[OTR-dev] Extra symmetric key in Java implementations

Ian Goldberg ian at cypherpunks.ca
Thu Aug 16 08:30:27 EDT 2012

On Wed, Aug 15, 2012 at 11:44:19PM -0700, Tommy C. Li wrote:
> Hi,
> I wasn't able to find the referenced
> otrl_message_symkey
> function in the C library either. Has it been removed since 2008?

Look in version 4 of libotr; that's where it is.

> Is there any difference in the "extra" symmetric key compared to just generating 256 random bits and sending it to the counterparty inside a TLV?

Yes.  In the "extra" symkey model, the value is derived from the current
DH parameters.  That way, both sides are assured it's fresh.

   - Ian

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