added killswitch for credential generation

contracts/basic-bandwidth-generation/contracts/BandwidthGenerator.sol

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: Apache-2.0
 pragma solidity 0.8.10;
 
 import "./CosmosToken.sol";
@@ -9,10 +10,11 @@ import "@openzeppelin/contracts/utils/math/SafeMath.sol";
  * @title BandwidthGenerator
  * @dev   Contract for generating Basic Bandwidth Credentials (BBCs) on the Nym cosmos blockchain, 
  *        using ERC20 representations of NYM as payment. Utilises the Gravity Bridge for cross-chain payment. 
+ * 
+ *        Credential generation can be switched on/off by the contract owner.
  *        
  *        Credentials represent a certain amount of bandwidth which can be sent through the Nym Mixnet. 
  *        By default 1 NYM = 1 GB of bandwidth. The `BytesPerToken` amount can be adjusted by the contract owner. 
- * 
  *        The amount of bandwidth bought is calculated according to the following formula: 
  *        `(Token amount in 'wei' / 10**18) * BytesPerToken`
  */ 
@@ -23,6 +25,7 @@ contract BandwidthGenerator is Ownable {
     CosmosERC20 public erc20;
     Gravity     public gravityBridge; 
     uint256     public BytesPerToken; 
+    bool        public credentialGenerationEnabled;
     
     event BBCredentialPurchased(
         uint256 Bandwidth,
@@ -34,7 +37,16 @@ contract BandwidthGenerator is Ownable {
     event RatioChanged(
         uint256 indexed NewBytesPerToken
     );
-    
+
+    event CredentialGenerationSwitch(
+        bool Enabled
+    ); 
+
+    modifier checkEnabled() {
+        require(credentialGenerationEnabled, "BandwidthGenerator: credential generation isn't currently enabled");
+        _;
+    }
+
     /**
      * @param _erc20          Address of the erc20NYM deployed through the Gravity Bridge.
      * @param _gravityBridge  Address of the deployed Gravity Bridge. 
@@ -45,6 +57,7 @@ contract BandwidthGenerator is Ownable {
         erc20 = _erc20;
         gravityBridge = _gravityBridge; 
         BytesPerToken = 1073741824; // default amount set at deployment: 1 erc20NYM = 1073741824 Bytes = 1GB
+        credentialGenerationEnabled = true;
     }
 
     /**
@@ -56,6 +69,15 @@ contract BandwidthGenerator is Ownable {
         BytesPerToken = _newBytesPerTokenAmount;  
         emit RatioChanged(_newBytesPerTokenAmount);
     }
+
+    /**
+     * @dev                            Switches credential generation on/off. Can only be called by Owner. 
+     * @param _generation              Whether credential generation is turned on/off. 
+     */  
+    function credentialGenerationSwitch(bool _generation) public onlyOwner {
+        credentialGenerationEnabled = _generation; 
+        emit CredentialGenerationSwitch(_generation); 
+    }
     
     /**
      * @dev                           Function to create a BBC for account owning the verification key on the Nym Cosmos Blockchain
@@ -65,7 +87,7 @@ contract BandwidthGenerator is Ownable {
      * @param _signedVerificationKey  Number of erc20NYMs to spend signed by _verificationKey for auth on Cosmos Blockchain.
      * @param _cosmosRecipient        Address of the recipient of payment on Nym Cosmos Blockchain.
      */    
-    function generateBasicBandwidthCredential(uint256 _amount, uint256 _verificationKey, bytes memory _signedVerificationKey, string calldata _cosmosRecipient) public {
+    function generateBasicBandwidthCredential(uint256 _amount, uint256 _verificationKey, bytes memory _signedVerificationKey, string calldata _cosmosRecipient) public checkEnabled {
         require(_signedVerificationKey.length == 64, "BandwidthGenerator: Signature doesn't have 64 bytes");
         erc20.transferFrom(msg.sender, address(this), _amount);
         erc20.approve(address(gravityBridge), _amount);