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Security Fundamentals & Crypto · Foundational

Triple DES (3DES)

Symmetric cipher applying DES three times (encrypt-decrypt-encrypt) to increase effective key strength.

Definition

3DES (TDEA) uses two or three 56-bit keys, yielding a nominal 112 or 168-bit key but roughly 112 bits or less of effective security. It is slow and retains DES's 64-bit block size, making it vulnerable to Sweet32. NIST disallowed 3DES for encryption after 2023.

Example

Legacy payment HSMs still use 3DES keys for PIN blocks while migrating to AES.

Exam tip

3DES is deprecated; choose AES when asked to replace it.

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