curve: Implement ConditionallySelectable for MontgomeryPoint (#677)

elichai · web-flow · commit 79ab6c29bd90 · 2024-07-30T01:51:44.000-04:00
diff --git a/curve25519-dalek/Cargo.toml b/curve25519-dalek/Cargo.toml
@@ -51,7 +51,7 @@ ff = { version = "0.13", default-features = false, optional = true }
 group = { version = "0.13", default-features = false, optional = true }
 rand_core = { version = "0.6.4", default-features = false, optional = true }
 digest = { version = "0.10", default-features = false, optional = true }
-subtle = { version = "2.6.0", default-features = false }
+subtle = { version = "2.6.0", default-features = false, features = ["const-generics"]}
 serde = { version = "1.0", default-features = false, optional = true, features = ["derive"] }
 zeroize = { version = "1", default-features = false, optional = true }
 
diff --git a/curve25519-dalek/src/montgomery.rs b/curve25519-dalek/src/montgomery.rs
@@ -84,6 +84,12 @@ impl ConstantTimeEq for MontgomeryPoint {
     }
 }
 
+impl ConditionallySelectable for MontgomeryPoint {
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        Self(<[u8; 32]>::conditional_select(&a.0, &b.0, choice))
+    }
+}
+
 impl PartialEq for MontgomeryPoint {
     fn eq(&self, other: &MontgomeryPoint) -> bool {
         self.ct_eq(other).into()

Original file line number	Diff line number	Diff line change
`@@ -84,6 +84,12 @@ impl ConstantTimeEq for MontgomeryPoint {`
`84`	`84`	`}`
`85`	`85`	`}`
`86`	`86`
	`87`	`+impl ConditionallySelectable for MontgomeryPoint {`
	`88`	`+ fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {`
	`89`	`+ Self(<[u8; 32]>::conditional_select(&a.0, &b.0, choice))`
	`90`	`+ }`
	`91`	`+}`
	`92`	`+`
`87`	`93`	`impl PartialEq for MontgomeryPoint {`
`88`	`94`	`fn eq(&self, other: &MontgomeryPoint) -> bool {`
`89`	`95`	`self.ct_eq(other).into()`