The message is saying it tried to decode the hex into binary data and the length it was expecting didn’t match so check you’ve entered your hex string correctly. You might have missed a character off or there are hidden white spaces lurking somewhere.

Hi Simon, be careful here. Don’t forget that block size and key size are different. Your assumption that the block size of AES256 is 32 is wrong. The AES algorithm uses a 16-byte block size (which is 128-bit assuming 8 bits in a byte). This block size is the same for all key sizes. In laymen terms, the block size is how thinly the data gets chopped up to be worked with; the key size is how often it rotates or gets “shuffled”. The IV is used to modify the first data block so that is why it must match.

Typically for AES the IV is the size of a block so the IV is 128-bits long.

My solution does actually follow the `CCrypt` snippet you posted – if you look at the IVs you’ll see they are 32 character hexadecimal strings, 16 pairs – each hex letter pair represents 8-bits each so (8 x 16 = 128-bit).

Hope that helps.

Yes, this is a bug. Good find, I knew someone would find it soon! ;-)

`bzero` replaces everything at the given memory address with zeros. My intention was to “zero out” the memory before copying the data from the NSData object resulting in at least one byte at the end being \0 (\0 is used by C to indicate a string is complete).

However just doing what Boris suggests won’t work on its own because we need the length of data + 1 for the \0 character. We’re actually initialising the pointer with one less byte of data than we should do. Hence the fix that will solve both warnings in Xcode is:

    NSData *data = [NSData dataFromHexString:hexString];
    NSAssert((data.length + 1) == length, @"The hex provided didn't decode to match length");
    
    unsigned long total_bytes = (length + 1) * sizeof(char);
    
    *dataPtr = malloc(total_bytes);
    bzero(*dataPtr, total_bytes);
    memcpy(*dataPtr, data.bytes, data.length);

Hope that helps.

Boris,

bzero(*dataPtr, sizeof(*dataPtr));

XCode 9 hates this line. I keep getting memory errors if I use the category multiple times.
‘bzero’ call operates on objects of type ‘char’ while the size is based on a different type ‘char *’

Symbiosis(8772,0x10d2d1340) malloc: *** error for object 0x608000457af0: Invalid pointer dequeued from free list
*** set a breakpoint in malloc_error_break to debug

The strange thing is my encryption and decryption is working before the memory crash.

I have implemented the same but the IV is not prefixing to encrypted data. Could you please help me

In the NSData docs under Discussion it says [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted] takes ownership of the bytes pointer and frees it on deallocation. Hence it only needs to be freed if the cryptStatus fails.

In other words once we wrap the bytes up in NSData we can let the system free it. Hope that helps!