CREST Practitioner Security Analyst (CPSA) Practice

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What is the key size of 3DES encryption?

56 bits
168 bits
256 bits
128 bits

The correct answer is: 168 bits

Three-Fish (3DES), or Triple DES, is a symmetric key block cipher that applies the older Data Encryption Standard (DES) algorithm three times to each data block. The key size for 3DES is 168 bits, which results from utilizing three separate DES keys, each of 56 bits. In 3DES encryption, each of the three keys is used in a sequence of encrypting and decrypting operations. While the theoretical maximum key size can include one of the keys being repeated (which would effectively make it use only 112 bits in certain configurations), the full implementation using three unique keys indeed totals to 168 bits. This enhanced key length significantly strengthens the encryption against brute-force attacks compared to the original DES, which had only a 56-bit key. This is why the key size of 3DES encryption is correctly identified as 168 bits.