serde support for ChaCha

rand_chacha/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "rand_chacha"
-version = "0.3.0"
+version = "0.3.1"
 authors = ["The Rand Project Developers", "The Rust Project Developers", "The CryptoCorrosion Contributors"]
 license = "MIT OR Apache-2.0"
 readme = "README.md"
@@ -17,8 +17,14 @@ edition = "2018"
 [dependencies]
 rand_core = { path = "../rand_core", version = "0.6.0" }
 ppv-lite86 = { version = "0.2.8", default-features = false, features = ["simd"] }
+serde = { version = "1.0", features = ["derive"], optional = true }
+
+[dev-dependencies]
+# Only to test serde1
+serde_json = "1.0"
 
 [features]
 default = ["std"]
 std = ["ppv-lite86/std"]
 simd = [] # deprecated
+serde1 = ["serde"]

rand_chacha/src/chacha.rs

@@ -16,6 +16,8 @@ use crate::guts::ChaCha;
 use rand_core::block::{BlockRng, BlockRngCore};
 use rand_core::{CryptoRng, Error, RngCore, SeedableRng};
 
+#[cfg(feature = "serde1")] use serde::{Serialize, Deserialize, Serializer, Deserializer};
+
 const STREAM_PARAM_NONCE: u32 = 1;
 const STREAM_PARAM_BLOCK: u32 = 0;
 
@@ -69,7 +71,7 @@ impl<T> fmt::Debug for Array64<T> {
 }
 
 macro_rules! chacha_impl {
-    ($ChaChaXCore:ident, $ChaChaXRng:ident, $rounds:expr, $doc:expr) => {
+    ($ChaChaXCore:ident, $ChaChaXRng:ident, $rounds:expr, $doc:expr, $abst:ident) => {
         #[doc=$doc]
         #[derive(Clone, PartialEq, Eq)]
         pub struct $ChaChaXCore {
@@ -245,6 +247,24 @@ macro_rules! chacha_impl {
                     self.set_word_pos(wp);
                 }
             }
+
+            /// Get the stream number.
+            #[inline]
+            pub fn get_stream(&self) -> u64 {
+                self.rng
+                    .core
+                    .state
+                    .get_stream_param(STREAM_PARAM_NONCE)
+            }
+
+            /// Get the seed.
+            #[inline]
+            pub fn get_seed(&self) -> [u8; 32] {
+                self.rng
+                    .core
+                    .state
+                    .get_seed()
+            }
         }
 
         impl CryptoRng for $ChaChaXRng {}
@@ -259,24 +279,129 @@ macro_rules! chacha_impl {
 
         impl PartialEq<$ChaChaXRng> for $ChaChaXRng {
             fn eq(&self, rhs: &$ChaChaXRng) -> bool {
-                self.rng.core.state.stream64_eq(&rhs.rng.core.state)
-                    && self.get_word_pos() == rhs.get_word_pos()
+                let a: $abst::$ChaChaXRng = self.into();
+                let b: $abst::$ChaChaXRng = rhs.into();
+                a == b
             }
         }
         impl Eq for $ChaChaXRng {}
+
+        #[cfg(feature = "serde1")]
+        impl Serialize for $ChaChaXRng {
+            fn serialize<S>(&self, s: S) -> Result<S::Ok, S::Error>
+            where S: Serializer {
+                $abst::$ChaChaXRng::from(self).serialize(s)
+            }
+        }
+        #[cfg(feature = "serde1")]
+        impl<'de> Deserialize<'de> for $ChaChaXRng {
+            fn deserialize<D>(d: D) -> Result<Self, D::Error> where D: Deserializer<'de> {
+                $abst::$ChaChaXRng::deserialize(d).map(|x| Self::from(&x))
+            }
+        }
+
+        mod $abst {
+            #[cfg(feature = "serde1")] use serde::{Serialize, Deserialize};
+
+            // The abstract state of a ChaCha stream, independent of implementation choices. The
+            // comparison and serialization of this object is considered a semver-covered part of
+            // the API.
+            #[derive(Debug, PartialEq, Eq)]
+            #[cfg_attr(
+                feature = "serde1",
+                derive(Serialize, Deserialize),
+            )]
+            pub(crate) struct $ChaChaXRng {
+                seed: [u8; 32],
+                stream: u64,
+                word_pos: u128,
+            }
+
+            impl From<&super::$ChaChaXRng> for $ChaChaXRng {
+                // Forget all information about the input except what is necessary to determine the
+                // outputs of any sequence of pub API calls.
+                fn from(r: &super::$ChaChaXRng) -> Self {
+                    Self {
+                        seed: r.get_seed(),
+                        stream: r.get_stream(),
+                        word_pos: r.get_word_pos(),
+                    }
+                }
+            }
+
+            impl From<&$ChaChaXRng> for super::$ChaChaXRng {
+                // Construct one of the possible concrete RNGs realizing an abstract state.
+                fn from(a: &$ChaChaXRng) -> Self {
+                    use rand_core::SeedableRng;
+                    let mut r = Self::from_seed(a.seed);
+                    r.set_stream(a.stream);
+                    r.set_word_pos(a.word_pos);
+                    r
+                }
+            }
+        }
     }
 }
 
