[WIP] 64-bit counters for legacy and XChaCha variants, fix looping counter regressions #399
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This is still WIP. So far it is basically a PoC of what is needed to perform these changes.
The overall checklist before merging is:
IetfChaCha20traitsso that there is an explicit representation of a looped/saturated counter. Currently the implementation of StreamCipherCoreWrapper does not allow me to directly implement a cipher that stops once it would loop; in the current implementation I get around this by effectively using a 64-bit counter for the 32-bit counter mode, which allows me to distinguish between a just-initialized cipher (block_pos = 0, pos = 64) and a looped cipher (block_pos = 2**32, pos = 64). Note that this does not currently allow correct behavior at the end of a 64-bit-counter keystream.Ietfvariant to use a 32-bit counter again, fixing thebad_overflow_check{6,7}seek-focused testsSeekNum::from_block_byteintraitsto match the looped counter representation, thereby fixing cipher: Seeking near the end of the keystream causestry_current_posto return an error traits#1808. (NOTE: the test in that issue is present in this PR, and succeeds; that is because I use a 64-bit overall counter even in 32-bitIetfmode)This would close #334, #391.