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In serial data transmission, every byte of data is padded with a ‘0’ in the beginning and one or two 1’s at the end of byte because
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- receiver is to be synchronized for byte reception
- receiver recovers lost 0s and 1s from these padded bits
- padded bits are useful in parity computation
- None of the above
- receiver is to be synchronized for byte reception
Correct Option: A
The primary use of padding is to prevent the cryptanalyst from using that predictability to find cribs that aid in breaking the encryption. Hence, padding bits are used to protect the bits. All the bytes that are required to be padded are padded with zero.
There are two types of padding methods: Bit padding/Byte padding and Zero padding.
Bit Padding : Two types of bits are used in the process: Single set bit generally represented by 1 and Reset Bit 0. A single set (1) bit is added to a message and then as many reset (0) bits as necessary are added to the same message. The total number of reset (0) bits added actually depends on the boundary of the message to which the message needs to be extended. In bit terms this is 1000... 0000, in hex byte terms this is 80 00... 0000.
For example, a message of 23 bit that is padded with 9 bits in order to fill a 32 bit block ... | 1011 1001 1101 0100 0010 0111 0000 0000|
Zero Padding : In zero padding, all bytes are padded with zero.
Example: In the following example the block size is 8 byte and padding is required for 4 byte ... |DD DD DD DD DD DD DD DD| DD DD DD DD 00 00 00 00 | Zero padding makes it impossible to distinguish between plain text data bytes and padding bytes as it is not reversible in the case when original file ends with one or more zero bytes
