Proper error handling for outdated vault formats

main/crypto-api/src/main/java/org/cryptomator/crypto/AbstractCryptorDecorator.java

@@ -13,6 +13,7 @@ import org.cryptomator.crypto.exceptions.DecryptFailedException;
 import org.cryptomator.crypto.exceptions.EncryptFailedException;
 import org.cryptomator.crypto.exceptions.MacAuthenticationFailedException;
 import org.cryptomator.crypto.exceptions.UnsupportedKeyLengthException;
+import org.cryptomator.crypto.exceptions.UnsupportedVaultException;
 import org.cryptomator.crypto.exceptions.WrongPasswordException;
 
 public class AbstractCryptorDecorator implements Cryptor {
@@ -29,7 +30,7 @@ public class AbstractCryptorDecorator implements Cryptor {
 	}
 
 	@Override
-	public void decryptMasterKey(InputStream in, CharSequence password) throws DecryptFailedException, WrongPasswordException, UnsupportedKeyLengthException, IOException {
+	public void decryptMasterKey(InputStream in, CharSequence password) throws DecryptFailedException, WrongPasswordException, UnsupportedKeyLengthException, IOException, UnsupportedVaultException {
 		cryptor.decryptMasterKey(in, password);
 	}
 

main/crypto-api/src/main/java/org/cryptomator/crypto/Cryptor.java

@@ -21,6 +21,7 @@ import org.cryptomator.crypto.exceptions.DecryptFailedException;
 import org.cryptomator.crypto.exceptions.EncryptFailedException;
 import org.cryptomator.crypto.exceptions.MacAuthenticationFailedException;
 import org.cryptomator.crypto.exceptions.UnsupportedKeyLengthException;
+import org.cryptomator.crypto.exceptions.UnsupportedVaultException;
 import org.cryptomator.crypto.exceptions.WrongPasswordException;
 
 /**
@@ -39,8 +40,9 @@ public interface Cryptor extends Destroyable {
 	 * @throws DecryptFailedException If the decryption failed for various reasons (including wrong password).
 	 * @throws WrongPasswordException If the provided password was wrong. Note: Sometimes the algorithm itself fails due to a wrong password. In this case a DecryptFailedException will be thrown.
 	 * @throws UnsupportedKeyLengthException If the masterkey has been encrypted with a higher key length than supported by the system. In this case Java JCE needs to be installed.
+	 * @throws UnsupportedVaultException If the masterkey file is too old or too modern.
 	 */
-	void decryptMasterKey(InputStream in, CharSequence password) throws DecryptFailedException, WrongPasswordException, UnsupportedKeyLengthException, IOException;
+	void decryptMasterKey(InputStream in, CharSequence password) throws DecryptFailedException, WrongPasswordException, UnsupportedKeyLengthException, IOException, UnsupportedVaultException;
 
 	/**
 	 * Encrypts a given plaintext path representing a directory structure. See {@link #encryptFilename(String, CryptorMetadataSupport)} for contents inside directories.

main/crypto-api/src/main/java/org/cryptomator/crypto/exceptions/UnsupportedVaultException.java

@@ -0,0 +1,32 @@
+package org.cryptomator.crypto.exceptions;
+
+public class UnsupportedVaultException extends Exception {
+
+	private static final long serialVersionUID = -5147549533387945622L;
+
+	private final Integer detectedVersion;
+	private final Integer supportedVersion;
+
+	public UnsupportedVaultException(Integer detectedVersion, Integer supportedVersion) {
+		super("Tried to open vault of version " + detectedVersion + ", but can only handle version " + supportedVersion);
+		this.detectedVersion = detectedVersion;
+		this.supportedVersion = supportedVersion;
+	}
+
+	public Integer getDetectedVersion() {
+		return detectedVersion;
+	}
+
+	public Integer getSupportedVersion() {
+		return supportedVersion;
+	}
+
+	public boolean isVaultOlderThanSoftware() {
+		return detectedVersion == null || detectedVersion < supportedVersion;
+	}
+
+	public boolean isSoftwareOlderThanVault() {
+		return detectedVersion > supportedVersion;
+	}
+
+}