This homework requires you to use OpenSSL to decrypt some ciphertext.
OpenSSL is a popular open source library (and accompanying command line application) that implements many cryptographic operations and algorithms. It runs on Unix-like operating systems, including Linux and Mac OSX. You have several options to use it:
The version of OpenSSL that you use can be seen by running "openssl version". I am using: OpenSSL 1.0.1 14 Mar 2012.
I have a simple introduction to using OpenSSL. Read and try some operations. The basic way to decrypt is:
openssl enc -d -cipher-mode -in ciphertext.bin -out plaintext.txt -K keyinhex -iv ivinhex
To see the list of ciphers and modes try man encrypt. Note that options like -nopad are NOT needed.
Once you have OpenSSL installed and know the basics, your first task is to download your files at:
https://ict.siit.tu.ac.th/~uxxxxxxxxxx/private/
where xxxxxxxxxx is your student ID. You will be prompted for a username/password - it is the same as your Moodle login. The 4 files are: xxxxxxxxxx-ciphertext1.bin, xxxxxxxxxx-ciphertext2.bin, xxxxxxxxxx-ciphertext3.bin, xxxxxxxxxx-key.txt.
Now decrypt xxxxxxxxxx-ciphertext1.bin using OpenSSL and the key information in xxxxxxxxxx-key.txt. It was encrypted using DES with ECB mode of operation. Now view the plaintext.
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