diff --git a/contracts/Errors.sol b/contracts/Errors.sol
new file mode 100644
index 0000000..7c40b2c
--- /dev/null
+++ b/contracts/Errors.sol
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.9;
+
+interface ISFCErrors {
+    error TransfersNotAllowed();
+
+    // pubkeys
+    error PubkeyExists();
+    error NotMainNet();
+    error MalformedPubkey();
+    error NotLegacyValidator();
+    error ValidatorDoesNotExist();
+    error SamePubkey();
+    error PubkeyAllowedOnlyOnce();
+
+    // redirections
+    error SameRedirectionAuthorizer();
+    error NotAuthorized();
+    error AlreadyCompleted();
+    error SameAddress();
+    error ZeroAddress();
+    error NoRequest();
+}
\ No newline at end of file
diff --git a/contracts/ownership/Ownable.sol b/contracts/ownership/Ownable.sol
index 65537ea..2efd354 100644
--- a/contracts/ownership/Ownable.sol
+++ b/contracts/ownership/Ownable.sol
@@ -2,6 +2,8 @@
 pragma solidity ^0.8.9;
 
 import {Initializable} from "../common/Initializable.sol";
+import {ZeroAddress} from "../Errors.sol";
+
 /**
  * @dev Contract module which provides a basic access control mechanism, where
  * there is an account (an owner) that can be granted exclusive access to
@@ -19,11 +21,6 @@ contract Ownable is Initializable {
      */
     error NotOwner();
 
-    /**
-     * @dev Given zero address.
-     */
-    error ZeroAddress();
-
     event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
 
     /**
diff --git a/contracts/sfc/SFC.sol b/contracts/sfc/SFC.sol
index a063d56..51a5465 100644
--- a/contracts/sfc/SFC.sol
+++ b/contracts/sfc/SFC.sol
@@ -40,12 +40,14 @@ contract SFC is SFCBase, Version {
 
     // solhint-disable-next-line no-complex-fallback
     fallback() external payable {
-        require(msg.data.length != 0, "transfers not allowed");
+        if (msg.data.length == 0) {
+            revert TransfersNotAllowed();
+        }
         _delegate(libAddress);
     }
 
     receive() external payable {
-        revert("transfers not allowed");
+        revert TransfersNotAllowed();
     }
 
     /*
@@ -131,24 +133,38 @@ contract SFC is SFCBase, Version {
         for (uint256 vid = start; vid < end; vid++) {
             bytes memory pubkey = getValidatorPubkey[vid];
             if (pubkey.length > 0 && pubkeyHashToValidatorID[keccak256(pubkey)] != vid) {
-                require(pubkeyHashToValidatorID[keccak256(pubkey)] == 0, "already exists");
+                if (pubkeyHashToValidatorID[keccak256(pubkey)] != 0) {
+                    revert PubkeyExists();
+                }
                 pubkeyHashToValidatorID[keccak256(pubkey)] = vid;
             }
         }
     }
 
     function updateValidatorPubkey(bytes calldata pubkey) external {
-        require(getValidator[1].auth == 0x541E408443A592C38e01Bed0cB31f9De8c1322d0, "not mainnet");
-        require(pubkey.length == 66 && pubkey[0] == 0xc0, "malformed pubkey");
+        // TODO: Valid requirements?
+        if (getValidator[1].auth != 0x541E408443A592C38e01Bed0cB31f9De8c1322d0) {
+            revert NotMainNet();
+        }
+        if (pubkey.length != 66 || pubkey[0] != 0xc0) {
+            revert MalformedPubkey();
+        }
         uint256 validatorID = getValidatorID[msg.sender];
-        require(validatorID <= 59 || validatorID == 64, "not legacy validator");
-        require(_validatorExists(validatorID), "validator doesn't exist");
-        require(keccak256(pubkey) != keccak256(getValidatorPubkey[validatorID]), "same pubkey");
-        require(pubkeyHashToValidatorID[keccak256(pubkey)] == 0, "already used");
-        require(
-            validatorPubkeyChanges[validatorID] == 0 || validatorID == 64 || validatorID <= 12,
-            "allowed only once"
-        );
+        if (validatorID > 59 && validatorID != 64) {
+            revert NotLegacyValidator();
+        }
+        if (!_validatorExists(validatorID)) {
+            revert ValidatorDoesNotExist();
+        }
+        if (keccak256(pubkey) == keccak256(getValidatorPubkey[validatorID])) {
+            revert SamePubkey();
+        }
+        if (pubkeyHashToValidatorID[keccak256(pubkey)] != 0) {
+            revert PubkeyExists();
+        }
+        if (validatorPubkeyChanges[validatorID] != 0 && validatorID != 64 && validatorID > 12) {
+            revert PubkeyAllowedOnlyOnce();
+        }
 
