Symmetric Ciphers Modes | My Assignment Tutor

Lab- Symmetric Ciphers Modes   Objective:     To test different modes in symmetric ciphers    Background / Scenario Symmetric key cryptography provides several modes of operation, including Electronic Codebook (ECB), Cipher-Block Chaining (CBC), Cipher Feedback (CFB), Output Feedback (OFB), and Counter Mode (CTR. Modes of operation have been devised to encipher text of any size employing either DES or AES. Two important properties of these encryption modes that this lab will explore are pattern preservation and error propagation. Pattern preservation means that a block of plaintext is encrypted into a block of cipher text the same way every time; e.g. if Salem finds out that cipher text blocks 1, 5, and 10 are the same, he knows that plaintext blocks 1, 5, and 10 are the same. Error propagation means that a single bit error in transmission of a cipher text block creates errors in not only the decryption of the affected block, but propagates to the following blocks of the message.  Required Resources Cryptool 1.0   Step 1: Install cryptool Open a web browser and navigate to http://www.cryptool.org/en . b. Click Download in the CrypTool1 c. Open the Setup Cryptool.exe e. complete the installation steps . Click Finish on the last screen, Cryptool  is now installed and running. Step 2 Implement DES cipher. Open a new file and type a plaintext message Click from the menu Encrypt/Decrypt > Symmetric (modern) > DES (ECB)… This presents a key selection window, this key must be 64 bits long, which equates to 8 hexadecimal figures. For simplicity use the default key of: 00 00 00 00 00 00 00 00 Select Encrypt and there should be presented a window showing the data encrypted in hexadecimal form and its corresponding ASCII representation. To decrypt the message again select Crypt/Decrypt > Symmetric (modern) > DES (ECB)… Use the same key and select Decrypt, and the original message will be displayed in hexadecimal representation Encrypt the same message using the same process as above only selecting Crypt/Decrypt > Symmetric (modern) > DES (CBC)… instead. Comparing the two encrypted messages, you should notice they start with the same 8 bytes, but then they are not the same Step 3 Implement AES cipher. Open a new file and type a plaintext message Click from the menu Crypt/Decrypt > Symmetric (modern) > AES (CBC)… This presents a key selection window, this key could be 128 or 192 or 256 bits long. Use the key length 128 bits, which equates to 16 hexadecimal figures. For simplicity use the default key of:                            11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 Select Encrypt and there should be presented a window showing the data encrypted in hexadecimal form and its corresponding ASCII representation. To decrypt the message again select Crypt/Decrypt > Symmetric (modern) > AES (CBC). Use the same key and select Decrypt, and the original message will be displayed in hexadecimal representation Step 4:  Investigate Properties of Modes in DES and AES You should test pattern preservation by encrypting plaintext that includes a pattern, and examining the cipher text to see if the pattern is preserved. You should test error propagation by modifying one byte of the cipher text prior to decryption, and then examining the decrypted plaintext. Fill in each block with a yes, no, or other comment.    DESECBCBCPattern preservation  Error propagation      AESCBCPattern preservation Error propagation  Hint: To test pattern preservation property, you can include repeated blocks in your plaintext and observe the results of cipher text.To test error propagation property, you can encrypt plaintext first and then modify one bit in ciphertext and check the decryption results. Step 5:  Scenarios Based on your findings in Step 5. Which mode (ECB or CBC) would be most appropriate for each of the following scenarios, and give a brief justification   An online bank statementAn encrypted VoIP sessionViewing of a website using TCP/IP

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