1.1 released, providing support for the encryption of H.264/AVC video and HE-AAC audio for RTP transport and storage in MPEG-4 files.

Protocol dependencies

  • RTP: For streaming, ISMACryp uses RTP as its transport protocol.

  • SDP: ISMACryp uses SDP to set parameters. This is not currently supported so parameters have to be set manually via preferences.

Example traffic

XXX - Add example decoded traffic for this protocol here (as plain text or Wireshark screenshot).


The ISMACryp dissector is fully functional for analysis of ISMACryp 2.0 & 1.1 RTP streams. However, no decryption is done, only interpretation of ISMACryp headers / parameters. Currently ISMACryp configuration parameters are set via preferences as support for SDP (typically provided via SAP) is not provided.

TODO - enable automatic setup of ISMACryp parameters via SDP,if present. Currently values are set manually via preferences.

Preference Settings

There are some ISMACryp_Preferences.

Example capture file

The following capture file contains ISMACryp protected audio and video streams. SDP information for RTP and ISMACryp can be found via SAP/SDP.

Display Filter

A complete list of ISMACryp display filter fields can be found in the display filter reference

Show only the ISMACryp based traffic:


You can isolate different RTP streams (e.g. audio / video) via RTP payload type &/or the UDP port used.

Show only the ISMACryp traffic over UDP port XXX:

 ismacryp && udp.port==XXX 

Show only the ISMACryp traffic for RTP dynamic payload type 96:

 ismacryp && rtp.p_type==96 

Capture Filter

You cannot directly filter ISMACryp protocol while capturing, but you can, for example, filter a given UDP port YYY:

 udp port YYY 

External links


Imported from on 2020-08-11 23:15:24 UTC