In cryptography, Triple DES (3DES or TDES), officially the Triple Data Encryption Algorithm (TDEA or Triple DEA), is a symmetric-key block cipher, which applies the DES cipher algorithm three times to each data block.

The 56-bit key of the Data Encryption Standard (DES) is no longer considered adequate in the face of modern cryptanalytic techniques and supercomputing power; Triple DES increases the effective security to 112 bits.

A CVE released in 2016, CVE-2016-2183, disclosed a major security vulnerability in the DES and 3DES encryption algorithms.

This CVE, combined with the inadequate key size of 3DES, led to NIST deprecating 3DES in 2019 and disallowing all uses (except processing already encrypted data) by the end of 2023.

While US government and industry standards abbreviate the algorithm's name as TDES (Triple DES) and TDEA (Triple Data Encryption Algorithm),[2] RFC 1851 referred to it as 3DES from the time it first promulgated the idea, and this namesake has since come into wide use by most vendors, users, and cryptographers.

[3][4][5][6] In 1978, a triple encryption method using DES with two 56-bit keys was proposed by Walter Tuchman; in 1981, Merkle and Hellman proposed a more secure triple-key version of 3DES with 112 bits of security.

[7] The Triple Data Encryption Algorithm is variously defined in several standards documents: The original DES cipher's key size of 56 bits was considered generally sufficient when it was designed, but the availability of increasing computational power made brute-force attacks feasible.

Triple DES provides a relatively simple method of increasing the key size of DES to protect against such attacks, without the need to design a completely new block cipher algorithm.

Unfortunately, this approach is vulnerable to the meet-in-the-middle attack: given a known plaintext pair

steps one would expect from an ideally secure algorithm with

It is still vulnerable to the meet-in-the-middle attack, but the attack requires 22 × 56 steps.This provides a shorter key length of 56*2 or 112 bits and a reasonable compromise between DES and keying option 1, with the same caveat as above.

[18] This is an improvement over "double DES" which only requires 256 steps to attack.

Generally, the three keys are generated by taking 24 bytes from a strong random generator, and only keying option 1 should be used (option 2 needs only 16 random bytes, but strong random generators are hard to assert and it is considered best practice to use only option 1).

However, ANS X9.52 specifies directly, and NIST SP 800-67 specifies via SP 800-38A,[19] that some modes shall only be used with certain constraints on them that do not necessarily apply to general specifications of those modes.

For example, ANS X9.52 specifies that for cipher block chaining, the initialization vector shall be different each time, whereas ISO/IEC 10116[20] does not.

FIPS PUB 46-3 and ISO/IEC 18033-3 define only the single-block algorithm, and do not place any restrictions on the modes of operation for multiple blocks.

However, this option is susceptible to certain chosen-plaintext or known-plaintext attacks,[21][22] and thus it is designated by NIST to have only 80 bits of security.

[16] This can be considered insecure; as a consequence, Triple DES's planned deprecation was announced by NIST in 2017.

blocks (785 GB) for a full attack, but researchers were lucky to get a collision just after around

The security of TDEA is affected by the number of blocks processed with one key bundle.

One key bundle shall not be used to apply cryptographic protection (e.g., encrypt) more than

64-bit data blocks.OpenSSL does not include 3DES by default since version 1.1.0 (August 2016) and considers it a "weak cipher".

[25] As of 2008, the electronic payment industry uses Triple DES and continues to develop and promulgate standards based upon it, such as EMV.

However, in December 2018, Microsoft announced the retirement of 3DES throughout their Office 365 service.

[30] Firefox and Mozilla Thunderbird use Triple DES in CBC mode to encrypt website authentication login credentials when using a master password.

[31] Below is a list of cryptography libraries that support Triple DES: Some implementations above may not include 3DES in the default build, in later or more recent versions.