-chacha_impl!(ChaCha20Core, ChaCha20Rng, 10, "ChaCha with 20 rounds");
-chacha_impl!(ChaCha12Core, ChaCha12Rng, 6, "ChaCha with 12 rounds");
-chacha_impl!(ChaCha8Core, ChaCha8Rng, 4, "ChaCha with 8 rounds");
+chacha_impl!(ChaCha20Core, ChaCha20Rng, 10, "ChaCha with 20 rounds", abstract20);
+chacha_impl!(ChaCha12Core, ChaCha12Rng, 6, "ChaCha with 12 rounds", abstract12);
+chacha_impl!(ChaCha8Core, ChaCha8Rng, 4, "ChaCha with 8 rounds", abstract8);
 
 #[cfg(test)]
 mod test {
     use rand_core::{RngCore, SeedableRng};
 
+    #[cfg(feature = "serde1")] use super::{ChaCha20Rng, ChaCha12Rng, ChaCha8Rng};
+
     type ChaChaRng = super::ChaCha20Rng;
 
+    #[cfg(feature = "serde1")]
+    #[test]
+    fn test_chacha_serde_roundtrip() {
+        let seed = [
+            1, 0, 52, 0, 0, 0, 0, 0, 1, 0, 10, 0, 22, 32, 0, 0, 2, 0, 55, 49, 0, 11, 0, 0, 3, 0, 0, 0, 0,
+            0, 2, 92,
+        ];
+        let mut rng1 = ChaCha20Rng::from_seed(seed);
+        let mut rng2 = ChaCha12Rng::from_seed(seed);
+        let mut rng3 = ChaCha8Rng::from_seed(seed);
+
+        let encoded1 = serde_json::to_string(&rng1).unwrap();
+        let encoded2 = serde_json::to_string(&rng2).unwrap();
+        let encoded3 = serde_json::to_string(&rng3).unwrap();
+
+        let mut decoded1: ChaCha20Rng = serde_json::from_str(&encoded1).unwrap();
+        let mut decoded2: ChaCha12Rng = serde_json::from_str(&encoded2).unwrap();
+        let mut decoded3: ChaCha8Rng = serde_json::from_str(&encoded3).unwrap();
+
+        assert_eq!(rng1, decoded1);
+        assert_eq!(rng2, decoded2);
+        assert_eq!(rng3, decoded3);
+
+        assert_eq!(rng1.next_u32(), decoded1.next_u32());
+        assert_eq!(rng2.next_u32(), decoded2.next_u32());
+        assert_eq!(rng3.next_u32(), decoded3.next_u32());
+    }
+
+    // This test validates that:
+    // 1. a hard-coded serialization demonstrating the format at time of initial release can still
+    //    be deserialized to a ChaChaRng
+    // 2. re-serializing the resultant object produces exactly the original string
+    //
+    // Condition 2 is stronger than necessary: an equivalent serialization (e.g. with field order
+    // permuted, or whitespace differences) would also be admissible, but would fail this test.
+    // However testing for equivalence of serialized data is difficult, and there shouldn't be any
+    // reason we need to violate the stronger-than-needed condition, e.g. by changing the field
+    // definition order.
+    #[cfg(feature = "serde1")]
+    #[test]
+    fn test_chacha_serde_format_stability() {
+        let j = r#"{"seed":[4,8,15,16,23,42,4,8,15,16,23,42,4,8,15,16,23,42,4,8,15,16,23,42,4,8,15,16,23,42,4,8],"stream":27182818284,"word_pos":314159265359}"#;
+        let r: ChaChaRng = serde_json::from_str(&j).unwrap();
+        let j1 = serde_json::to_string(&r).unwrap();
+        assert_eq!(j, j1);
+    }
+
     #[test]
     fn test_chacha_construction() {
         let seed = [

rand_chacha/src/guts.rs

@@ -92,12 +92,9 @@ impl ChaCha {
         get_stream_param(self, param)
     }
 
-    /// Return whether rhs is equal in all parameters except current 64-bit position.
-    #[inline]
-    pub fn stream64_eq(&self, rhs: &Self) -> bool {
-        let self_d: [u32; 4] = self.d.into();
-        let rhs_d: [u32; 4] = rhs.d.into();
-        self.b == rhs.b && self.c == rhs.c && self_d[3] == rhs_d[3] && self_d[2] == rhs_d[2]
+    #[inline(always)]
+    pub fn get_seed(&self) -> [u8; 32] {
+        get_seed(self)
     }
 }
 
@@ -205,6 +202,17 @@ dispatch_light128!(m, Mach, {
     }
 });
 
+dispatch_light128!(m, Mach, {
+    fn get_seed(state: &ChaCha) -> [u8; 32] {
+        let b: Mach::u32x4 = m.unpack(state.b);
+        let c: Mach::u32x4 = m.unpack(state.c);
+        let mut key = [0u8; 32];
+        b.write_le(&mut key[..16]);
+        c.write_le(&mut key[16..]);
+        key
+    }
+});
+
 fn read_u32le(xs: &[u8]) -> u32 {
     assert_eq!(xs.len(), 4);
     u32::from(xs[0]) | (u32::from(xs[1]) << 8) | (u32::from(xs[2]) << 16) | (u32::from(xs[3]) << 24)