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3DES

As explained in Real-World Cryptography

3DES is a symmetric block cipher that applies the Data Encryption Standard transformation three times with multiple keys.

3DES is an older symmetric block cipher built from repeated DES transformations. Its 64-bit blocks helped legacy systems keep using DES while seeking stronger protection. section 13.2.2

Rather than encrypting card data, banking systems commonly use a per-card 3DES key to produce a MAC over a challenge. The bank computes or verifies that MAC to confirm the card’s identity. section 13.2.2

A bank card proves its identity

A smart card stores a unique 3DES secret. A reader or bank sends a challenge; the card generates a MAC, and the bank checks it using the customer’s corresponding key. Legacy hardware and software keep this arrangement in service, making periodic card replacement and key rotation important. section 13.2.2

How Real-World Cryptography covers it

How deep it goes
Defines 3DES as a 64-bit block cipher and explains its card-authentication role, without detailing its internal transformation steps.
Examples
Uses bank cards, per-card secrets, reader challenges, MACs, and periodic card replacement as concrete examples.
What you can do after
Evaluate how legacy smart-card systems use 3DES for authentication and why key rotation remains important.
How it connects
Connects symmetric cryptography, DES, message authentication codes, smart cards, secure elements, and key rotation.
Cover of Real-World Cryptography
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