TripleDES

TripleDES (also known as 3DES or TDES, officially the Triple Data Encryption Algorithm, TDEA) is a symmetric-key block cipher that enhances the security of the original Data Encryption Standard (DES) by applying the DES algorithm three times to each data block.

How TripleDES Works

TripleDES typically uses three separate 56-bit keys, labeled K1, K2, and K3, for a total key length of 168 bits, though some implementations use two keys with K1 reused as K3 (resulting in 112 bits of effective security). The most common mode is Encrypt-Decrypt-Encrypt (EDE):

1. Encrypt the plaintext with K1.
2. Decrypt the result with K2.
3. Encrypt the result again with K3.

To decrypt, the process is reversed: decrypt with K3, encrypt with K2, and decrypt with K1. Data is processed in 64-bit blocks.

Purpose and History

TripleDES was developed in the late 1990s as an interim solution to address the vulnerabilities of DES, which became susceptible to brute-force attacks as computing power increased. By applying DES three times, TripleDES significantly increased the key length and thus the difficulty of breaking the encryption.

Security and Limitations

TripleDES can use a 168-bit key, due to known cryptanalytic attacks (such as meet-in-the-middle), its effective security is considered to be 112 bits.

In 2016, a major vulnerability (CVE-2016-2183) was disclosed, affecting both DES and TripleDES. This, combined with the small block size (64 bits), makes it vulnerable to certain attacks, especially when encrypting large amounts of data with the same key. As a result of these vulnerabilities and the emergence of more robust algorithms like AES, TripleDES has been deprecated by NIST since 2019 and is disallowed for most uses (except processing already encrypted data) after 2023.