Adapt to chacha20

CHANGELOG.md

@@ -9,6 +9,9 @@ A [separate changelog is kept for rand_core](rand_core/CHANGELOG.md).
 You may also find the [Upgrade Guide](https://rust-random.github.io/book/update.html) useful.
 
 ## [Unreleased]
+### Changed
+- The dependency on `rand_chacha` has been replaced with a dependency on `chacha20`. This changes the implementation behind `StdRng`, but the output remains the same. There may be some API breakage when using the ChaCha-types directly as these are now the ones in `chacha20` instead of `rand_chacha`.
+
 ### Deprecated
 - Deprecate `rand::rngs::mock` module and `StepRng` generator (#1634)
 

Cargo.toml

@@ -34,7 +34,7 @@ serde = ["dep:serde", "rand_core/serde"]
 
 # Option (enabled by default): without "std" rand uses libcore; this option
 # enables functionality expected to be available on a standard platform.
-std = ["rand_core/std", "rand_chacha?/std", "alloc"]
+std = ["rand_core/std", "alloc"]
 
 # Option: "alloc" enables support for Vec and Box when not using "std"
 alloc = []
@@ -46,7 +46,7 @@ os_rng = ["rand_core/os_rng"]
 simd_support = []
 
 # Option (enabled by default): enable StdRng
-std_rng = ["dep:rand_chacha"]
+std_rng = ["dep:chacha20"]
 
 # Option: enable SmallRng
 small_rng = []
@@ -70,11 +70,16 @@ members = [
 ]
 exclude = ["benches", "distr_test"]
 
+# Force chacha20 to use the local rand_code to avoid compiling two different "rand_core"s.
+# This is necessary even if the specified versions are the same.
+[patch.crates-io]
+rand_core = { path = "rand_core" }
+
 [dependencies]
 rand_core = { path = "rand_core", version = "0.9.0", default-features = false }
 log = { version = "0.4.4", optional = true }
 serde = { version = "1.0.103", features = ["derive"], optional = true }
-rand_chacha = { path = "rand_chacha", version = "0.9.0", default-features = false, optional = true }
+chacha20 = { version = "=0.10.0-rc.0", default-features = false, features = ["rng"], optional = true }
 
 [dev-dependencies]
 rand_pcg = { path = "rand_pcg", version = "0.9.0" }

examples/rayon-monte-carlo.rs

@@ -38,8 +38,9 @@
 //! over BATCH_SIZE trials. Manually batching also turns out to be faster
 //! for the nondeterministic version of this program as well.
 
+use chacha20::ChaCha8Rng;
 use rand::distr::{Distribution, Uniform};
-use rand_chacha::{rand_core::SeedableRng, ChaCha8Rng};
+use rand_core::SeedableRng;
 use rayon::prelude::*;
 
 static SEED: u64 = 0;
@@ -56,7 +57,7 @@ fn main() {
             // We chose ChaCha because it's fast, has suitable statistical properties for simulation,
             // and because it supports this set_stream() api, which lets us choose a different stream
             // per work item. ChaCha supports 2^64 independent streams.
-            rng.set_stream(i);
+            rng.set_stream(u128::from(i));
             let mut count = 0;
             for _ in 0..BATCH_SIZE {
                 let a = range.sample(&mut rng);

rand_core/src/block.rs

@@ -557,7 +557,7 @@ mod test {
         }
         rng.next_u32();
 
-        let result = rng.next_u64();
+        let _ = rng.next_u64();
         assert_eq!(rng.index(), 1);
     }
 }

src/rngs/reseeding.rs

@@ -53,9 +53,9 @@ use rand_core::{CryptoRng, RngCore, SeedableRng, TryCryptoRng, TryRngCore};
 /// # Example
 ///
 /// ```
+/// use chacha20::ChaCha20Core; // Internal part of ChaChaRng that
+///                             // implements BlockRngCore
 /// use rand::prelude::*;
-/// use rand_chacha::ChaCha20Core; // Internal part of ChaChaRng that
-///                              // implements BlockRngCore
 /// use rand::rngs::OsRng;
 /// use rand::rngs::ReseedingRng;
 ///

src/rngs/std.rs

@@ -11,9 +11,9 @@
 use rand_core::{CryptoRng, RngCore, SeedableRng};
 
