No Pod IDs (#394)

- middleware:
  - Add `Statement::Intro`
  - Add `SignedBy` native predicate and operation.  The signature is auxiliary data to the operation
  - Rename `PodSigner` to `Signer` with a new API (just for signing `RawValue`)
  - Removed `NewEntry` operation.  Use `ContainsFromEntries` instead
  - Remove `KEY_SIGNER` and `KEY_TYPE` which are no longer used
  - Merge `RecursivePod` and `Pod` traits
  - Change the `Pod::deserialize_data` method to use `Self` instead of `Box<dyn Pod>` 
  - Extend `Pod` trait with these methods:
    - `is_main`: when the pod is Main, in a (recursive) verification its vk will be checked to exist in the vd_set but not if it's intro pod
    - `is_mock`: skip some verifications in the recursive mock MainPod verification
    - `verifier_data_hash`
    - `pod_id` renamed to `statements_hash`
  - AnchoredKeys are now a pair of dictionary root and key
  - Entry statements are now defined as Contains with literal arguments
    - Operations that take Entries now use Contains statements with literal arguments
- frontend:
  - Rename `SignedPod` to `SignedDict` (which now contains the dict, public key and signature, and can still `verify(self)`ed)
  - The `SignedDict` keeps the method `get_statement` for convenience but now it returns a `Contains` statement that proves the existence of the key in the dict
  - The `MainPodBuilder` automatically inserts a `Contains` statement when an operation is added that uses an entry as argument that was not yet "opened".
  - Removed the `literal` methods from the `MainPodBuilder` that were loading literals to anchored keys: that was no longer needed after we introduced literal arguments
- backend
  - Only verify inclusion of the verifying key into the vd_set if the pod is MainPod.  A pod is not MainPod if the first statement is Intro.
  - Reject intro pods that have non-intro statements
  - Empty pod now returns an intro statement
  - Don't insert a type statement automatically in MainPod and MockMainPod.  We get rid of the type entry.
  - Implement `SignedBy` operation, which uses the muxed table to store signature verifications
- Rename `PodId` to `statements_hash` or `sts_hash` for short.  Now this is only used as a hash of the statements for the circuits public inputs.
- Refactor normalization of `self` statements:
  - Before: replace values that contain `SELF` by the given pod_id
  - After: place the verifying key hash into the Intro predicates

src/frontend/pod_request.rs

@@ -128,8 +128,8 @@ impl PodRequest {
                 }
 
                 // Try to bind wildcard to the POD ID
-                let pod_id_value = Value::from(stmt_key.pod_id);
-                self.try_bind_wildcard(&wildcard.name, pod_id_value, current_bindings, new_bindings)
+                let root_value = Value::from(stmt_key.root);
+                self.try_bind_wildcard(&wildcard.name, root_value, current_bindings, new_bindings)
             }
 
             // Other combinations don't match
@@ -176,12 +176,14 @@ impl Display for PodRequest {
 mod tests {
     use crate::{
         backends::plonky2::{
-            mock::mainpod::MockProver, primitives::ec::schnorr::SecretKey, signedpod::Signer,
+            mock::mainpod::MockProver, primitives::ec::schnorr::SecretKey, signer::Signer,
+        },
+        examples::{
+            zu_kyc_pod_builder, zu_kyc_pod_request, zu_kyc_sign_dict_builders, MOCK_VD_SET,
         },
-        examples::{zu_kyc_pod_builder, zu_kyc_pod_request, zu_kyc_sign_pod_builders, MOCK_VD_SET},
         frontend::{MainPodBuilder, Operation},
         lang::parse,
-        middleware::Params,
+        middleware::{Params, Value},
     };
 
     #[test]
@@ -189,7 +191,7 @@ mod tests {
         let params = Params::default();
         let vd_set = &*MOCK_VD_SET;
 
-        let (gov_id, pay_stub) = zu_kyc_sign_pod_builders(&params);
+        let (gov_id, pay_stub) = zu_kyc_sign_dict_builders(&params);
         let gov_id = gov_id.sign(&Signer(SecretKey(1u32.into()))).unwrap();
         let pay_stub = pay_stub.sign(&Signer(SecretKey(2u32.into()))).unwrap();
         let builder = zu_kyc_pod_builder(&Params::default(), vd_set, &gov_id, &pay_stub).unwrap();
@@ -198,8 +200,8 @@ mod tests {
 
         // This request matches the POD
         let request = zu_kyc_pod_request(
-            gov_id.get("_signer").unwrap(),
-            pay_stub.get("_signer").unwrap(),
+            &Value::from(gov_id.public_key),
+            &Value::from(pay_stub.public_key),
         )
         .unwrap();
         assert!(request.exact_match_pod(&*kyc.pod).is_ok());