How many bits is the effective length of the key of the Data Encryption Standard algorithm?

The correct answer is C. 56. The correct answer is "56". This is actually a bit of a trick question, since the actual key length is 64 bits. However, every eighth bit is ignored because it is used for parity. This makes the "effective length of the key" that the question actually asks for 56 bits. The other

Submitted by yuki_2020· Apr 18, 2026Cryptography

Question

Options

A168
B128
C56
D64

How the community answered

(46 responses)

A
2% (1)
B
2% (1)
C
91% (42)
D
4% (2)

Explanation

The correct answer is "56". This is actually a bit of a trick question, since the actual key length is 64 bits. However, every eighth bit is ignored because it is used for parity. This makes the "effective length of the key" that the question actually asks for 56 bits. The other answers are not correct because: 168 - This is the number of effective bits in Triple DES (56 times 3). 128 - Many encryption algorithms use 128 bit key, but not DES. Note that you may see 128 bit encryption referred to as "military strength encryption" because many military systems use key of 64 - This is the actual length of a DES encryption key, but not the "effective length" of the DES

Topics

#DES#Key length#Symmetric cryptography#Cryptographic algorithms

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