2024/2025: Segurança da Informação (Information Security) - 1º MCI

8.Oct.2024

Practical work 3

Introduction to ciphering*

  1. Google a bit for ciphering (or encryption) tools (and related conceptual information, if you want).
  2. From your findings:
  3. Create a setup folder on your machine, with some text files for ciphering experimentation.
  4. Run the ciphering software, trying different algorithms (AES, RSA...), with some plaintext content, and save the corresponding ciphertext. (Take care of the different formats, or representations, of data: Raw, Hex, Base64, ...)
  5. Analyze the difference of data (plaintext and ciphertext) and the difference of parameters needed for the operation of the different algorithms.
  6. Try to see what happens with ciphertext when the plaintext has blocks with same content (with ECB and with CBC).
  7. Encipher some text and send the corresponding ciphertext to a colleague, by email. What information has to be known to your colleague, for her/him to be able to decipher the ciphertext? What items of that information are really sensitive?
  8. Take some conclusions on the operational difference (keys, parameters...) of the different algorithms.

* cyphering, in British

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(To be made after class and by oneself!)

(To be made after class and by oneself!)

(To be made after class and by oneself!)

Assessment 3

Assessment of Practical classes - ciphering

Using the (on-line) cryptographic tools that you have played with in your practical class on Introduction to ciphering, answer the following questions and send them in a short report, for evaluation.

  1. Recover the original plaintext of the following ciphertexts (in hexadecimal)*, produced with the cryptographic algorithms and operational parameters shown:

    (*) Note: quotes are not part of the data, just delimit it.
    Please, identify the cryptographic tool you used.

  2. Recover the original plaintext of the ciphertexts in the named files (in binary, or "raw", format), produced with the cryptographic algorithm RSA with the public keys that match the private keys shown:

    Please, identify the cryptographic tool you used.

  3. Do you have some comments, about what you have done and noticed?

* The "numeric" format of RSA keys as shown in cryptography class (e,n) or (exponent, modulus), can be seen with specific tools.
For instance, with openSSL: openssl rsa -in RSAkey.pem -text -noout .