sha3: have ShakeHash extend hash.Hash

Package sha3 recommends the SHAKE functions for new uses, but this is
currently somewhat inconvenient because ShakeHash does not implement
hash.Hash. This is understandable, as SHAKE supports arbitrary-length
outputs whereas hash.Hash only supports fixed-length outputs. But
there's a natural fixed-length output to provide: the minimum output
that still provides SHAKE's full-strength generic security.

While here, tweak Sum so that its temporary buffer can be stack
allocated.

Also, tweak the panic message in Write so that the error text is more
readily understandable to Go programmers without needing to be
familiar with crypto jargon, and add a similar check in Sum.

Change-Id: Icf037d3990a71de5630f8825606614443f8c5245
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/526937
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Adam Langley <agl@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>

0 files changed, 0 insertions, 0 deletions