Triple DES (3DES) or the Triple Data Encryption Algorithm (TDEA) is a refinement of the original Data Encryption Standard (DES).

Triple DES is described in NIST Special Publication 800-67. The original specification is in ANSI X9.52.

Vulnerabilities In 3DES Encryption Put It Out To Pasture In IBM i November 14, 2016 Alex Woodie IBM i customers should stop using 3DES, also known as Triple DES, ciphers due to the SWEET32 vulnerabilities that could leave sensitive information unprotected as it moves between client and server via the OpenSSL and OpenVPN protocols.

TDEA involves using three 64-bit DEA keys (K1, K2, K3) in Encrypt-Decrypt-Encrypt (EDE) mode, that is, the plain text is encrypted with K1,then decrypted with K2, and then encrypted again with K3.You will sometimes see this referred to as des-ede mode.

A TDEA key thus consists of three keys (K1, K2, K3). The three keys are also referred to as a key bundle. The key bundle is 3 x 64 = 192 bits long.

ANSI X9.52 describes three options for the selection of keys in a bundle.Option 1, the preferred option, employs three mutually independent keys (K1 K2 K3 K1).Option 2 employs two mutuallyindependent keys and a third key that is the same as the first key (K1 K2 and K3 = K1). Option 3 is a key bundle of three identical keys (K1 = K2 = K3). Option 1 gives a keyspace of 3 x 56 = 168 bits.

I have a triple DES key. What are its sub-keys?

Just split the 192-bit triple DES key into 3 separate 64-bit keys, working from left to right.For example, if your triple-DES key is the 192-bit value (in hex format):

then split it into the three sub-keys, K1, K2 and K3, each of 64 bits:

So the sub-keys are K1=0x0123456789ABCDEF, K2=0xFEDCBA9876543210 and K3=0x89ABCDEF01234567.

Can I do single-key DES encryption with a Triple DES function?

If you encrypt something, then decrypt it and encrypt it again with the same key, you've just done the same as encrypting it once. Thusoption 3 with three identical keys is simply the original 64-bit DEA algorithm with a keyspace of 56 bits, albeit done with three times as much effort.So, to carry out 'single' DES using a Triple DESfunction, just set all three DEA keys to be the same. Note that this option is no longer permitted under NIST SP 800-67.

For example, if your single-DES key is 0x89ABCDEF01234567 then set your Triple-DES key to be

What's two-key triple DES encryption?

Two-key triple DES is option 2 where we encrypt with K1, then decrypt with K2 and finally encrypt again with K1. The keyspace is thus 2 x 56 = 112 bits.

For example, with K1=0x0123456789ABCDEF and K2=0xFEDCBA9876543210you would set the triple DES key to be0x0123456789ABCDEFFEDCBA98765432100123456789ABCDEF.

How long is a triple DES key: 192 or 168 bits?

As mentioned above, a triple DES key is a bundle of three DES keys.A DES key is 64 bits long, but only 56 bits of these are used in the encryption process.

A triple DES key is therefore 3 x 64 = 192 bits long, but the keyspace is only 3 x 56 = 168 bits.

Note that if your 'triple DES' key is not exactly 192-bits long - i.e. exactly 24 bytes long, or 48 hexadecimal digits -then you do not have a valid triple DES key.

The other 8 bits are meant to be used as error detecting or 'parity' bits so, in principle, the validity of the key bit string can be checked (every byte should be of odd parity), but this is hardly ever done.Most people and most software packages, including CryptoSys API and CryptoSys PKI, do not bother to check the parity of the key and just ignore the state of the parity bits.Be careful, though, because this means that the keys represented, for example, by the following bit strings are treated as being equal,and will produce identical ciphertext output for the same plaintext input:

Modes of operation

X9.52 describes seven different modes for using TDEA.CryptoSys API and the CryptoSys PKI Toolkitsupport the five most useful of these: Electronic Codebook (ECB), Cipher Block Chaining (CBC),64-bit Cipher Feedback mode (CFB), Output Feedback mode (OFB) and Counter mode (CTR).

Other references

• NIST Special Publication 800-20Modes of Operation Validation System for the Triple Data Encryption Algorithm (TMOVS): Requirements and Procedures, April 2000
• NIST Special Publication 800-38ARecommendations for Block Cipher Modes of Operation, Methods and Techniques, Morris Dworkin, December 2001.

Triple DES functions available in CryptoSys API

Recommended functions and methods

We recommend you use the CIPHER functions and Cipher methods with the tdea option.

Original Triple DES-specific functions (deprecated)

• TDEA_Hex - en/decrypt a hex string in one step using ECB mode
• TDEA_HexMode - en/decrypt a hex string in one step using specified mode (EBC, CBC, CFP, OFB, CTR)
• TDEA_Bytes - en/decrypt a byte array in one step using ECB mode
• TDEA_BytesMode - en/decrypt a byte array in one step using specified mode (EBC, CBC, CFP, OFB, CTR)
• TDEA_File - en/decrypt a file in one step
• TDEA_FileHex - en/decrypt a file in one step using a key in hex format
• TDEA_Init - initialise the context ready for repeated use
• TDEA_InitHex - initialise the context using hex values ready for repeated use
• TDEA_Update - en/decrypt the next set of data and update the context
• TDEA_UpdateHex - en/decrypt the next set of data in hex and update the context
• TDEA_Final - close and clear the context

The equivalent .NET methods are in the Tdea Class.

