Simplify

Signed-off-by: alperozturk <alper_ozturk@proton.me>

app/src/main/java/com/owncloud/android/operations/DownloadFileOperation.java

@@ -264,19 +264,10 @@ public class DownloadFileOperation extends RemoteOperation {
 
                 byte[] key = decodeStringToBase64Bytes(keyString);
                 byte[] iv = decodeStringToBase64Bytes(nonceString);
-                byte[] authenticationTag = decodeStringToBase64Bytes(authenticationTagString);
 
                 try {
                     Cipher cipher = EncryptionUtils.getCipher(Cipher.DECRYPT_MODE, key, iv);
-                    byte[] decryptedBytes = EncryptionUtils.decryptFile(cipher,
-                                                                        tmpFile,
-                                                                        authenticationTag,
-                                                                        new ArbitraryDataProviderImpl(operationContext),
-                                                                        user);
-
-                    try (FileOutputStream fileOutputStream = new FileOutputStream(tmpFile)) {
-                        fileOutputStream.write(decryptedBytes);
-                    }
+                    tmpFile = EncryptionUtils.decryptFile(tmpFile, authenticationTagString, cipher, new ArbitraryDataProviderImpl(operationContext), user);
                 } catch (Exception e) {
                     return new RemoteOperationResult(e);
                 }

app/src/main/java/com/owncloud/android/operations/UploadFileOperation.java

@@ -560,16 +560,10 @@ public class UploadFileOperation extends SyncOperation {
             Long creationTimestamp = FileUtil.getCreationTimestamp(originalFile);
 
             /***** E2E *****/
-
-            // Key, always generate new one
             byte[] key = EncryptionUtils.generateKey();
-
-            // IV, always generate new one
             byte[] iv = EncryptionUtils.randomBytes(EncryptionUtils.ivLength);
-
             Cipher cipher = EncryptionUtils.getCipher(Cipher.ENCRYPT_MODE, key, iv);
             File file = new File(mFile.getStoragePath());
-
             EncryptedFile encryptedFile = EncryptionUtils.encryptFile(file, cipher);
 
             // new random file name, check if it exists in metadata

app/src/main/java/com/owncloud/android/utils/EncryptionUtils.java

@@ -114,6 +114,7 @@ import java.util.UUID;
 
 import javax.crypto.BadPaddingException;
 import javax.crypto.Cipher;
+import javax.crypto.CipherInputStream;
 import javax.crypto.CipherOutputStream;
 import javax.crypto.IllegalBlockSizeException;
 import javax.crypto.KeyGenerator;
@@ -563,9 +564,6 @@ public final class EncryptionUtils {
         return Base64.decode(string, Base64.NO_WRAP);
     }
 
-    /*
-    ENCRYPTION
-     */
     public static EncryptedFile encryptFile(File file, Cipher cipher) throws IOException, InvalidParameterSpecException {
         File encryptedFile = new File(file.getAbsolutePath() + ".enc");
         encryptFileWithGivenCipher(file, encryptedFile, cipher);
@@ -602,7 +600,37 @@ public final class EncryptionUtils {
         inputStream.close();
     }
 
+    public static File decryptFile(File encryptedFile,
+                                   String authenticationTag,
+                                   Cipher cipher,
+                                   ArbitraryDataProvider arbitraryDataProvider,
+                                   User user) throws InvalidParameterSpecException {
+        File decryptedFile = new File(encryptedFile.getAbsolutePath().replace(".enc", "_decrypted"));
+
+        try (FileInputStream inputStream = new FileInputStream(encryptedFile);
+             FileOutputStream fileOutputStream = new FileOutputStream(decryptedFile);
+             CipherInputStream cipherInputStream = new CipherInputStream(inputStream, cipher)) {
+
+            byte[] buffer = new byte[4096];
+            int bytesRead;
+
+            while ((bytesRead = cipherInputStream.read(buffer)) != -1) {
+                fileOutputStream.write(buffer, 0, bytesRead);
+            }
+        } catch (Exception e) {
+            Log_OC.d(TAG, "Error caught at decryptFile(): " + e.getLocalizedMessage());
+        }
+
+        if (!getAuthenticationTag(cipher).equals(authenticationTag)) {
+            reportE2eError(arbitraryDataProvider, user);
+            throw new SecurityException("Tag not correct");
+        }
+
+        return decryptedFile;
+    }
+
     // FIXME Decryption is broken
+    /*
     public static byte[] decryptFile(
                                     Cipher cipher,
                                     File file,
@@ -627,6 +655,8 @@ public final class EncryptionUtils {
 
         return cipher.doFinal(fileBytes);
     }
+     */
+
 
     /**
      * Encrypt string with RSA algorithm, ECB mode, OAEPWithSHA-256AndMGF1 padding Asymmetric encryption, with private