Add getrandom to bring convenience random init functions

This is a reroll of dalek-cryptography#103 to correct branch

Co-authored-by: Ciprian Dorin Craciun <[email protected]>

Cargo.toml

@@ -50,6 +50,7 @@ harness = false
 
 [features]
 default = ["alloc", "precomputed-tables", "zeroize"]
+getrandom = ["rand_core/getrandom"]
 zeroize = ["dep:zeroize", "curve25519-dalek/zeroize"]
 serde = ["dep:serde", "curve25519-dalek/serde"]
 alloc = ["curve25519-dalek/alloc", "serde?/alloc", "zeroize?/alloc"]

src/x25519.rs

@@ -84,6 +84,11 @@ impl EphemeralSecret {
 
         EphemeralSecret(Scalar::from_bits_clamped(bytes))
     }
+    /// Generate an x25519 [`EphemeralSecret`] key using [`rand_core::OsRng`].
+    #[cfg(feature = "getrandom")]
+    pub fn random() -> Self {
+        Self::new(&mut rand_core::OsRng)
+    }
 }
 
 impl<'a> From<&'a EphemeralSecret> for PublicKey {
@@ -133,6 +138,11 @@ impl ReusableSecret {
 
         ReusableSecret(Scalar::from_bits_clamped(bytes))
     }
+    /// Generate a non-serializeable x25519 [`ReuseableSecret`] key using [`rand_core::OsRng`].
+    #[cfg(feature = "getrandom")]
+    pub fn random() -> Self {
+        Self::new(&mut rand_core::OsRng)
+    }
 }
 
 #[cfg(feature = "reusable_secrets")]
@@ -185,6 +195,12 @@ impl StaticSecret {
     pub fn to_bytes(&self) -> [u8; 32] {
         self.0.to_bytes()
     }
+
+    /// Generate an x25519 key key using [`rand_core::OsRng`].
+    #[cfg(feature = "getrandom")]
+    pub fn random() -> Self {
+        Self::new(&mut rand_core::OsRng)
+    }
 }
 
 impl From<[u8; 32]> for StaticSecret {