Centralize dependency on Rng instance

Use tink_core::subtle::random::rng() to return an instance of the
tink_core::subtle::random::Generator trait, which is just a combination
of rand::RngCore and rand::CryptoRng.

Use this rng() instance throughout the code.

Drop a couple of direct dependencies on rand which were not needed.

aead/Cargo.toml

@@ -19,7 +19,6 @@ aes-gcm = "^0.9.2"
 aes-gcm-siv = "^0.10"
 chacha20poly1305 = "^0.9"
 generic-array = "^0.14.4"
-rand = "^0.7"
 tink-core = "^0.2"
 tink-mac = "^0.2"
 tink-proto = "^0.2"

core/src/keyset/manager.rs

@@ -209,7 +209,7 @@ impl Manager {
 
     /// Generate a key id that has not been used by any key in the [`Keyset`](tink_proto::Keyset).
     fn new_key_id(&self) -> KeyId {
-        let mut rng = rand::thread_rng();
+        let mut rng = crate::subtle::random::rng();
 
         loop {
             let ret = rng.gen::<u32>();

core/src/subtle/random.rs

@@ -16,16 +16,32 @@
 
 //! Utilities for random data.
 
-use rand::{thread_rng, Rng};
+/// Re-export the particular version of the `rand` crate whose types appear in the API.
+pub use rand;
+
+use rand::Rng;
+
+/// Trait that encapsulates the required traits that a random number generator instance must
+/// implement.
+pub trait Generator: rand::RngCore + rand::CryptoRng {}
+
+/// Blanket implementation: any type that is a [`rand::CryptoRng`] is automatically
+/// suitable as a Tink [`Generator`].
+impl<T> Generator for T where T: rand::RngCore + rand::CryptoRng {}
+
+/// Return a random number generator suitable for cryptographic operation.
+pub fn rng() -> Box<dyn Generator> {
+    Box::new(rand::thread_rng())
+}
 
 /// Return a vector of the given `size` filled with random bytes.
 pub fn get_random_bytes(size: usize) -> Vec<u8> {
     let mut data = vec![0u8; size];
-    thread_rng().fill(&mut data[..]);
+    rng().fill(&mut data[..]);
     data
 }
 
 /// Randomly generate an unsigned 32-bit integer.
 pub fn get_random_uint32() -> u32 {
-    thread_rng().gen()
+    rng().gen()
 }

signature/src/ed25519_signer_key_manager.rs

@@ -47,7 +47,7 @@ impl tink_core::registry::KeyManager for Ed25519SignerKeyManager {
     }
 
     fn new_key(&self, _serialized_key_format: &[u8]) -> Result<Vec<u8>, TinkError> {
-        let mut csprng = rand::rngs::OsRng {};
+        let mut csprng = tink_core::subtle::random::rng();
         let keypair = ed25519_dalek::Keypair::generate(&mut csprng);
 
         let public_proto = tink_proto::Ed25519PublicKey {

streaming/Cargo.toml

@@ -15,7 +15,6 @@ categories = ["cryptography"]
 aes = { version = "^0.7.4", features = ["ctr"] }
 # Need the `std` feature for Error type conversion
 aes-gcm = { version = "^0.9.2", features = ["std"] }
-rand = "^0.7"
 tink-core = "^0.2"
 tink-mac = "^0.2"
 tink-proto = "^0.2"

tests/src/lib.rs

@@ -394,7 +394,7 @@ pub fn get_ecdsa_params(
 /// Create an [`Ed25519PrivateKey`](tink_proto::Ed25519PrivateKey) with randomly generated key
 /// material.
 pub fn new_ed25519_private_key() -> tink_proto::Ed25519PrivateKey {
-    let mut csprng = rand::thread_rng();
+    let mut csprng = tink_core::subtle::random::rng();
     let keypair = ed25519_dalek::Keypair::generate(&mut csprng);
 
     let public_proto = tink_proto::Ed25519PublicKey {

tests/tests/aead/subtle/chacha20poly1305_test.rs

@@ -15,10 +15,12 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 use super::{chacha20poly1305_vectors::*, wycheproof::*};
-use rand::{thread_rng, Rng};
 use std::collections::HashSet;
 use tink_aead::subtle;
-use tink_core::{subtle::random::get_random_bytes, Aead};
+use tink_core::{
+    subtle::random::{get_random_bytes, rand::Rng},
+    Aead,
+};
 use tink_tests::WycheproofResult;
 
 #[test]
@@ -172,7 +174,7 @@ fn test_cha_cha20_poly1305_modify_ciphertext() {
             .unwrap_or_else(|e| panic!("#{}: encrypt failed: {:?}", i, e));
 
         if !aad.is_empty() {
-            let alter_aad_idx = thread_rng().gen_range(0, aad.len());
+            let alter_aad_idx = tink_core::subtle::random::rng().gen_range(0, aad.len());
             aad[alter_aad_idx] ^= 0x80;
             assert!(
                 ca.decrypt(&ct, &aad).is_err(),
@@ -182,7 +184,7 @@ fn test_cha_cha20_poly1305_modify_ciphertext() {
             aad[alter_aad_idx] ^= 0x80;
         }
 
