DES Encryption Process - DES with Cryp Tool - Engineering Assignment Help

Assignment Task :

1. Aims

The aims of this practical work are 

• To reinforce understanding of the DES symmetric key cipher. 

• To reinforce understanding of the AES symmetric key cipher.

• To illustrate the differences between the DES and AES encryption algorithms.

• To highlight the vulnerability of the ECB and CBC modes of operation of a symmetric block cipher to attack.

• To reinforce understanding of the Diffie-Hellman key exchange algorithm. 

• To reinforce understanding of the behaviour and use of hash functions.

• To reinforce understanding of the RSA public key cipher. 

• To reinforce understanding of public key infrastructure

• To reinforce understanding of hybrid ciphers.

2. Learning Outcomes

After completing this practical work you will

• Be aware of the main differences between DES and AES. 

• Understand the advantages of the CBC mode of operation over the ECB mode of operation of a symmetric key block cipher.

• Understand the vulnerability of the ECB mode of operation and the CBC modes of operation of a symmetric key block cipher to cut and paste attacks.

• Understand the significance of the key length of a modern cipher.

• Understand the Diffie-Hellman key exchange algorithm and its vulnerability to attack.

• Understand how to do a byte addition attack on a hash function and its significance in practice.

• Understand how the RSA key cryptosystem operates upon its input by treating it as an integer value. Understand the significance of the size of the value of the modulus used in RSA. 

• Know what the typical content of a Digital Certificate looks like.

• Have an appreciation of the time RSA operations take.

• Have worked through the steps taken in encrypting and decrypting a document using a hybrid cipher.

Q1. Provide screenshots of the message and the ciphertext. Provide a screenshot of the window showing the decrypted ciphertext. Give the key you used.

Encrypt the same plaintext message using the same process and the same key as above only selecting Crypt/Decrypt > Symmetric (modern) > DES (CBC) instead.   

Q2. Provide a screenshot of the resulting ciphertext. Compare the ciphertext with that obtained using DES (ECB), and report what you notice

Q3. Provide a screenshot of the ciphertext and report what you notice about it. 

Close the window showing the ciphertext of Q3. and then encrypt the plaintext file with the CBC variant of the DES cipher.

Q4. Provide a screenshot of the ciphertext obtained using the CBC variant of DES, compare it with that of Q3. and report what you notice. What do you think the significance of what you notice is? 

Select Indiv. Procedures > Visualization of Algorithms > DES and watch through the whole of the demonstration of DES provided. This should help to reinforce your understanding of this cipher.

Q5. What impression do you get of the nature of the DES encryption process from the demonstration? 

1. AES demonstration

Select Indiv. Procedures > Visualization of Algorithms > AES > Rijndael Animation and watch through the whole of the demonstration of AES provided. This should help to reinforce your understanding of this cipher.

Q6. What main differences do you notice between the AES encryption process and the DES encryption process from the demonstration? 

Q7. Compare the total size of the S boxes of DES with that of the S box of AES. 

2. Analysis of modern symmetric key ciphers

Q8. Encrypt a plaintext message of at least 64 characters with DES (ECB), DES (CBC), and AES. For each ciphertext use the corresponding analysis tool provided in Cryptool to attempt to decrypt the ciphertext. In each case give the time it will take to do the decryption (provided by the analysis tool). Compare the three values and explain their relative magnitudes.   

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