[Cryptech Tech] Incremental digest outputs

[Peter Gutmann]

Rob Austein <sra at hactrn.net> writes:

>but we don't support doing things like:
>
>  context = SHAxxxInit()
>  context.addData(foo)
>  result1 = context.finalize()
>  context.addData(bar)
>  result2 = context.finalize()

The only protocol AFAIK that requires this is TLS, due to design brokenness
that leads to nondeterministic handshakes.  Since few hash implementations
support this type of operation, I run two parallel hash contexts (ugh) and use
whatever one I need to finalise the hashing at a given point.  I believe that
other implementations do this, or something similar, too.

In other words there shouldn't be any need to support this type of operation.

Peter.