Block and Stream Ciphers
Encryption algorithms can operate on blocks of data at a time, or bits and bytes of data, based on the type of cipher. Let’s compare the two methods.
Block Ciphers
A block cipher is a symmetric key (same key to encrypt and decrypt) cipher that operates on a group of bits called a block. A block cipher encryption algorithm may take a 64-bit block of plain text and generate a 64-bit block of cipher text. With this type of encryption, the same key to encrypt is also used to decrypt. Examples of symmetrical block cipher algorithms include the following:
Advanced Encryption Standard (AES)
Triple Digital Encryption Standard (3DES)
Blowfish
Digital Encryption Standard (DES)
International Data Encryption Algorithm (IDEA)
Block ciphers may add padding in cases where there is not enough data to encrypt to make a full block size. This might result is a very small amount of wasted overhead, because the small padding would be processed by the cipher along with the real data.
Stream Ciphers
A stream cipher is a symmetric key cipher (same key to encrypt as decrypt), where each bit of plaintext data to be encrypted is done 1 bit at a time against the bits of the key stream, also called a cipher digit stream. The resulting output is a ciphertext stream. Because a cipher stream does not have to fit in a given block size, there may be slightly less overhead than a block cipher that is requiring padding to complete a block size.
