From 7d4846c8b7f8ca1cbf40f3c1df61d318895ebdb5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pablo=20Andr=C3=A9s=20Dorado=20Su=C3=A1rez?=
 <hola@pablodorado.com>
Date: Fri, 22 Nov 2024 08:19:29 -0500
Subject: [PATCH] change(fc-pallet-pass/fc-traits-authn): rehash userId using
 the `[0, 0, ..., ...user]` array.

---
 pallets/pass/src/lib.rs | 10 +++++++---
 traits/authn/src/lib.rs |  3 ++-
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/pallets/pass/src/lib.rs b/pallets/pass/src/lib.rs
index d49e116..8d9f28e 100644
--- a/pallets/pass/src/lib.rs
+++ b/pallets/pass/src/lib.rs
@@ -6,7 +6,7 @@
 
 use fc_traits_authn::{
     util::AuthorityFromPalletId, Authenticator, DeviceChallengeResponse, DeviceId, HashedUserId,
-    UserAuthenticator, UserChallengeResponse,
+    UserAuthenticator, UserChallengeResponse, HASHED_USER_ID_LEN,
 };
 use frame_support::traits::schedule::DispatchTime;
 use frame_support::traits::Bounded;
@@ -234,8 +234,12 @@ pub mod pallet {
 
 impl<T: Config<I>, I: 'static> Pallet<T, I> {
     pub fn account_id_for(user: HashedUserId) -> Result<T::AccountId, DispatchError> {
-        let account_id: T::AccountId = T::AccountId::decode(&mut TrailingZeroInput::new(&user))
-            .map_err(|_| Error::<T, I>::AccountNotFound)?;
+        // we know the length of HashedUserId
+        let mut input = [0u8; 2 * HASHED_USER_ID_LEN];
+        input[HASHED_USER_ID_LEN..].copy_from_slice(&user);
+        let account_id: T::AccountId =
+            T::AccountId::decode(&mut TrailingZeroInput::new(&blake2_256(&input)))
+                .map_err(|_| Error::<T, I>::AccountNotFound)?;
         Ok(account_id)
     }
 
diff --git a/traits/authn/src/lib.rs b/traits/authn/src/lib.rs
index a0dcc36..b5eae4a 100644
--- a/traits/authn/src/lib.rs
+++ b/traits/authn/src/lib.rs
@@ -45,7 +45,8 @@ type CxOf<C> = <C as Challenger>::Context;
 
 pub type DeviceId = [u8; 32];
 pub type AuthorityId = [u8; 32];
-pub type HashedUserId = [u8; 32];
+pub const HASHED_USER_ID_LEN: usize = 32;
+pub type HashedUserId = [u8; HASHED_USER_ID_LEN];
 
 /// Given some context it deterministically generates a "challenge" used by authenticators
 pub trait Challenger {