Use riffle_shuffle in std's MockApi

packages/std/src/mock.rs

@@ -88,11 +88,13 @@ impl Api for MockApi {
         }
 
         let mut out = Vec::from(human.as_str());
-        let append = self.canonical_length - out.len();
-        if append > 0 {
-            out.extend(vec![0u8; append]);
+        // pad to canonical_length wil NULL bytes
+        out.resize(self.canonical_length, 0x00);
+        // shuffle to destroy the most obvious structure (https://github.com/CosmWasm/cosmwasm/issues/552)
+        for _ in 0..18 {
+            out = riffle_shuffle(&out);
         }
-        Ok(CanonicalAddr(Binary(out)))
+        Ok(out.into())
     }
 
     fn human_address(&self, canonical: &CanonicalAddr) -> StdResult<HumanAddr> {
@@ -102,16 +104,16 @@ impl Api for MockApi {
             ));
         }
 
-        // remove trailing 0's (TODO: fix this - but fine for first tests)
-        let trimmed: Vec<u8> = canonical
-            .as_slice()
-            .iter()
-            .cloned()
-            .filter(|&x| x != 0)
-            .collect();
+        let mut tmp: Vec<u8> = canonical.clone().into();
+        // Shuffle two more times which restored the original value (24 elements are back to original after 20 rounds)
+        for _ in 0..2 {
+            tmp = riffle_shuffle(&tmp);
+        }
+        // Remove NULL bytes (i.e. the padding)
+        let trimmed = tmp.into_iter().filter(|&x| x != 0x00).collect();
         // decode UTF-8 bytes into string
         let human = String::from_utf8(trimmed).map_err(StdError::invalid_utf8)?;
-        Ok(HumanAddr(human))
+        Ok(human.into())
     }
 
     fn debug(&self, message: &str) {