reputation-proof.md

description
The zero-knowledge circuit of reputation proof in UniRep

Reputation Proof

Users can use a reputation proof to claim that how the reputation is from a given attester. There are following things that user can choose to prove:

1. The pos_rep - neg_rep given by the attester is more than the claimed min_rep i.e.

   (pos_rep - neg_rep) > min_rep
   

2. The graffiti_preimage of a graffiti i.e.

   hash(graffiti_preimage) == graffiti
   

3. The reputation nullifiers are computed correctly i.e.

   // for all nonces
   nonce >= 0
   nonce < pos_rep - neg_rep
   reputation_nullifiers = hash5(
       REPUTATION_NULLIFIER_DOMAIN, 
       identity_nullifier, 
       epoch, 
       nonce, 
       attesterId
   )
   

The circuit also checks if the user has registered and performed user state transition in the claimed epoch.

Public inputs

• epoch
• epoch_key
• GST_root
• attester_id
• rep_nullifiers_amount
• min_rep
• prove_graffiti
• graffiti_pre_image

Public outputs

• rep_nullifiers

Private inputs

• epoch_key_nonce
• identity_nullifier
• identity_trapdoor
• user_tree_root
• GST_path_index
• GST_path_elements
• pos_rep
• neg_rep
• graffiti
• sign_up
• UST_path_elements
• selectors
• rep_nonce

Contraints

1. Check if user exists in the Global State Tree and verify epoch key

Check the constrains in epoch key proof.

{% hint style="info" %} See: Epoch Key Proof circuit {% endhint %}

2. Check if the reputation given by the attester is in the user state tree

Check if hash(pos_rep, neg_rep, graffiti, sign_up) is one of the leaves in the user state tree of root user_tree_root.

3. Check if reputation nullifiers are valid

Check if rep_nonce[i] < pos_rep - neg_rep for all output rep_nullifiers[i].

Check if

rep_nullifier[i] = hash(
    REPUTATION_NULLIFIER_DOMAIN = 2, 
    identity_nullifier, 
    epoch, 
    rep_nonce[i], 
    attester_id
)

{% hint style="info" %} See: Reputation nullifiers {% endhint %}

4. Check if user has reputation greater than min_rep

Check if

1. min_rep > 0
2. pos_rep - neg_rep >= 0
3. pos_rep - neg_rep >= min_rep

5. Check pre-image of graffiti

Check if hash(graffiti_pre_image) == graffiti.

{% hint style="info" %} See the whole circuit in circuits/proveReputation.circom {% endhint %}