 #[cfg(any(test, feature = "os_rng"))]
-pub(crate) use rand_chacha::ChaCha12Core as Core;
+pub(crate) use chacha20::ChaCha12Core as Core;
 
-use rand_chacha::ChaCha12Rng as Rng;
+use chacha20::ChaCha12Rng as Rng;
 
 /// A strong, fast (amortized), non-portable RNG
 ///
@@ -121,4 +121,81 @@ mod test {
 
         assert_eq!([x0, x1], target);
     }
+
+    #[test]
+    fn test_chacha12_tv1_tv2() {
+        // Test vectors 1 and 2 from
+        // https://tools.ietf.org/html/draft-nir-cfrg-chacha20-poly1305-04
+        // but the expected values are replaced with the ones produced
+        // by Chacha12 (as generated by rand_chacha).
+        let seed = [0u8; 32];
+        let mut rng = StdRng::from_seed(seed);
+
+        let results: [u32; 16] = core::array::from_fn(|_| rng.next_u32());
+        let expected = [
+            1788540059, 1408849159, 315498369, 3582142047, 3150129412, 343203913, 2777219198,
+            1595256366, 2046321669, 3236133586, 875096108, 2039282348, 748642874, 426368672,
+            803736417, 3190166337,
+        ];
+        assert_eq!(results, expected);
+
+        let results = core::array::from_fn(|_| rng.next_u32());
+        let expected = [
+            1099486475, 4269030944, 863108230, 1024974988, 3085641926, 3435904281, 562369813,
+            3028926540, 3448579394, 301026465, 2545418950, 1137216539, 3393593065, 3226554768,
+            2963686439, 378791447,
+        ];
+        assert_eq!(results, expected);
+    }
+
+    #[test]
+    fn test_chacha12_tv3() {
+        // Test vector 3 from
+        // https://tools.ietf.org/html/draft-nir-cfrg-chacha20-poly1305-04
+        // but the expected values are replaced with the ones produced
+        // by Chacha12 (as generated by rand_chacha).
+        let seed = [
+            0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            0, 0, 1,
+        ];
+        let mut rng = StdRng::from_seed(seed);
+
+        // Skip block 0
+        for _ in 0..16 {
+            rng.next_u32();
+        }
+
+        let results: [u32; 16] = core::array::from_fn(|_| rng.next_u32());
+        let expected = [
+            1149489484, 1453872210, 205606722, 2561053166, 4209612569, 2282920975, 2059979989,
+            3051314295, 4135011526, 3904759261, 3697107527, 2431012387, 1801979597, 1269452364,
+            3197257745, 2154707421,
+        ];
+        assert_eq!(results, expected);
+    }
+
+    #[test]
+    fn test_chacha12_tv4() {
+        // Test vector 4 from
+        // https://tools.ietf.org/html/draft-nir-cfrg-chacha20-poly1305-04
+        // but the expected values are replaced with the ones produced
+        // by Chacha12 (as generated by rand_chacha).
+        let seed = [
+            0, 0xff, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            0, 0, 0, 0,
+        ];
+
+        // Test block 2 by skipping block 0 and 1
+        let mut rng = StdRng::from_seed(seed);
+        for _ in 0..32 {
+            rng.next_u32();
+        }
+        let results: [u32; 16] = core::array::from_fn(|_| rng.next_u32());
+        let expected = [
+            1614024310, 613097064, 193455541, 494774344, 2671734178, 1658534307, 1449802595,
+            1853279994, 129091709, 2135285029, 2884964524, 3629948889, 2335941772, 2471549797,
+            887756884, 3388159322,
+        ];
+        assert_eq!(results, expected);
+    }
 }