diff --git a/src/process.rs b/src/process.rs
index 9d66c57..662d1c1 100644
--- a/src/process.rs
+++ b/src/process.rs
@@ -24,49 +24,65 @@ pub struct ProcessState {
 }
 
 impl ProcessState {
-    /// A state is valid if the attached validation_tokens satisfy the updated conditions defined in the encrypted_pcd
-    pub fn is_valid(&self, previous_state: Option<&ProcessState>) -> Result<bool, anyhow::Error> {
-        // Determine modified fields
-        let modified_fields: Vec<String> = if let Some(previous_state) = previous_state {
-            let res: Vec<String> = self
+    fn compute_modified_fields(&self, previous_state: Option<&ProcessState>) -> Vec<String> {
+        let new_state = &self.encrypted_pcd;
+
+        // Ensure the new state is a JSON object
+        let new_state_obj = new_state
+            .as_object()
+            .expect("New state should be a JSON object");
+
+        if let Some(prev_state) = previous_state {
+            // Previous state exists; compute differences
+            let previous_state_obj = prev_state
                 .encrypted_pcd
                 .as_object()
-                .unwrap()
+                .expect("Previous state should be a JSON object");
+
+            // Compute modified fields by comparing with previous state
+            new_state_obj
                 .iter()
                 .filter_map(|(key, value)| {
-                    let previous_value = previous_state.encrypted_pcd.get(key);
+                    let previous_value = previous_state_obj.get(key);
                     if previous_value.is_none() || value != previous_value.unwrap() {
                         Some(key.clone())
                     } else {
                         None
                     }
                 })
-                .collect();
-
-            if res.is_empty() {
-                return Err(anyhow::anyhow!("State is identical to the previous state"));
-            }
-
-            res
-        } else {
-            self.encrypted_pcd
-                .as_object()
-                .unwrap()
-                .keys()
-                .cloned()
                 .collect()
-        };
+        } else {
+            // No previous state; all fields are considered modified
+            new_state_obj.keys().cloned().collect()
+        }
+    }
+
+    pub fn is_valid(
+        &self,
+        previous_state: Option<&ProcessState>,
+    ) -> anyhow::Result<()> {
+        if self.validation_tokens.is_empty() {
+            return Err(anyhow::anyhow!("Can't validate a state with no proofs attached"));
+        }
+
+        // Compute modified fields
+        let modified_fields = self.compute_modified_fields(previous_state);
+
+        if modified_fields.is_empty() {
+            return Err(anyhow::anyhow!("State is identical to the previous state"));
+        }
+
+        println!("modified fields: {:?}", modified_fields);
+
+        // Compute the hash of the new state
+        let new_state_hash = AnkPcdHash::from_value(&self.encrypted_pcd);
 
-        // Extract roles and their definitions
         let mut fields2plains = Map::new();
         self.encrypted_pcd
             .decrypt_fields(&self.keys, &mut fields2plains)?;
 
         let mut roles2rules: HashMap<String, RoleDefinition> = HashMap::new();
         if let Some(roles) = fields2plains.get("roles") {
-            if roles.is_null() {
-                return Err(anyhow::anyhow!("Can't decrypt roles in the encrypted pcd"));
-            }
             if let Some(roles_map) = roles.as_object() {
                 for (role, conditions) in roles_map {
                     let role_def = serde_json::from_value::<RoleDefinition>(conditions.clone())?;
@@ -81,31 +97,43 @@ impl ProcessState {
 
         // Check if each modified field satisfies at least one applicable rule across all roles
         let all_fields_validated = modified_fields.iter().all(|field| {
-            let applicable_rules: Vec<(&RoleDefinition, &ValidationRule)> = roles2rules
-                .values()
-                .flat_map(|role_def| {
-                    role_def
-                        .get_applicable_rules(field)
-                        .into_iter()
-                        .map(move |rule| (role_def, rule))
-                })
+            println!("validating field: {}", field);
+            // Collect applicable rules from all roles for the current field
+            let applicable_roles: Vec<RoleDefinition> = roles2rules.iter()
+                .map(|(_, role_def)| {
+                    let mut filtered_role_def = role_def.clone();
+                    let rules = filtered_role_def.get_applicable_rules(field);
+                    filtered_role_def.validation_rules = rules.into_iter().map(|r| r.clone()).collect(); 
+                    filtered_role_def
+                }) 
                 .collect();
 
-            if applicable_rules.is_empty() {
+            if applicable_roles.is_empty() {
                 return false; // No rules apply to this field, consider it invalid
             }
 
-            applicable_rules.into_iter().any(|(role_def, rule)| {
-                rule.is_satisfied(
-                    field,
-                    AnkPcdHash::from_value(&self.encrypted_pcd),
-                    &self.validation_tokens,
-                    &role_def.members,
-                )
+            println!("applicable_roles: {:?}", applicable_roles);
+
+            // Check if any applicable rule is satisfied
+            applicable_roles.into_iter().any(|role_def| {
+                let res = false;
+                for rule in role_def.validation_rules {
+                    rule.is_satisfied(
+                        field,
+                        new_state_hash.clone(),
+                        &self.validation_tokens,
+                        &role_def.members,
+                    );
+                }
+                res
             })
         });
 
-        Ok(all_fields_validated)
+        if all_fields_validated {
+            Ok(())
+        } else {
+            Err(anyhow::anyhow!("Not enough valid proofs"))
+        }
     }
 }