Overview: Block ciphers are the primary type of symmetric encryption algorithms in use today. They handle plaintext in fixed-size blocks, transforming them into ciphertext blocks of the same size. Key algorithms include the Data Encryption Standard (DES), Triple DES (3DES), and the Advanced Encryption Standard (AES).
Data Encryption Standard (DES):
- Introduced in 1977 as a federal standard, DES processes 64-bit plaintext blocks using a 56-bit key. It involves 16 rounds of processing with subkeys derived from the main key.
- Decryption mirrors encryption, using subkeys in reverse order.
- While DES has been heavily analyzed for weaknesses, its short key length (56 bits) makes it susceptible to brute force attacks. The 1998 success of the Electronic Frontier Foundation's crack demonstrated its vulnerability.
- Increasing hardware capabilities and decreasing costs mean that longer keys are necessary for security.
Triple DES (3DES):
- Standardized in the 1980s and incorporated into DES standards in 1999, 3DES uses three iterations of the DES algorithm with three keys, following an encrypt-decrypt-encrypt pattern. It supports key lengths of 112 to 168 bits.
- Its primary advantage is resisting brute-force attacks due to longer key lengths, but its complex nature makes it slow in software.
Advanced Encryption Standard (AES):
- AES was developed to replace 3DES, selected from a NIST contest that concluded in 2001 with the choice of the Rijndael algorithm.
- AES supports block sizes of 128 bits and key sizes of 128, 192, or 256 bits, emphasizing security, efficiency, and flexibility.
- It processes blocks through multiple rounds of substitution and permutation, significantly improving on DES and 3DES in terms of speed and complexity with larger block sizes and more efficient operation in software.
Overall, while DES laid the groundwork for block ciphers, its limitations in security drove the development of more robust algorithms like 3DES and AES, which are well-suited for modern cryptographic needs.
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