While writing software dealing with cryptography, it’s important to be familiar with a concept of block cipher modes. Most of common encryption algorithms work on data grouped together into blocks. For instance, in case of DES cipher, the block size is equal to 64 bits. While encrypting larger amounts of data, cipher implementation will divide the input into 8 byte chunks and encrypt each of them separately.
This is definitely not desired – in case of specific input that contains repeatable sets of information (like text documents, bitmaps with large areas of the same color), the encrypted chunks might repeat just like original plain-text values do. As a result of that, encrypted data might reveal important details of the original content.
