Replaces Rng256 with new Rng API (#612)

* Replaces the Rng256 with RngCore from rand_core

The old trait was designed with our software crypto in mind. We should
use a more standard API going forward.

- Removes libraries/rng256/
- Ports libraries/crypto/ to rand_core
- Moves the used RNG trait to api/

* Use StdRng directy in TestEnv

libraries/opensk/Cargo.toml

@@ -14,16 +14,15 @@ rust-version = "1.47"
 [dependencies]
 sk-cbor = { path = "../cbor" }
 crypto = { path = "../crypto" }
-rng256 = { path = "../rng256" }
 persistent_store = { path = "../persistent_store" }
 byteorder = { version = "1", default-features = false }
 arrayref = "0.3.6"
 subtle = { version = "2.2", default-features = false, features = ["nightly"] }
 arbitrary = { version = "0.4.7", features = ["derive"], optional = true }
-rand = { version = "0.8.4", optional = true }
 ed25519-compact = { version = "1", default-features = false, optional = true }
 p256 = { version = "0.13.0", features = ["ecdh"], optional = true }
-rand_core = { version = "0.6.4", optional = true }
+rand_core = "0.6.4"
+rand = { version = "0.8.5", optional = true }
 sha2 = { version = "0.10.6", optional = true }
 hmac = { version = "0.12.1", optional = true }
 hkdf = { version = "0.12.3", optional = true }
@@ -32,12 +31,12 @@ cbc = { version = "0.1.2", optional = true }
 
 [features]
 debug_ctap = []
-std = ["crypto/std", "persistent_store/std", "rng256/std", "rand"]
+std = ["crypto/std", "persistent_store/std", "rand"]
 with_ctap1 = ["crypto/with_ctap1"]
 vendor_hid = []
 fuzz = ["arbitrary", "std"]
 ed25519 = ["ed25519-compact"]
-rust_crypto = ["p256", "rand_core", "sha2", "hmac", "hkdf", "aes", "cbc"]
+rust_crypto = ["p256", "sha2", "hmac", "hkdf", "aes", "cbc"]
 
 [dev-dependencies]
 enum-iterator = "0.6.0"