kem: re-export Generate; add getrandom feature (#2140)

Since KEMs require randomness and unconditionally enables the
`rand_core` feature of `crypto-common`, this unconditionally re-exports
the `Generate` trait, which can be used to generate decapsulation keys
(though the bounds on `Decapsulate` remain unchanged).

This also adds a passthrough feature for `getrandom` to enable
`crypto-common/getrandom`. Ideally this would also add a method to
`Encapsulate` which can use `getrandom::SysRng` as the RNG for
encapsulating, but since there isn't yet a prerelease with that feature
this doesn't attempt to add it yet.

Author: tarcieri

Cargo.lock

@@ -13,12 +13,15 @@ categories = ["cryptography", "no-std"]
 description = "Traits for key encapsulation mechanisms"
 
 [dependencies]
-crypto-common = { version = "0.2.0-rc.5", features = ["rand_core"], path = "../crypto-common" }
+crypto-common = { version = "0.2.0-rc.6", features = ["rand_core"], path = "../crypto-common" }
 rand_core = "0.10.0-rc-3"
-zeroize = { version = "1.7", default-features = false }
+
+[features]
+getrandom = ["crypto-common/getrandom"]
 
 [package.metadata.docs.rs]
 all-features = true
 
+# TODO(tarcieri): make README.md an actually valid example
 [lib]
 doctest = false

kem/Cargo.toml

@@ -8,7 +8,7 @@
 #![forbid(unsafe_code)]
 #![warn(missing_docs, unused_qualifications, missing_debug_implementations)]
 
-pub use crypto_common::{KeyInit, KeySizeUser, typenum::consts};
+pub use crypto_common::{Generate, KeyInit, KeySizeUser, typenum::consts};
 
 use rand_core::TryCryptoRng;