Computernetwerken 2 Lab 7: Symmetrical encryption K. Beheydt – G. Dierick – P. Geens For the first experiments, we will use Cryptool (http://www.cryptool.org) Rijndael / AES Gebruik CrypTool om een bruteforce analyse uit te voeren voor aes.hex. De gebruikte sleutel was 128 bits lang. Use CrypTool to bruteforce all possible keys on aes.hex. The key length is 128 bits. How long would it take to crack the key (according to CrypTool)? How long do you think it would take to crack the key if you knew the last 104 key bits are all zero? Try cracking the key using the knowledge that the last 104 key bits are 0. What was the encrypted message? How long did it take? Was your estimate of the time accurate? DiffieHellman As discussed in class, the DiffieHellman protocol allows exchanging a symmetric key over an insecure communication channel. Try it with your neighbour using 'Indiv. Procedures > DiffieHellman demo'. OpenSSL CrypTool is an educational tool, not meant for real world use. OpenSSL is a more serious tool (http://www.openssl.org). It's available on Debbie. Encrypting the file secret.txt using AES can be done like this: openssl enc aes128cbc in secret.txt out secret.txt.aes If you don't specify the in and out options, openssl will use the standard in and output stream. This means you can use it in pipes to encrypt or decrypt data. To decrypt the file created above and show the decrypted data on screen, use: openssl enc d aes128cbc in secret.txt.aes To get a list of all available encryption algorithms in OpenSSL, type: openssl listciphercommands Encrypt a file using Triple DES (des3). Send it to your neighbour for decryption. Use netcat and openssl to set up a secure communication channel with your neighbour. 1/1
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