Decode websocket MessagePack (Fiddler Everywhere)

[Yoni]

How can I decode a MessagePack of a certain websocket  ?

I tried to convert the hex to base64 then use an online msgpack converter to json but it didn't work.

I'm using Fiddler Everywhere.

(Attached an image)

Thank you !

[Nick Iliev]

Hello Yoni,

 

A Websocket message can contain a string or binary data (see example for both below)

While you can use Fiddler to decrypt string messages (base64) automatically, this is not true for binary data. Binary data is intended to provide additional encryption, compression (or both), and optimized data transfer. Fiddler can't automatically decode binary data—it can only be done through reverse engineering or by having the information needed to create a decryption algorithm.

As mentioned above, Fiddler can only decode WebSocket frames marked as text frames, but it won't decode frames marked as binary. When working with binary data, you can extract it through the HEX inspector and use it for further inspection.

 

Regards,
Nick Iliev
Progress Telerik

[Yoni]

Thank you for the response !

how can I find more information about the decryption algorithm ? maybe through the handshake ?

[Nick Iliev]

The information for the decryption is not necessarily available in the HTTP session - it depends on the specific implementation of the client and server applications.

Note that Fiddler Everywhere can handle and decrypt some MessagePack messages using a known algorithm - for example, with Fiddler Everywhere, you can decrypt messages made through SignalR.what