带录音的iOS-RNCryptor

Question

I'm new to encryption and am trying to encrypt recordings with RNCryptor. The files are encrypted properly but, after decrypting, the created NSData causes the AVAudioPlayer to fail initialization. The method I'm using for the encryption and decryption are...

- (void)renameFileInDocumentsFolder:(NSString *)oldFilename withNewName:(NSString *)newFilename
{

 NSFileManager *filemgr;

NSString *oldPath = [self getFilePathFromDocumentsFolder:oldFilename];
filemgr = [NSFileManager defaultManager];
NSData *data = [filemgr contentsAtPath:oldPath];

 NSString *destPath = [[oldPath stringByDeletingLastPathComponent] stringByAppendingPathComponent:[newFilename stringByAppendingString:@".m4a"]];
NSLog(@"DEST:%@", destPath);

NSError *error;

NSData *encryptedData = [RNEncryptor encryptData:data
                                    withSettings:kRNCryptorAES256Settings
                                        password:@"ABC123"
                                           error:&error];



[encryptedData writeToFile:destPath atomically:YES];
[filemgr removeItemAtPath:oldPath error:&error];


}

-(NSData *)decryptFilePathFromDocumentsFolder:(NSString *)filename
{
AudioRecorderAppDelegate *appDelegate=[AudioRecorderAppDelegate sharedDelegate];
_cacheDirectory = [[[appDelegate applicationCacheDirectory]path]stringByAppendingPathComponent:@"Recordings"];
   // NSFileManager *fileManager = [NSFileManager defaultManager];
NSError *error;

NSString *filePath = [_cacheDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.m4a", filename]];
  NSData *data = [NSData dataWithContentsOfFile:filePath];

NSData *decData = [RNDecryptor decryptData:data withPassword:@"ABC123"   error:&error];



return decData;
}

The AVAudioPlayer initialization is... - (void)initializeAudioPlayer {

NSData *recording = [self decryptFilePathFromDocumentsFolder:_fileNameTextField.text];

if(!audioPlayer)
{
    NSError *error=nil;

    audioPlayer = [[AVAudioPlayer alloc]
                   initWithData:recording fileTypeHint:@".m4a" error:&error];
    if (error)

        NSLog(@"Error: %@", [error localizedDescription]);
    else

I don't know what I'm doing wrong or if RNCryptor is even meant to encrypt audio files but any help would be greatly appreciated.

Answer 1

There are lots of places where you're not checking errors, both in the cryptor calls, and in the reading and writing of the file. Make sure at each point that you actually have what you expect. Make sure the written and returned data are of reasonable sizes (about the same as the original file). Make sure the original file actually is playable. Makes sure after decryption you have precisely the same bytes as you started with.

RNCryptor doesn't care what it encrypts. But if you're doing this on the UI thread (which it looks like you're doing, reading a large file from disk can cause you're program to hang, in some cases long enough for the OS to kill you. Generally large file operations (like large audio files) need to be done asynchronously.