3DES (Triple DES)
Triple DES (3DES) strengthens DES by encrypting each data block three times with 56-bit keys in an encrypt-decrypt-encrypt (EDE) sequence, yielding 168 bits of key material, and served as the transitional cipher between DES and AES.
Purpose
It provided a DES-backward-compatible security upgrade that resists brute-force attacks on DES before AES became widespread.
Mechanism
Ciphertext = E_K3(D_K2(E_K1(plaintext))). Setting K1=K3 gives 2-key 3DES with 112 effective bits; setting K1=K2=K3 degrades to single DES for backward compatibility. The block size stays 64 bits, and throughput is about one third of DES.
Use cases
- EMV chip cards in the financial industry
- Legacy PGP key encryption
- S/MIME compatibility profiles
- Legacy system migration
Examples
- Input
K1,K2,K3 + dataOutput8-byte ciphertextEDE mode
Common errors
- 2-key 3DES is vulnerable to Sweet32 birthday attacks
- Migrate to AES-256
Related terms
DES
The Data Encryption Standard (DES) is the symmetric block cipher standardized in 1977, using a 56-bit key and 64-bit blocks; it is obsolete due to its short key. GLOSSARY
AES
The Advanced Encryption Standard (AES) is the symmetric block cipher NIST standardized in 2001, supporting 128/192/256-bit keys, and is the de facto standard of modern encryption. GLOSSARY
Block Cipher
A block cipher is a symmetric cipher that encrypts and decrypts fixed-length blocks (e.g., 128 bits) and requires a mode of operation to handle arbitrary-length data. GLOSSARY