c# - Sequential .NET DESCryptoServiceProvider encryption and decryption produces wrong bytes after 96th -

basically, here code:

        des des = new descryptoserviceprovider();         passwordderivebytes pdb = new passwordderivebytes(new byte[]{123}, new byte[0]);         des.iv = new byte[8];         des.key = pdb.cryptderivekey("des", "md5", 0, des.iv);          byte[] = enumerable.range(1, 100).select(i => (byte)i).concat(new byte[4]).toarray();         byte[] b = new byte[a.length];         byte[] c = new byte[a.length];          using (var encryptor = des.createencryptor())             encryptor.transformblock(a, 0, a.length, b, 0);          using (var decryptor = des.createdecryptor())             decryptor.transformblock(b, 0, b.length, c, 0);          (int = 0; < a.length; i++)             if (a[i] != c[i])                 debugger.break(); 

it breaks @ i == 96. why?

another small question: omitting of .concat(new byte[4]) causes first transformblock throw argumentexception. why can't encrypt array of sorted bytes without 4 zeroes @ end?

des block cypher of 64bit blocks, therefore data encoded needs multiple of 64bit blocks. (see http://en.wikipedia.org/wiki/data_encryption_standard)

looking @ 96, assume last block different based on fact padding 100 (not 64bit block) 104 (64bit block) not setting values of last 4 bytes 0.

hope helps,