Allow anyone to register a signer attestation

contracts/src/SystemConfigGlobal.sol

@@ -52,13 +52,15 @@ contract SystemConfigGlobal is OwnableUpgradeable, ISemver, NitroValidator {
         delete validPCR0s[keccak256(pcr0)];
     }
 
-    function registerSigner(bytes calldata attestationTbs, bytes calldata signature) external onlyOwner {
+    function registerSigner(bytes calldata attestationTbs, bytes calldata signature) external {
         Ptrs memory ptrs = validateAttestation(attestationTbs, signature);
         bytes32 pcr0 = attestationTbs.keccak(ptrs.pcrs[0]);
         require(validPCR0s[pcr0], "invalid pcr0 in attestation");
 
         require(ptrs.timestamp + MAX_AGE > block.timestamp, "attestation too old");
 
+        // The publicKey is encoded in the form specified in section 4.3.6 of ANSI X9.62, which is a
+        // 0x04 byte followed by the x and y coordinates of the public key. We ignore the first byte.
         bytes32 publicKeyHash = attestationTbs.keccak(ptrs.publicKey.start() + 1, ptrs.publicKey.length() - 1);
         address enclaveAddress = address(uint160(uint256(publicKeyHash)));
         validSigners[enclaveAddress] = true;