Table 1. First O chosen bits in key 8 bit 16 bit 24 bit 32 bit Effective key length 48 bits 40 bits 32 bits 24 bits Bruteforce time 7244 days 20hours 19minutes 20 days 19 hours 4minutes 4hours 46 minutes 17 seconds Task 1 (1%): Encrypt an example text with Cryptool. For the key lengths of 56 bits, enter the input key of 64 bits to obtain the encrypted output. Each time, the leftmost bytes will be chosen as 0 as shown in Table 1. Then run the bruteforce analysis in Cryptool and report the shown time for cracking the key. Show the screenshots in your report. Table 1. Bruteforce time First O chosen bits in key 8 bit 16 bit 24 bit 32 bit Effective key length 48 bits 40 bits 32 bits 24 bits Task 2 (1%): a) For the effective key length of 32 bits (first 24 bits of input key entered as 0, and assumed to be known to the attacker) run the full bruteforce DES analysis in Cryptool and report all the found plaintexts and choose the one with correct language and report the decrypted text. Show the screenshots in your report. b) Repeat the same task with an effective key length of 24 bits. Compare the results of this experiment with what you got in part (a).

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EXPERT ANSWER

Ans(a)

There are several ways of classifying cryptographic algorithms. For purposes of this paper, they will be categorized based on the number of keys that are employed for encryption and decryption, and further defined by their application and use. The three types of algorithms that will be discussed are:

Secret Key Cryptography (SKC): Uses a single key for both encryption and decryption; also called symmetric encryption. Primarily used for privacy and confidentiality.

Public Key Cryptography (PKC): Uses one key for encryption and another for decryption; also called asymmetric encryption. Primarily used for authentication, non-repudiation, and key exchange.

Hash Functions: Uses a mathematical transformation to irreversibly “encrypt” information, providing a digital fingerprint. Primarily used for message integrity.

Ans(b)

Data encryption standard (DES) has been found vulnerable against very powerful attacks and therefore, the popularity of DES has been found slightly on decline.

DES is a block cipher, and encrypts data in blocks of size of 64 bit each, means 64 bits of plain text goes as the input to DES, which produces 64 bits of cipher text. The same algorithm and key are used for encryption and decryption, with minor differences. The key length is 56 bits. The basic idea is show in figure.