encrypt a file on iphone-sdk

Question

I'd like to have a file encryption functionality for my iphone application. For desktop based applications i used the function below to encrypt relatively small files:

- (NSData *)aesEncrypt:(NSString *)key {
 // 'key' should be 32 bytes for AES256, will be null-padded otherwise
 char keyPtr[kCCKeySizeAES256+1]; // room for terminator (unused)
 bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)

 // fetch key data
 [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

 NSUInteger dataLength = [self length];

 //See the doc: For block ciphers, the output size will always be less than or 
 //equal to the input size plus the size of one block.
 //That's why we need to add the size of one block here
 size_t bufferSize = dataLength + kCCBlockSizeAES128;
 void *buffer = malloc(bufferSize);

 size_t numBytesEncrypted = 0;



 CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
            keyPtr, kCCKeySizeAES256,
            NULL /* initialization vector (optional) */,
            [self bytes], dataLength, /* input */
            buffer, bufferSize, /* output */
            &numBytesEncrypted);
 if (cryptStatus == kCCSuccess) {
  //the returned NSData takes ownership of the buffer and will free it on deallocation
  return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
 }

 free(buffer); //free the buffer;
 return nil;
}

But i don't think this code can be used on an iphone. If i try to encrypt a 5mb file it will take up at least 10 mb in ram, since it will be loaded to NSData and returned as such. Is there a method that would eccrypt a file by reading small blocks and writing output to another file? Or am i wrong about this taking so m

Answer 1

Try RNCryptor https://github.com/rnapier/RNCryptor

I've used this successfully in my app.