diff --git a/BrightID.sol b/BrightID.sol
index 7c719cd..e88574b 100644
--- a/BrightID.sol
+++ b/BrightID.sol
@@ -7,25 +7,27 @@ import "./IBrightID.sol";
 contract BrightID is Ownable, IBrightID {
     IERC20 public verifierToken;
     bytes32 public app;
+    bytes32 public verificationHash;
 
-    event Verified(address indexed addr);
     event VerifierTokenSet(IERC20 verifierToken);
     event AppSet(bytes32 _app);
+    event VerificationHashSet(bytes32 verificationHash);
 
     struct Verification {
         uint256 time;
         bool isVerified;
     }
     mapping(address => Verification) public verifications;
-    mapping(address => address) override public history;
 
     /**
      * @param _verifierToken verifier token
      * @param _app BrightID app used for verifying users
+     * @param _verificationHash sha256 of the verification expression
      */
-    constructor(IERC20 _verifierToken, bytes32 _app) public {
+    constructor(IERC20 _verifierToken, bytes32 _app, bytes32 _verificationHash) public {
         verifierToken = _verifierToken;
         app = _app;
+        verificationHash = _verificationHash;
     }
 
     /**
@@ -37,6 +39,15 @@ contract BrightID is Ownable, IBrightID {
         emit AppSet(_app);
     }
 
+    /**
+     * @notice Set verification hash
+     * @param _verificationHash sha256 of the verification expression
+     */
+    function setVerificationHash(bytes32 _verificationHash) public onlyOwner {
+        verificationHash = _verificationHash;
+        emit VerificationHashSet(_verificationHash);
+    }
+
     /**
      * @notice Set verifier token
      * @param _verifierToken verifier token
@@ -48,34 +59,26 @@ contract BrightID is Ownable, IBrightID {
 
     /**
      * @notice Register a user by BrightID verification
-     * @param addrs The history of addresses used by this user in the app
+     * @param addr The address used by this user in the app
      * @param timestamp The BrightID node's verification timestamp
      * @param v Component of signature
      * @param r Component of signature
      * @param s Component of signature
      */
     function verify(
-        address[] memory addrs,
+        address addr,
         uint timestamp,
         uint8 v,
         bytes32 r,
         bytes32 s
     ) public {
-        require(verifications[addrs[0]].time < timestamp, "newer verification registered before");
-
-        bytes32 message = keccak256(abi.encodePacked(app, addrs, timestamp));
+        bytes32 message = keccak256(abi.encodePacked(app, addr, verificationHash, timestamp));
         address signer = ecrecover(message, v, r, s);
         require(verifierToken.balanceOf(signer) > 0, "not authorized");
 
-        verifications[addrs[0]].time = timestamp;
-        verifications[addrs[0]].isVerified = true;
-        for(uint i = 1; i < addrs.length; i++) {
-            verifications[addrs[i]].time = timestamp;
-            verifications[addrs[i]].isVerified = false;
-            history[addrs[i - 1]] = addrs[i];
-        }
-        history[addrs[i-1]] = address(0);
-        emit Verified(addrs[0]);
+        verifications[addr].time = timestamp;
+        verifications[addr].isVerified = true;
+        emit Verified(addr);
     }
 
     /**
diff --git a/IBrightID.sol b/IBrightID.sol
index acf90e7..fa82fc7 100644
--- a/IBrightID.sol
+++ b/IBrightID.sol
@@ -3,5 +3,4 @@ pragma solidity ^0.6.3;
 interface IBrightID {
     event Verified(address indexed addr);
     function isVerified(address addr) external view returns (bool);
-    function history(address addr) external view returns (address);
 }
diff --git a/StoppableBrightID.sol b/StoppableBrightID.sol
index 136c73c..2fe1c93 100644
--- a/StoppableBrightID.sol
+++ b/StoppableBrightID.sol
@@ -8,6 +8,7 @@ contract StoppableBrightID is Ownable, IBrightID {
     IERC20 public supervisorToken;
     IERC20 public proposerToken;
     bytes32 public app;
+    bytes32 public verificationHash;
 
     event Verified(address indexed addr);
     event Proposed(address indexed addr);
@@ -16,6 +17,7 @@ contract StoppableBrightID is Ownable, IBrightID {
     event TimingSet(uint waiting, uint timeout);
     event MembershipTokensSet(IERC20 supervisorToken, IERC20 proposerToken);
     event AppSet(bytes32 _app);
+    event VerificationHashSet(bytes32 verificationHash);
 
     bool public stopped = false;
     uint public waiting;
@@ -27,7 +29,6 @@ contract StoppableBrightID is Ownable, IBrightID {
     }
     mapping(address => Verification) public verifications;
     mapping(bytes32 => uint) public proposals;
-    mapping(address => address) override public history;
 
