Opportunistic SRTP Support in VoIP Devices

The widely used VoIP signalling protocol SIP has a bad reputation. In my opinion it's mostly unwarranted. If you don't stray too far off piste and have a decent NAT traversal behaviour things will generally work fine.

In the ideal world everything would be encrypted, but there's a plethora of end of life and unsupported devices out there, and devices which may support encryption are often configured by end users that may not enable it.

Enter Opportunistic SRTP - a method of encrypting the audio stream if it's supported by the other end, and it's not supported just fall back to plain old RTP

Photo by Markus Spiske on Unsplash

Factory Reseting a Polycom VVX 450

I recently acquired a Polycom VVX 450 off Ebay for £30, which is an absolute bargain for a modern 12 Line SIP phone with OPUS / SILK support. 

There was some risk however, it had previously been used by a VoIP provider that shares its name with a character in the Greek Alphabet and some providers lockdown the configuration to make it challenging to make them work with another provider.

Getting around these locks can occasionally involve intercepting traffic and redirecting it to your own TFTP or HTTP server, however with this phone it didn't seem to be the case.