         validatorPubkeyChanges[validatorID]++;
         pubkeyHashToValidatorID[keccak256(pubkey)] = validatorID;
@@ -157,7 +173,9 @@ contract SFC is SFCBase, Version {
     }
 
     function setRedirectionAuthorizer(address v) external onlyOwner {
-        require(redirectionAuthorizer != v, "same");
+        if (redirectionAuthorizer == v) {
+            revert SameRedirectionAuthorizer();
+        }
         redirectionAuthorizer = v;
     }
 
@@ -168,16 +186,26 @@ contract SFC is SFCBase, Version {
     }
 
     function initiateRedirection(address from, address to) external {
-        require(msg.sender == redirectionAuthorizer, "not authorized");
-        require(getRedirection[from] != to, "already complete");
-        require(from != to, "same address");
+        if (msg.sender != redirectionAuthorizer) {
+            revert NotAuthorized();
+        }
+        if (getRedirection[from] == to) {
+            revert AlreadyCompleted();
+        }
+        if (from == to) {
+            revert SameAddress();
+        }
         getRedirectionRequest[from] = to;
     }
 
     function redirect(address to) external {
         address from = msg.sender;
-        require(to != address(0), "zero address");
-        require(getRedirectionRequest[from] == to, "no request");
+        if (to == address(0)) {
+            revert ZeroAddress();
+        }
+        if (getRedirectionRequest[from] != to) {
+            revert NoRequest();
+        }
         getRedirection[from] = to;
         getRedirectionRequest[from] = address(0);
     }
diff --git a/contracts/sfc/SFCBase.sol b/contracts/sfc/SFCBase.sol
index d76acf1..0c4ada1 100644
--- a/contracts/sfc/SFCBase.sol
+++ b/contracts/sfc/SFCBase.sol
@@ -3,6 +3,7 @@ pragma solidity ^0.8.9;
 
 import {Decimal} from "../common/Decimal.sol";
 import {SFCState} from "./SFCState.sol";
+import "../Errors.sol";
 
 contract SFCBase is SFCState {
     uint256 internal constant OK_STATUS = 0;
diff --git a/contracts/test/UnitTestSFC.sol b/contracts/test/UnitTestSFC.sol
index e2306b4..0f15f35 100644
--- a/contracts/test/UnitTestSFC.sol
+++ b/contracts/test/UnitTestSFC.sol
@@ -5,6 +5,7 @@ import {Decimal} from "../common/Decimal.sol";
 import {SFC} from "../sfc/SFC.sol";
 import {SFCBase} from "../sfc/SFCBase.sol";
 import {SFCLib} from "../sfc/SFCLib.sol";
+import {ISFCErrors} from "../Errors.sol";
 import {NodeDriverAuth} from "../sfc/NodeDriverAuth.sol";
 import {NodeDriver} from "../sfc/NodeDriver.sol";
 import {UnitTestConstantsManager} from "./UnitTestConstantsManager.sol";
@@ -113,7 +114,7 @@ contract UnitTestNetworkInitializer {
     }
 }
 
-interface SFCUnitTestI {
+interface SFCUnitTestI is ISFCErrors {
     function currentSealedEpoch() external view returns (uint256);
 
     function getEpochSnapshot(
diff --git a/test/SFC.ts b/test/SFC.ts
index 201c88c..07bdd0e 100644
--- a/test/SFC.ts
+++ b/test/SFC.ts
@@ -52,7 +52,7 @@ describe('SFC', () => {
         to: this.sfc,
         value: 1,
       }),
-    ).to.revertedWith('transfers not allowed');
+    ).to.revertedWithCustomError(this.sfc, 'TransfersNotAllowed');
   });
 
   describe('Genesis validator', () => {