Identify Encryption Algorithm with 64-bit Blocks and Three 56-bit Keys

312-50v13 By islever Editorial Last updated

Cryptography

Short answer

B Triple Data Encryption Standard uses 64-bit data blocks and three 56-bit keys for enhanced security.

Question

In this form of encryption algorithm, every individual block contains 64-bit data, and three keys are used, where each key consists of 56 bits. Which is this encryption algorithm?
  1. IDEA
  2. Triple Data Encryption Standard Correct Answer
  3. AES
  4. MD5 encryption algorithm

Key Takeaways

The question tests knowledge of symmetric encryption algorithms by specifying block size and key structure, trapping candidates who confuse 3DES with modern standards like AES.

Triple Data Encryption Standard (3DES) uses 64-bit data blocks and three 56-bit keys, distinguishing it from AES and MD5. This page explains the specific parameters of 3DES to clarify common certification exam confusion.

Common mistake: Many learners select AES because it is the current industry standard, failing to notice that AES uses variable block sizes (128 bits) rather than the specified 64-bit blocks.

Expert Analysis

Why the Answer Is Correct

Triple DES (3DES or TDEA) is explicitly defined by its use of 64-bit data blocks and three independent 56-bit keys (derived from DES). The algorithm applies the DES cipher three times using these keys in an Encrypt-Decrypt-Encrypt sequence to enhance security while maintaining compatibility with legacy systems.

Why the Other Options Are Wrong

IDEA uses a 64-bit block size but employs 128-bit keys, not three 56-bit ones. AES supports 128-bit block sizes and key lengths of 128, 192, or 256 bits, making it incompatible with the question's constraints. MD5 is a hashing algorithm, not an encryption method, and does not use keys or blocks in this manner.

Community Comment Notes

Community consensus strongly favors option B, with users citing the specific characteristics of 3DES such as the EDE mode and key structure. Some dissenting votes for AES reflect a common misconception where candidates prioritize modern standards over the specific technical details provided in the prompt.

Exam Strategy

Focus on the specific numerical parameters (block size, key length, number of keys) provided in the question rather than guessing based on algorithm popularity. Memorize the distinct features of legacy algorithms like DES and 3DES alongside modern ones like AES.

Frequently Asked Questions

Why isn't AES the correct answer here?

AES uses 128-bit blocks and key sizes of 128/192/256 bits, whereas the question specifies 64-bit blocks and 56-bit keys.

How many keys does 3DES actually use?

It uses three 56-bit keys (K1, K2, K3), though often implemented as two keys (K1=K3) for backward compatibility.

More 312-50v13 FAQ →

Community Votes

B
80%
C
20%

80% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 4 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 4

  1. Osanyindoro 👍 2 Answered B
    Characteristics of Triple DES (3DES). -- It operates on 64-bit blocks of data. -- It uses three 56-bit keys (K1, K2, and K3), effectively providing a key length of up to 168 bits. -- The encryption process involves three operations: encrypting with K1, decrypting with K2, and encrypting again with K3 (Encrypt-Decrypt-Encrypt or EDE mode).
  2. 935f9c3 👍 1 Answered B
    B. Triple Data Encryption Standard
  3. srk970313 👍 1 Answered B
    B is the correct answer.
  4. lotusLettiva 👍 1 Answered C
    AES encryption

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