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Lab 8 - Cryptography
- [3p] Steganography
- Several tools can be used to hide files behind an image. Create a file
Lab08.txtand add the following line: “Thank GOD that this lab is NOT part of the exam.”- Use
outguessto hideLab08.txtbehind a jpg file of your choice. Retrieve the contents from the jpg file. - You can install
outguesswithapt-get install outguess. - Add
fileype:jpgto your Google search to only show jpg results.
- Sometimes concatenating files is enough to hide them. Use
zipandcatto hideLab08.txtbehind a JPG file of your choice. Useunzipto retrieve the file.unzipskips over junk found at the beginning of the file.
- Which of the two methods uses less space? Why is that?
- [+1p=4p] Write in a notepad your name using the Caesar cipher. The key is equal to the number of letter in your name. (use both first and last names)
- [+1p=5p] Use frequency analysis to decrypt this file. You can use any tool you want.
- The plaintext is in English and the Vigenere algorithm was used for encryption.
- More information about the Vigenere cipher can be found here: Vigenère_cipher.
- [+2p=7p] You have to use the following algorithm1) to decrypt the message “08324F5C”.
const char *xlat = "dsfd;kfoA,.iyewrkldJKDHSUBsgvca69834ncxv"; char *unseven(const char *hash) { unsigned int key, i, hlen = strlen(hash) - 2; char *plain = (char*)malloc(hlen / 2 + 1); if (hlen < 2 || hlen & 1) return NULL; key = (hash[0] - '0') * 10 + hash[1] - '0'; if (key > 15 || !isdigit(hash[0]) || !isdigit(hash[1])) return NULL; hash += 2; for (i = 0; i < hlen; ++i) if (!isxdigit(hash[i])) return NULL; for (i = 0; i < hlen; i += 2) { plain[i / 2] = ((hex2int(hash[i]) << 4) | hex2int(hash[i + 1])) ^ xlat[key++]; if (key == 40) key = 0; } plain[hlen / 2] = 0; return plain; }
- [+2p=9p] TODO
- [+2=11p] Encryption contest. Create a symmetric encryption algorithm that uses substitution/transposition method applied directly on a block. Start!
1)
Interesting fact: this algorithm is used for type 7 decryption in Cisco IOS.
