Triple DES (also known as 3DES or TDES), officially called the Triple Data Encryption Algorithm (TDEA), is a symmetric-key block cipher that applies the Data Encryption Standard (DES) algorithm three times to each data block. It was developed to address the vulnerabilities of single DES, which became susceptible to brute-force attacks as computational power increased.
How Triple DES Works
Encryption Process:
• Triple DES uses three 56-bit keys, typically referred to as K1, K2, and K3, forming a key bundle.
• The encryption process follows an Encrypt-Decrypt-Encrypt (EDE) sequence:
1. Encrypt with K1
2. Decrypt with K2
3. Encrypt with K3
• The process is applied to 64-bit blocks of data.
Decryption Process:
• The decryption reverses the steps:
1. Decrypt with K3
2. Encrypt with K2
3. Decrypt with K1
Key Variants:
• Three-key 3DES (3TDEA): Uses three independent keys (168 bits total, but effective security is 112 bits due to meet-in-the-middle attacks).
• Two-key 3DES: Uses K1 and K2, with K3 set equal to K1 (112 bits of keying, less secure than three-key but still stronger than single DES).
Security and Deprecation
• Triple DES significantly improved security over single DES, but it is slower and less secure than more modern algorithms like AES.
• Due to vulnerabilities such as meet-in-the-middle and block collision attacks (notably the Sweet32 attack exploiting its 64-bit block size), and its relatively limited effective key length, Triple DES has been deprecated by NIST as of 2019, with use disallowed (except for decrypting legacy data) after 2023.
• It remains backward compatible with DES, allowing for gradual transitions in legacy systems.