SIGMA-I Key Exchange (#378)

* Move `KeGroup` to `KeyExchange::Group`

- Introduce `KeyExchange::Hash`, which separates the OPRF hash from the one used in `KeyExchange`.
- Remove `De/Serialize` requirement on key exchange messages and states, which forced a lot of where bounds on downstream users.
- Rename `KeGroup` to `Group`.
- Replace `D` generic for hash with `H`.

* Use `voprf::derive_key()` directly

* Implement SIGMA-I key exchange

* Improve `KeyExchange` for SIGMA-I and Ed25519

* Implement EdDSA

* Un-qualify some method calls

* SIGMA-I: only include client identity in client mac

* SIGMA-I: include server mac in client signature

* Expose key exchange types in `crate` & move modules

* Implement Ed25519ph

* Document `ed25519` crate feature

* Remove `ristretto255-voprf` crate feature

* Adjust CI crate feature testing

* Fix Rustdoc

* Remove unnecessary generic parameters from SIGMA-I

* Properly mark to-do's with TODO

* Assorted fixes

* SIGMA-I: include context in signature

* SIGMA-I: include identifiers in signature

* Merge `ServerLoginStart/FinishParameters`

* Re-export more necessary types

* More carefully expose types

* Add ECDSA test

* SIGMA-I: share context hashing

* De-duplicate client static public key storage

* Hide `KeyExchange` better

* Use the correct hash in the root documentation

* Bump `derive-where`

* Format documentation examples a bit further

* Add remote OPRF seed documentation

* Rename `deserialize_key_pair` to `deserialize_take_key_pair`

* Add more key tests

* Remove `SharedSecret` trait

* SIGMA-I refactor message API

* Share more implementation between 3DH and SIGMA-I

* Remove unnecessary zero scalar check for Curve25519

* Use correct hash in test

* Add some more TODOs

* Exclude `tests` folder from Cargo publishing

* Enable missing dependencies

* Use right crate for testing Ed25519

* Remove unnecessary `Sized` constraints

* Remove unnecessary `ecdsa` crate features

* Move signature de/serialization to trait methods

* Nit: move import to appropriate location

* Add warning to SIGMA-I

.github/workflows/main.yml

@@ -13,10 +13,12 @@ jobs:
       fail-fast: false
       matrix:
         backend_feature:
-          - --features ristretto255-voprf
           -
-          - --features curve25519,ristretto255-voprf
+          - --features ristretto255
           - --features curve25519
+          - --features ecdsa
+          - --features ed25519
+          - --features ristretto255,curve25519,ecdsa,ed25519
         frontend_feature:
           -
           - --features argon2
@@ -69,10 +71,12 @@ jobs:
           # 32-bit x86
           - i686-unknown-linux-gnu
         backend_feature:
-          - --features ristretto255-voprf
           -
-          - curve25519,ristretto255-voprf
-          - curve25519
+          - --features ristretto255
+          - --features curve25519
+          - --features ecdsa
+          - --features ed25519
+          - --features ristretto255,curve25519,ecdsa,ed25519
     steps:
       - uses: actions/checkout@main
       - uses: hecrj/setup-rust-action@v2
@@ -140,10 +144,12 @@ jobs:
           # for any no_std target
           - thumbv6m-none-eabi
         backend_feature:
-          - ristretto255-voprf
           -
-          - curve25519,ristretto255-voprf
+          - ristretto255
           - curve25519
+          - ecdsa
+          - ed25519
+          - ristretto255,curve25519,ecdsa,ed25519
         frontend_feature:
           - argon2
           - serde
@@ -160,10 +166,8 @@ jobs:
       fail-fast: false
       matrix:
         backend_feature:
-          - --features ristretto255-voprf
+          - --features ristretto255
           -
-          - --features curve25519,ristretto255-voprf
-          - --features curve25519
     steps:
       - name: Checkout sources
         uses: actions/checkout@main
@@ -200,7 +204,7 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: clippy
-          args: --all-targets --features argon2,std,curve25519 -- -D warnings
+          args: --all-targets --features argon2,std,curve25519,ecdsa,ed25519 -- -D warnings
 
       - name: Run cargo doc
         uses: actions-rs/cargo@v1
@@ -208,7 +212,7 @@ jobs:
           RUSTDOCFLAGS: -D warnings
         with:
           command: doc
-          args: --no-deps --document-private-items --features argon2,std,curve25519
+          args: --no-deps --document-private-items --features argon2,std,curve25519,ecdsa,ed25519
 
   format:
     name: cargo fmt