Question

Question # 5.

a. Pretty Good Privacy (PGP) is broadly used to secure email communication. Explain the steps needed prior to exchanging email messages with privacy and authenticity guarantees for a pair of users using PGP.

b. Estimate the time required to crack a 56-bit DES key by a brute-force attack using a 3000 MIPS (million instructions per second) computer, assuming that the inner loop for a brute-force attack program involves around 15 instructions per key value, plus the time to encrypt an 8-byte plaintext. Perform the same calculation fora 128-bit IDEA key.

Extrapolate your calculations to obtain the cracking time fora 300,000 MIPS parallel processor (or an Internet consortium with similar processing power).

Answer 1

A.When a user encrypts plaintext with PGP, PGP first compresses the plaintext. Data compression saves modem transmission time and disk space and, more importantly, strengthens cryptographic security. Most cryptanalysis techniques exploit patterns found in the plaintext to crack the cipher. Compression reduces these patterns in the plaintext, thereby greatly enhancing resistance to cryptanalysis.

PGP then creates a session key, which is a one-time-only secret key. This key is a random number generated from the random movements of your mouse and the keystrokes you type. This session key works with a very secure, fast conventional encryption algorithm to encrypt the plaintext; the result is ciphertext. Once the data is encrypted, the session key is then encrypted to the recipient's public key. This public key-encrypted session key is transmitted along with the ciphertext to the recipient.

B. More information is required. Please put full question. Thankyou