Re: [Linphone-developers] Set Master Key for SRTP in linphone

[Greg Troxel]

Dmitry Alexandrov <dag@gnui.org> writes:

> Greg Troxel <gdt@lexort.com> wrote:
>> Dmitry Alexandrov <dag@gnui.org> writes:
>>
>>>> When people and programs simply say "SRTP", I think they could mean either 
>>>> of these:
>>>>   Session Description Protocol (SDP) Security Descriptions for Media 
>>>> Streams https://tools.ietf.org/html/rfc4568 SRTP Extension for DTLS 
>>>> https://tools.ietf.org/html/rfc5764
>>>
>>> Any example of the latter?
>>
>> I don't know if people really use DTLS-SRTP.
>
> Yes, this is what people mostly use.  Not with SIP, though, but with WebRTC.

I see - that makes sense.  But I was thinking SIP, with linphone.

>>> They could rather mean SRTP proper.
>>
>> I don't follow "SRTP proper".  If you mean "just SRTP without a key 
>> management protocol"
>
> Yes, just SRTP by itself.  Whatʼs wrong with it?  You can decompose it even 
> further and refer to just RTP and just AES, cannot you?

Sure, you can talk about decomposition.  But we are talking about a UI
button labeled SRTP that does not have a key management option or a
manual key option.

>> then this requires a UI at each end to input the same key
>
> No, this usually requires some another protocol for key negotiation.

But then that isn't 'just SRTP'.  It's SRTP with Key Manaegment Protocol
X, which usually has a name like SDES-SRTP or ZRTP.

I have never seen anything do SRTP where users are expected to enter
keys manually.  So the choice is about the key management protocol,
which needs to be specified.