Ciphers work on a fixed size length. So when we use depth, we encrypt blocks of 64 bits, when we use as we encrypt blocks have 128 bits. But as we all know, it is hardly that we have files in that size. We have fines waiting in megabytes and gigabytes. So what do we do? Do we break the file apart into blocks and encrypt each one.

At the end, we joined the parts together, that is the block cipher mode of operation. And there are several of them. Some are hardly used, and others are used everywhere. And if the last block of our file is less than 64 bits, or 128 bits, assuming we're using depth or a yes, we fill out the remainder with what is called a padding. This could be a predefined value as all ones or all zeros. The first block cipher mode of operation is ECB, electronic codebook.

In ECB, which is rarely used, we encrypt our file, block after block, each according to its algorithm. And in the end, we join them together. It is the easiest block cipher mode of operation, but it is also the less secure of all Why? Well, because there is a direct linkage between the cipher text and the plain text Over time, crypto analyst could find patterns that are occurring. Remember, the same key is used to encrypt the different blocks. And if we wish to decrypt the cipher file, we split it into 64 bits and use the same key to decrypted.

Repetitions of the same block cipher can happen through our the cipher text.