What is the effective key size of DES?

The correct answer is A. 56 bits. DES uses a 64-bit key, but 8 of those bits are parity bits (one per byte) used for error checking, not actual encryption. This leaves only 56 bits of actual key material that contributes to the cipher's security. Therefore, the effective (cryptographic) key size of DES is 56…

Submitted by salim_om· Apr 18, 2026Cryptography

Question

Options

A56 bits
B64 bits
C128 bits
D1024 bits

How the community answered

(56 responses)

A
93% (52)
B
2% (1)
C
2% (1)
D
4% (2)

Explanation

DES uses a 64-bit key, but 8 of those bits are parity bits (one per byte) used for error checking, not actual encryption. This leaves only 56 bits of actual key material that contributes to the cipher's security. Therefore, the effective (cryptographic) key size of DES is 56 bits. This relatively small key size is why DES is considered insecure today - a 56-bit key space is vulnerable to brute-force attacks with modern hardware.

Topics

#DES#Key size#Symmetric encryption#Cryptography fundamentals

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