     /**
      * @param _supervisorToken supervisor ERC20 token
@@ -35,19 +36,22 @@ contract StoppableBrightID is Ownable, IBrightID {
      * @param _app BrightID app used for verifying users
      * @param _waiting The waiting amount in block number
      * @param _timeout The timeout amount in block number
+     * @param _verificationHash sha256 of the verification expression
      */
     constructor(
         IERC20 _supervisorToken,
         IERC20 _proposerToken,
         bytes32 _app,
         uint _waiting,
-        uint _timeout
+        uint _timeout,
+        bytes32 _verificationHash
     ) public {
         supervisorToken = _supervisorToken;
         proposerToken = _proposerToken;
         app = _app;
         waiting = _waiting;
         timeout = _timeout;
+        verificationHash = _verificationHash;
     }
 
     /**
@@ -59,6 +63,15 @@ contract StoppableBrightID is Ownable, IBrightID {
         emit AppSet(_app);
     }
 
+    /**
+     * @notice Set verification hash
+     * @param _verificationHash sha256 of the verification expression
+     */
+    function setVerificationHash(bytes32 _verificationHash) public onlyOwner {
+        verificationHash = _verificationHash;
+        emit VerificationHashSet(_verificationHash);
+    }
+
     /**
      * @notice Set supervisor and proposer Tokens
      * @param _supervisorToken supervisor ERC20 token
@@ -100,14 +113,14 @@ contract StoppableBrightID is Ownable, IBrightID {
 
     /**
      * @notice Propose a registration
-     * @param addrs The history of addresses used by this user in the app
+     * @param addr The address used by this user in the app
      * @param timestamp The BrightID node's verification timestamp
      * @param v Component of signature
      * @param r Component of signature
      * @param s Component of signature
      */
     function propose(
-        address[] memory addrs,
+        address addr,
         uint timestamp,
         uint8 v,
         bytes32 r,
@@ -115,41 +128,34 @@ contract StoppableBrightID is Ownable, IBrightID {
     ) public {
         require(!stopped, "contract is stopped");
 
-        bytes32 message = keccak256(abi.encodePacked(app, addrs, timestamp));
+        bytes32 message = keccak256(abi.encodePacked(app, addr, verificationHash, timestamp));
         address signer = ecrecover(message, v, r, s);
         require(proposerToken.balanceOf(signer) > 0, "not authorized");
 
         proposals[message] = block.number;
-        emit Proposed(addrs[0]);
+        emit Proposed(addr);
     }
 
     /**
      * @notice Verify a registration
-     * @param addrs The history of addresses used by this user in the app
+     * @param addr The address used by this user in the app
      * @param timestamp The BrightID node's verification timestamp
      */
     function verify(
-        address[] memory addrs,
+        address addr,
         uint timestamp
     ) public {
         require(!stopped, "contract is stopped");
-        require(verifications[addrs[0]].time < timestamp, "newer verification registered before");
 
-        bytes32 message = keccak256(abi.encodePacked(app, addrs, timestamp));
+        bytes32 message = keccak256(abi.encodePacked(app, addr, verificationHash, timestamp));
         uint pblock = proposals[message];
         require(pblock > 0, "not proposed");
         require(block.number - pblock > waiting, "proposal is waiting");
         require(block.number - pblock < timeout, "proposal timed out");
 
-        verifications[addrs[0]].time = timestamp;
-        verifications[addrs[0]].isVerified = true;
-        for(uint i = 1; i < addrs.length; i++) {
-            verifications[addrs[i]].time = timestamp;
-            verifications[addrs[i]].isVerified = false;
-            history[addrs[i - 1]] = addrs[i];
-        }
-        history[addrs[i-1]] = address(0);
-        emit Verified(addrs[0]);
+        verifications[addr].time = timestamp;
+        verifications[addr].isVerified = true;
+        emit Verified(addr);
     }
 
     /**