# How does a block cipher work?

## How does a block cipher work?

Block Cipher

1. A block cipher encrypts data in blocks using a deterministic algorithm and a symmetric key.
2. As in the case of stream ciphers, most encryption methods encrypt bits one by one (stream ciphers).
3. A 128-bit block cipher brings 128 bits of plaintext and encrypts it into 128 bits of ciphertext.

## How do you achieve confidentiality with a block cipher?

In its most prevalent form, confidentiality is attained by encryption of bulk digital data using block ciphers. The block ciphers (e.g. DES 4]), which are used to encrypt fixed length data, are used in various chaining modes to encrypt bulk data. One such mode of operation is cipher block chaining (CBC) ( 1, 2, 3]).

What is the difference between a block cipher and a stream cipher?

The main difference between Block cipher and Stream cipher is that block cipher converts converts the plain text into cipher text by taking plain text’s block at a time. While stream cipher Converts the plain text into cipher text by taking 1 byte of plain text at a time.

### Does block cipher confidentiality?

The block cipher modes ECB, CBC, OFB, CFB, CTR, and XTS provide confidentiality, but they do not protect against accidental modification or malicious tampering. Modification or tampering can be detected with a separate message authentication code such as CBC-MAC, or a digital signature.

### What is the definition of a block cipher?

A block cipher is a method of encrypting text (to produce ciphertext) in which a cryptographic key and algorithm are applied to a block of data (for example, 64 contiguous bits) at once as a group rather than to one bit at a time.

How big of a block do you need for a block cipher?

A block cipher is one in which a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length. Typically, a block size of 64 or 128 bits is used.

#### Which is the encryption key for the ideal block cipher?

•The encryption key for the ideal block cipher is the codebook itself, meaning the table that shows the relationship between the input blocks and the output blocks. •Figure 1 depicts an ideal block cipher that uses blocks of size 4. Each block of 4 bits in the plaintext is transformed into a block of 4 ciphertext bits.

#### How is a cipher block produced in CBC?

In CBC, previous cipher block is given as input to next encryption algorithm after XOR with original plaintext block. In a nutshell here, a cipher block is produced by encrypting a XOR output of previous cipher block and present plaintext block. The process is illustrated here: