on-the-fly MAC calculation for better performance (addresses issue #38)

we still need to add some kind of warning on the UI and create an async MAC checker for ranged requests

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

@@ -79,7 +79,7 @@ public interface Cryptor extends SensitiveDataSwipeListener {
 	 * @return Number of decrypted bytes. This might not be equal to the encrypted file size due to optional metadata written to it.
 	 * @throws DecryptFailedException If decryption failed
 	 */
-	Long decryptedFile(SeekableByteChannel encryptedFile, OutputStream plaintextFile) throws IOException, DecryptFailedException;
+	Long decryptFile(SeekableByteChannel encryptedFile, OutputStream plaintextFile) throws IOException, DecryptFailedException;
 
 	/**
 	 * @param pos First byte (inclusive)

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

@@ -82,9 +82,9 @@ public class SamplingDecorator implements Cryptor, CryptorIOSampling {
 	}
 
 	@Override
-	public Long decryptedFile(SeekableByteChannel encryptedFile, OutputStream plaintextFile) throws IOException, DecryptFailedException {
+	public Long decryptFile(SeekableByteChannel encryptedFile, OutputStream plaintextFile) throws IOException, DecryptFailedException {
 		final OutputStream countingInputStream = new CountingOutputStream(decryptedBytes, plaintextFile);
-		return cryptor.decryptedFile(encryptedFile, countingInputStream);
+		return cryptor.decryptFile(encryptedFile, countingInputStream);
 	}
 
 	@Override

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

@@ -0,0 +1,11 @@
+package org.cryptomator.crypto.exceptions;
+
+public class MacAuthenticationFailedException extends DecryptFailedException {
+
+	private static final long serialVersionUID = -5577052361643658772L;
+
+	public MacAuthenticationFailedException(String msg) {
+		super(msg);
+	}
+
+}