0bf87476f5 test: add ChaCha20 test triggering 32-bit block counter overflow (Sebastian Falbesoner)
7f2a985147 tests: improve ChaCha20 unit tests (Pieter Wuille)
511a8d406e crypto: Implement RFC8439-compatible variant of ChaCha20 (Pieter Wuille)
Pull request description:
Based on and replaces part of #25361, part of the BIP324 project (#27634). See also #19225 for background.
There are two variants of ChaCha20 in use. The currently implemented one uses a 64-bit nonce and a 64-bit block counter, while the one used in RFC8439 (and thus BIP324) uses a 96-bit nonce and 32-bit block counter. This PR changes the logic to use the 96-bit nonce variant, though in a way that's compatible with >256 GiB output (by automatically incrementing the first 32-bit part of the nonce when the block counter overflows).
For those who reviewed the original PR, the biggest change is here that the 96-bit nonce is passed as a Nonce96 type (pair of 32-bit + 64-bit integer) rather than a 12-byte array.
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