Add XChaChaPoly cipher

[Frando]

This adds the XChaChaPoly cipher to snow. The crypto used is the chacha20poly1305 crate, which also has a dependency on the aead crate. I added a simple test that follows the ChaChaPoly test. Likely more tests are needed.

I notices that XChaChaPoly is missing when trying to handshake with a hypercore-protocol stream from nodejs

[mcginty]

Rad! Thanks for taking this on. I'd love to get this merged in.

Because XChaChaPoly isn't in the official Noise specification, I'm thinking this should be behind a feature gate. Thoughts?

[Frando]

This makes sense, I added a feature gate.

[Frando]

I rebased this on master and simplified the implementation similar to the ChaChaPoly cipher after the move to the aead crate.

[mcginty]

The code looks good, thanks for updating it!

Before merging this, we need to update ci-tests.sh since xchachapoly is not a default feature but we want to test it regardless.

When enabling the feature a la:

 set -e
 TARGET="$([ -n "$1" ] && echo "--target $1" || echo "")"

+COMMON_FEATURES="xchachapoly vector-tests"
 set -x
 cargo check --benches
 cargo test $TARGET --no-default-features
-cargo test $TARGET --features "vector-tests"
-cargo test $TARGET --features "ring-resolver vector-tests"
-cargo test $TARGET --features "ring-accelerated vector-tests"
-cargo test $TARGET --features "hfs pqclean_kyber1024 vector-tests"
-cargo test $TARGET --features "ring-resolver hfs pqclean_kyber1024 vector-tests"
-cargo test $TARGET --features "libsodium-resolver vector-tests"
-cargo test $TARGET --features "libsodium-accelerated vector-tests"
+cargo test $TARGET --features "$COMMON_FEATURES"
+cargo test $TARGET --features "ring-resolver $COMMON_FEATURES"
+cargo test $TARGET --features "ring-accelerated $COMMON_FEATURES"
+cargo test $TARGET --features "hfs pqclean_kyber1024 $COMMON_FEATURES"
+cargo test $TARGET --features "ring-resolver hfs pqclean_kyber1024 $COMMON_FEATURES"
+cargo test $TARGET --features "libsodium-resolver $COMMON_FEATURES"
+cargo test $TARGET --features "libsodium-accelerated $COMMON_FEATURES"

we'll see some tests fail when other resolvers are enabled, so we'll have to fix those before pushing.

[Frando]

Right, I added the feature to CI tests and updated the ring resolver to not crash.

[Frando]

Hei, can this be merged now that the CI changes are done?

[mcginty]

Sorry for the delay and thanks for rebasing. Merged :).

[cryptoquick]

Does this close #71 ?

[Frando]

Yes, it does! There's been no release though since it has been merged.