Make rng in TestEnv deterministic and seedable (#461)

* Move three dependent customizations into new file

* default_min_pin_length(_rp_ids) and max_rp_ids_length

* Did some backing store tricks to make the list configurable in
  TestCustomization.

* Add testing for TestCustomization

* Change assert comparison to assert_eq

* Separate tests

* Move 3 pure constants to new file

* Return Vec<String> for rp_ids()

* Make rng in TestEnv deterministic and seedable

* Move seed method to TestRng256

* Change some constant name in comments to snake case

* Move seed rng of env to the start

* Fix unused warning

* Make rng in TestEnv deterministic and seedable

* Move seed method to TestRng256

* Move seed rng of env to the start

* Fix unused warning

* Seed rng in all fuzz targets

* Fix error introduced when merging

Co-authored-by: Julien Cretin <cretin@google.com>

src/ctap/credential_management.rs

@@ -364,7 +364,6 @@ mod test {
     use super::super::CtapState;
     use super::*;
     use crate::env::test::TestEnv;
-    use crate::env::Env;
     use crypto::rng256::Rng256;
 
     const DUMMY_CHANNEL: Channel = Channel::MainHid([0x12, 0x34, 0x56, 0x78]);

src/ctap/storage.rs

@@ -726,10 +726,10 @@ mod test {
     use super::*;
     use crate::ctap::data_formats::{PublicKeyCredentialSource, PublicKeyCredentialType};
     use crate::env::test::TestEnv;
-    use crypto::rng256::{Rng256, ThreadRng256};
+    use crypto::rng256::Rng256;
 
     fn create_credential_source(
-        rng: &mut ThreadRng256,
+        rng: &mut impl Rng256,
         rp_id: &str,
         user_handle: Vec<u8>,
     ) -> PublicKeyCredentialSource {

src/env/test/mod.rs

@@ -4,21 +4,41 @@ use crate::api::firmware_protection::FirmwareProtection;
 use crate::ctap::status_code::Ctap2StatusCode;
 use crate::ctap::Channel;
 use crate::env::{Env, UserPresence};
-use crypto::rng256::ThreadRng256;
+use crypto::rng256::Rng256;
 use customization::TestCustomization;
 use persistent_store::{BufferOptions, BufferStorage, Store};
+use rand::rngs::StdRng;
+use rand::{Rng, SeedableRng};
 
 mod customization;
 mod upgrade_storage;
 
 pub struct TestEnv {
-    rng: ThreadRng256,
+    rng: TestRng256,
     user_presence: TestUserPresence,
     store: Store<BufferStorage>,
     upgrade_storage: Option<BufferUpgradeStorage>,
     customization: TestCustomization,
 }
 
+pub struct TestRng256 {
+    rng: StdRng,
+}
+
+impl TestRng256 {
+    pub fn seed_rng_from_u64(&mut self, state: u64) {
+        self.rng = StdRng::seed_from_u64(state);
+    }
+}
+
+impl Rng256 for TestRng256 {
+    fn gen_uniform_u8x32(&mut self) -> [u8; 32] {
+        let mut result = [Default::default(); 32];
+        self.rng.fill(&mut result);
+        result
+    }
+}
+
 pub struct TestUserPresence {
     check: Box<dyn Fn(Channel) -> Result<(), Ctap2StatusCode>>,
 }
@@ -48,7 +68,9 @@ fn new_storage() -> BufferStorage {
 
 impl TestEnv {
     pub fn new() -> Self {
-        let rng = ThreadRng256 {};
+        let rng = TestRng256 {
+            rng: StdRng::seed_from_u64(0),
+        };
         let user_presence = TestUserPresence {
             check: Box::new(|_| Ok(())),
         };
@@ -72,6 +94,10 @@ impl TestEnv {
     pub fn customization_mut(&mut self) -> &mut TestCustomization {
         &mut self.customization
     }
+
+    pub fn rng(&mut self) -> &mut TestRng256 {
+        &mut self.rng
+    }
 }
 
 impl TestUserPresence {
@@ -93,7 +119,7 @@ impl FirmwareProtection for TestEnv {
 }
 
 impl Env for TestEnv {
-    type Rng = ThreadRng256;
+    type Rng = TestRng256;
     type UserPresence = TestUserPresence;
     type Storage = BufferStorage;
     type UpgradeStorage = BufferUpgradeStorage;