What is the difference Between Block Cipher and Stream Cipher?

The difference between block ciphers and stream ciphers lies in how they process and encrypt data. Here is a detailed comparison:

Block Cipher

Definition

A block cipher is a symmetric-key encryption method that processes fixed-length groups of bits, called blocks, into encrypted ciphertext blocks of the same length[4][7].

Operation

• Process: Encrypts data in fixed-size blocks (e.g., 64 bits, 128 bits, or 256 bits)[4][7].
• Encryption: Each block of plaintext is encrypted independently using a key and a cryptographic algorithm[4][7].
• Decryption: The decryption algorithm is the inverse of the encryption algorithm, allowing the original plaintext to be recovered from the ciphertext[4][7].

Characteristics

• Speed: Generally slower than stream ciphers due to the processing of large blocks of data[1][2][3].
• Security: Typically more secure than stream ciphers, especially when using strong encryption modes and key management practices[2][3][4].
• Modes of Operation: Includes ECB (Electronic Code Book), CBC (Cipher Block Chaining), CFB (Cipher Feedback), OFB (Output Feedback), and CTR (Counter)[1][2][10].
• Examples: AES (Advanced Encryption Standard), DES (Data Encryption Standard), Blowfish[4][7][18].

Use Cases

• Suitable for applications that handle large amounts of data, such as file transmission, email, and database encryption[2][3][4].

Stream Cipher

Definition

A stream cipher is a symmetric-key encryption method that encrypts data one bit or byte at a time, using a pseudorandom keystream generated from a key[5][6][8].

Operation

• Process: Encrypts data bit-by-bit or byte-by-byte[1][2][5].
• Encryption: Each bit or byte of plaintext is encrypted individually by XORing it with a bit or byte from the keystream[1][5][6].
• Decryption: The ciphertext is decrypted by XORing it with the same keystream used for encryption[5][6][8].

Characteristics

• Speed: Generally faster than block ciphers due to the bit-by-bit or byte-by-byte processing[1][2][3].
• Security: Can be less secure than block ciphers if the keystream is not properly managed or if the same keystream is reused[2][3][5].
• Types: Includes synchronous stream ciphers (keystream generated independently of plaintext/ciphertext) and self-synchronizing stream ciphers (keystream depends on previous ciphertext bits)[5][8][14].
• Examples: RC4, Salsa20, ChaCha20[6][8][14].

Use Cases

• Suitable for applications requiring real-time encryption, such as video streaming, online gaming, and secure internet communications[2][3][6].

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