Delete multichunk from cache if decryption failed. Related to #59

syncany-lib/src/main/java/org/syncany/operations/Downloader.java

@@ -70,17 +70,31 @@ public void downloadAndDecryptMultiChunks(Set<MultiChunkId> unknownMultiChunkIds
 				logger.log(Level.INFO, "  + Downloading multichunk " + multiChunkId + " ...");
 				transferManager.download(remoteMultiChunkFile, localEncryptedMultiChunkFile);
 
-				logger.log(Level.INFO, "  + Decrypting multichunk " + multiChunkId + " ...");
-				InputStream multiChunkInputStream = config.getTransformer().createInputStream(new FileInputStream(localEncryptedMultiChunkFile));
-				OutputStream decryptedMultiChunkOutputStream = new FileOutputStream(localDecryptedMultiChunkFile);
+				try {
+					logger.log(Level.INFO, "  + Decrypting multichunk " + multiChunkId + " ...");
+					InputStream multiChunkInputStream = config.getTransformer().createInputStream(new FileInputStream(localEncryptedMultiChunkFile));
+					OutputStream decryptedMultiChunkOutputStream = new FileOutputStream(localDecryptedMultiChunkFile);
+
+					IOUtils.copy(multiChunkInputStream, decryptedMultiChunkOutputStream);
+
+					decryptedMultiChunkOutputStream.close();
+					multiChunkInputStream.close();
 
-				IOUtils.copy(multiChunkInputStream, decryptedMultiChunkOutputStream);
-
-				decryptedMultiChunkOutputStream.close();
-				multiChunkInputStream.close();
-
-				logger.log(Level.FINE, "  + Locally deleting multichunk " + multiChunkId + " ...");
-				localEncryptedMultiChunkFile.delete();
+				}
+				catch (IOException e) {
+					// Security: Deleting the multichunk if the decryption/extraction failed is important!
+					//           If it is not deleted, the partially decrypted multichunk will reside in the
+					//           local cache and the next 'down' will try to use it. If this is the only
+					//           multichunk that has been tampered with, other changes might be applied to the 
+					//           file system! See https://github.com/syncany/syncany/issues/59#issuecomment-55154793
+
+					logger.log(Level.FINE, "    -> FAILED: Decryption/extraction of multichunk failed, deleting " + multiChunkId + " ...");
+					localDecryptedMultiChunkFile.delete();
+				}
+				finally {
+					logger.log(Level.FINE, "  + Locally deleting multichunk " + multiChunkId + " ...");
+					localEncryptedMultiChunkFile.delete();
+				}
 			}
 		}