[cryptography] "stream MAC" - does anything like it exist?

travis+ml-rbcryptography at subspacefield.org travis+ml-rbcryptography at subspacefield.org
Tue Sep 14 19:35:44 EDT 2010

On Wed, Sep 15, 2010 at 04:51:35AM +1200, Peter Gutmann wrote:
> It would help if the OP could indicate how much CPU budget they had available
> for encryption and/or authentication, just the two chapters referenced above
> contain ~120 references for different mechanisms and tradeoffs.

I was just driving to work one day and wondering, "suppose you were an
important public official who recorded all his activities, and you
were trying to assure the public that a voluntarily-disclosed portion
of a (e.g. sound) recording had not been tampered with; how would you
do it?"

Obviously tacking a 16-byte HMAC (or worse, digsig) to each 16-bit
sample wouldn't be very space-efficient.

In practice, I suppose you could just sign every second, and only
disclose with one second granularity.

Same principles may apply with videoconferencing, or perhaps IM.

The idea of efficiency also could matter with, say, an interactive TCP
session (e.g. keystrokes in SSH on TCP with Nagle algorithm), but I
think you really want those fully authenticated, because a rogue
keystroke could be, well, really bad (rm -fr /^Jtmp/bar).  I don't
think there's any clever solution to be found there, but it seems a
shame to spend 56 octets overhead (TCP~=40, HMAC=16) for 1 octet of
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