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This page last updated 11 January 2019

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According to draft guidance published by NIST on July 19, 2018, the Triple Data Encryption Algorithm (TDEA or 3DES) is officially being retired. The guidelines propose that, after a period of public consultation, 3DES is deprecated for all new applications and usage is disallowed after 2023.

Background on the 3DES Guidance

First introduced in 1998, the 3DES algorithm is still broadly adopted in finance, payment and other private industry to encrypt data in-transit and at-rest, including EMV keys for protecting credit card transactions. The proposal to formally retire the algorithm is not entirely surprising, especially considering historical movements by NIST:

• The Advanced Encryption Standard (AES) was introduced in 2001 to replace 3DES
• Data Encryption Standard (DES), the algorithm 3DES is based on, was retired in 2005
• The two-key variant of 3DES was retired in 2015

In July 2017, NIST initially proposed retiring 3DES following a security analysis and practical demonstration of attacks on 3DES in several real-world protocols. In November 2017, NIST restricted usage to 220 64-bit blocks (8 MB of data) using a single key bundle, so it could no longer effectively be used for TLS, IPsec, or large file encryption.

NIST Terminology

• Deprecated means “the use of the algorithm and key length is allowed, but the user must accept some risk.”

• Disallowed means an “algorithm or key length is no longer allowed for the indicated use.”

The designation of a major encryption algorithm as a security risk has implications to US Federal Institutions and vendors subject to NIST guidelines. This announcement is also a reflection on best practices for institutions in the finance industry, and could impact PCI cryptography recommendations.

What is 3DES?

The Triple Data Encryption Algorithm, alternately referred to as Triple DES (Data Encryption Standard), 3DES, TDES, Triple DEA, or TDEA, is a symmetric key-block cipher which applies the DES cipher in triplicate by encrypting with the first key (k1), decrypting with the second key (k2), and encrypting with the third key (k3). A two-key variant also exists, where k1 and k3 are the same.

Why 3DES is Likely to Be Disallowed after 2023

3DES is a ciphersuite based on the Data Encryption Standard developed by IBM in the early 1970s and adopted by NIST (with minor changes) in 1977. 3DES was introduced during a period of transition between two major algorithms. In 1997, NIST announced a formal search for candidate algorithms to replace DES. In 2001, AES was released with the intention of coexisting with 3DES until 2030, permitting a gradual transition. However, the retirement of 3DES has been likely accelerated by research which has revealed significant vulnerabilities and is, by some accounts, long overdue.

NIST first initiated discussion of deprecating 3DES following the analysis and demonstration of attacks on 3DES. The Sweet32 vulnerability was made public by researchers Karthikeyan Bhargavan and Gaëtan Leurent. This research exploited a known vulnerability to collision attacks in 3DES and other 64-bit block cipher suites which are greatest during lengthy transmissions, the exchange of content files, or transmissions vulnerable to text injection. After the exposure of this vulnerability, NIST proposed 3DES be deprecated, and soon thereafter, restricted its usage.

Understanding the Implications of 3DES’ Deprecation

3DES is a major algorithm, and one which is deeply embedded into payment systems, standards and technology in the finance industry. The five-year timeline proposed by NIST to disallow the use of 3DES could present challenges for the industry due to non-upgradable infrastructure, billions of credit cards in circulation and potential interoperability issues.

Organizations using 3DES should be aware of how this algorithm is used within their network environment and the cloud, including its use by vendors. Working to develop an understanding of 3DES implementations can enable organizations to proactively manage 3DES risks with regards to discovered vulnerabilities within the algorithm and the sensitivity of business data.

To protect mission-critical data during the transition period to AES or another method of encryption, organizations can adopt stop-gap measures, such as changing 3DES keys more frequently.

Achieving Crypto-Agility

Organizations should be aware of the dangers created by inertia or accepting the business risks of deeply-embedded ciphersuites which are insecure. With the threat of quantum computing on the horizon, threatening to break many of today’s most popular algorithms, NIST’s recommendation is for organizations to “plan for cryptographic agility to facilitate transitions to quantum-resistant algorithms where needed in the future.“

As firms consider compliance and threats, crypto-agility can enable fast response to emerging research and recommendations by supporting the transition from one encryption standard to another at a moment’s notice. Solutions for cryptography as a service enable organizations in highly-regulated industries to protect business-critical data with globally compliant solutions for encryption.

References

• Draft NIST Special Publication 800-131A Revision 2: Transitioning the Use of Cryptographic lgorithms and Key Lengths(July 2018) by the National Institute of Standards and Technology
• Federal Information Processing Standards Publication 197: Announcing the Advanced Encryption Standard (AES) (1997), by the National Institution of Standards and Technology
• Federal Information Processing Standards Publication 46-3: Data Encryption Standard (DES) (1999), by the National Institute of Standards and Technology
• News: Update to Current Use and Deprecation of TDEA (July 2017), by the National Institute of Standards and Technology
• NIST Special Publication 800-67, Revision 2: Recommendations for the Triple Data Encryption Algorithm Block Cipher (November 2017), by the National Institute of Standards and Technology
• News: Announcing Development of Federal Information Processing Standard for Advanced Encryption (January 1997), by the National Institute Of Standards and Technology
• Cryptomathic Answers Compliance-Driven Call for Crypto-Agility (May 2018), by Cryptomathic

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