[cryptography] The NSA and secure VoIP

John Case case at SDF.ORG
Thu Mar 1 23:22:33 EST 2012


On Thu, 1 Mar 2012, Jeffrey Walton wrote:

> On Thu, Mar 1, 2012 at 10:27 PM, Steven Bellovin <smb at cs.columbia.edu> wrote:
>> http://www.scmagazine.com.au/News/292189,nsa-builds-android-phone-for-top-secret-calls.aspx
>> makes for interesting reading.  I was particularly intrigued by this:
>>
>>        Voice calls are encrypted twice in accordance with NSA policy,
>>        using IPSEC and SRTP, meaning a failure requires “two independent
>>        bad things to happen,” Salter said.
>>
>> Margaret Salter is the head of the Information Assurance Directorate
>> of the NSA.
> Interesting. I seem to recall that cascading ciphers is frowned upon
> on sci.crypt. I wonder if this is mis-information....


Yes, I've had that beaten into my head from books/talks/posts forever now, 
but I never quite understood it.

If the end result of your ciphertext has headers or metadata that can be 
used for known-plaintext attack, then it makes sense, but if you are just 
feeding raw ciphertext into the next algorithm, it shouldn't be a 
danger... right ?


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