Encrypt file on iphone-sdk

Question

I would like to have a file encryption function for my iphone application. For desktop applications, I used the following function 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 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 do not think that this code can be used on iphone. If I try to encrypt a 5 MB file, it will occupy at least 10 MB in memory, as it will be loaded into 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 mistaken in this, taking so m

Answer 1

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

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