Hi Everyone,

We added the IETF's version of ChaCha named ChaChaTLS. It is slightly 
different than Bernstein's original version. The IETF's version of ChaCha 
is specified in https://tools.ietf.org/html/rfc7539.

ChaChaTLS is mostly the same as Bernstein's algorithm. A few of the 
differences are:

  1. 256-bit key only
  2. 20-rounds only
  3. 12-byte nonce
  4. 1-word block counter
  5. Initial block counter can be specified

We may want to backport Initial Block Counter back to Bernstein's ChaCha. 
It looks useful to me, and it can be done without breaking ChaCha ABI.

There's a couple of open questions we are sorting out, and there may be 
some minor changes in the future. For example, we are not sure how to 
handle block counter wrap at the moment. At the moment we wrap and assert 
in Debug builds. We also disabled the SIMD implementation until we can get 
some independent test vectors that exercise large blocks.

The wiki page with the documentation and sample code is available at 
https://www.cryptopp.com/wiki/ChaChaTLS.

Jeff


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