Audio/Video streams encryption in Office Communicator Version 1.0
I have some questions about Audio/Video encryption in Office Communicator Version 1.0 and hope that someone can give me some idea.
For two OC, if we want to encrypt the audio/video RTP traffic, the encryption key is sent over the SIP signaling channel. If encryption is required for audio/video streams, something like:
k=base64:PlUeTaTiRmnMNdXkxwpSkjy4UvQkUwZGUxqLLrdK60I
a=encryption:required
will appear in the media description part of the SDP in the SIP message.
It is said that OC version 1.0 uses DES CBC at 56bits. The k= field contains an auto-generated pass phrase. The real key is generated by following the string to key mapping algorithm specified in RFC1890.
Now here comes my questions:
1, Is this a RTP sending key or a receiving key?
2. What is the meaning of "base64:" part in the k= field? Is the part after "base64:" the passphrase itself, or we need to decode it to binary data? Do we need to transform the passphrase to a canonical form before applying the hash algorithm(If the part after "base64:" in the key field is the passphrase, I assume that I just need convert all letters to lower case, but if I need decode that part to binary data, I am not sure how to transform the binary data to a canonical form.)
I tried to figure those questions out through some testing program written by myself, but failed.
Hope that any expert on Office Communicator can give me some advice!
Thanks in advance!
Vicky
