fix: don't print a secret key by default

src/ristretto/ristretto_keys.rs

@@ -6,7 +6,6 @@ use std::{
     borrow::Borrow,
     cmp::Ordering,
     fmt,
-    fmt::Debug,
     hash::{Hash, Hasher},
     ops::{Add, Mul, Sub},
 };
@@ -50,7 +49,7 @@ use crate::{
 /// let _k2 = RistrettoSecretKey::from_hex(&"100000002000000030000000040000000");
 /// let _k3 = RistrettoSecretKey::random(&mut rng);
 /// ```
-#[derive(Eq, Clone, Debug, Default)]
+#[derive(Eq, Clone, Default)]
 pub struct RistrettoSecretKey(pub(crate) Scalar);
 
 const SCALAR_LENGTH: usize = 32;
@@ -111,6 +110,37 @@ impl PartialEq for RistrettoSecretKey {
     }
 }
 
+//----------------------------------   RistrettoSecretKey Debug --------------------------------------------//
+impl fmt::Debug for RistrettoSecretKey {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "RistrettoSecretKey(***)")
+    }
+}
+
+pub struct RevealedSecretKey<'a> {
+    secret: &'a RistrettoSecretKey,
+}
+
+impl RistrettoSecretKey {
+    pub fn reveal(&self) -> RevealedSecretKey<'_> {
+        RevealedSecretKey { secret: self }
+    }
+}
+
+impl<'a> fmt::Display for RevealedSecretKey<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.secret.to_hex())
+    }
+}
+
+impl<'a> fmt::Debug for RevealedSecretKey<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("RistrettoSecretKey")
+            .field(&self.secret.to_hex())
+            .finish()
+    }
+}
+
 //----------------------------------   RistrettoSecretKey Mul / Add / Sub --------------------------------------------//
 
 impl<'a, 'b> Mul<&'b RistrettoPublicKey> for &'a RistrettoSecretKey {
@@ -790,4 +820,14 @@ mod test {
             "3ae035e2663d9c561300cca67743ccdb56ea07ca7dacd8394356c4354b030e0c"
         );
     }
+
+    #[test]
+    fn visibility_test() {
+        let key =
+            RistrettoSecretKey::from_hex("b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c").unwrap();
+        let invisible = format!("{:?}", key);
+        assert!(!invisible.contains("b5bb"));
+        let visible = format!("{:?}", key.reveal());
+        assert!(visible.contains("016cc60cab13b0517dab425b1cf01179df1352f23cd32812f4850b878ae4940c"));
+    }
 }