Final answer:
When the data to be encrypted is not big enough to fill the block in block ciphers, padding is usually applied to fill the remaining space. Different padding schemes can be used, such as PKCS#7 or ANSI X9.23. Padding needs to be removed during the decryption process.
Step-by-step explanation:
When the data to be encrypted is not big enough to fill the block in block ciphers, padding is usually applied to fill the remaining space. Padding adds extra bits or characters to the data so that it completely fills the block size. There are different padding schemes that can be used, such as PKCS#7 or ANSI X9.23, and the choice depends on the specific encryption algorithm being used.
For example, if we have a block cipher with a block size of 64 bits (8 bytes) and the data to be encrypted is only 5 bytes long, we need to add 3 bytes of padding. The padding could be any 3 bytes, such as 0x00 0x00 0x03, to indicate that 3 bytes were added.
It's important to note that the padding needs to be removed during the decryption process, so the recipient knows which bytes were added and which were part of the original data.