-        let alter_ct_idx = thread_rng().gen_range(0, ct.len());
+        let alter_ct_idx = tink_core::subtle::random::rng().gen_range(0, ct.len());
         ct[alter_ct_idx] ^= 0x80;
         assert!(
             ca.decrypt(&ct, &aad).is_err(),

tests/tests/aead/subtle/xchacha20poly1305_test.rs

@@ -15,10 +15,12 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 use super::{wycheproof::*, xchacha20poly1305_vectors::*};
-use rand::{thread_rng, Rng};
 use std::collections::HashSet;
 use tink_aead::subtle;
-use tink_core::{subtle::random::get_random_bytes, Aead};
+use tink_core::{
+    subtle::random::{get_random_bytes, rand::Rng},
+    Aead,
+};
 use tink_tests::WycheproofResult;
 
 #[test]
@@ -173,7 +175,7 @@ fn test_x_cha_cha20_poly1305_modify_ciphertext() {
             .unwrap_or_else(|e| panic!("#{}: encrypt failed: {:?}", i, e));
 
         if !aad.is_empty() {
-            let alter_aad_idx = thread_rng().gen_range(0, aad.len());
+            let alter_aad_idx = tink_core::subtle::random::rng().gen_range(0, aad.len());
             aad[alter_aad_idx] ^= 0x80;
             assert!(
                 ca.decrypt(&ct, &aad).is_err(),
@@ -183,7 +185,7 @@ fn test_x_cha_cha20_poly1305_modify_ciphertext() {
             aad[alter_aad_idx] ^= 0x80;
         }
 
-        let alter_ct_idx = thread_rng().gen_range(0, ct.len());
+        let alter_ct_idx = tink_core::subtle::random::rng().gen_range(0, ct.len());
         ct[alter_ct_idx] ^= 0x80;
         assert!(
             ca.decrypt(&ct, &aad).is_err(),

tests/tests/signature/subtle/ed25519_signer_verifier_test.rs

@@ -23,7 +23,7 @@ use tink_tests::WycheproofResult;
 #[test]
 fn test_ed25519_deterministic() {
     let data = get_random_bytes(20);
-    let mut csprng = rand::thread_rng();
+    let mut csprng = tink_core::subtle::random::rng();
     let keypair = Keypair::generate(&mut csprng);
 
     // Use the private key and public key directly to create new instances
@@ -46,7 +46,7 @@ fn test_ed25519_deterministic() {
 #[test]
 fn test_ed25519_verify_modified_signature() {
     let data = get_random_bytes(20);
-    let mut csprng = rand::thread_rng();
+    let mut csprng = tink_core::subtle::random::rng();
     let keypair = Keypair::generate(&mut csprng);
 
     // Use the private key and public key directly to create new instances
@@ -73,7 +73,7 @@ fn test_ed25519_verify_modified_signature() {
 #[test]
 fn test_ed25519_verify_truncated_signature() {
     let data = get_random_bytes(20);
-    let mut csprng = rand::thread_rng();
+    let mut csprng = tink_core::subtle::random::rng();
     let keypair = Keypair::generate(&mut csprng);
 
     // Use the private key and public key directly to create new instances
@@ -89,7 +89,7 @@ fn test_ed25519_verify_truncated_signature() {
 #[test]
 fn test_ed25519_verify_modified_message() {
     let mut data = get_random_bytes(20);
-    let mut csprng = rand::thread_rng();
+    let mut csprng = tink_core::subtle::random::rng();
     let keypair = Keypair::generate(&mut csprng);
 
     // Use the private key and public key directly to create new instances
@@ -114,7 +114,7 @@ fn test_ed25519_verify_modified_message() {
 }
 #[test]
 fn test_ed25519_sign_verify() {
-    let mut csprng = rand::thread_rng();
+    let mut csprng = tink_core::subtle::random::rng();
     let keypair = Keypair::generate(&mut csprng);
     let seed = keypair.secret.as_bytes().to_vec();
 

tests/tests/streaming/integration_test.rs

@@ -174,7 +174,8 @@ impl std::io::Read for PartialReader {
     // when more data is available. This is valid for Rust's `std::io::Read`, but
     // would not be valid for an `io::Writer` in Go.
     fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
-        if rand::thread_rng().gen_range(0, 3) == 0 {
+        let mut csprng = tink_core::subtle::random::rng();
+        if csprng.gen_range(0, 3) == 0 {
             // Randomly pretend to have been interrupted.
             return Err(std::io::Error::new(
                 std::io::ErrorKind::Interrupted,