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← 04ps-08 Oaep

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Showing Revision 1 created 10/24/2012 by Amara Bot.

  1. In this question, we'll introduce OAEP, which is Optimal Asymmetric Encryption Padding,
  2. OAEP is a padding scheme for use with RSA.
  3. It provides stronger assurances than the PKCS#1 scheme.
  4. In OAEP, we use two functions--
  5. G, which is a hash function outputting g bits,
  6. and H, which is another hash function outputting h bits.
  7. We also have r, a random nonce of g bits.
  8. We then take our message m and append to it 0's
  9. such that the length of m' is g.
  10. We then calculate x by concatenating two parts,
  11. First part is our message XORed with the output of the hash of r.
  12. The second part is r XORed with the hash of the first part.
  13. We then encrypt x using RSA and send off our message.
  14. For this assignment, you've been given a ciphertext, which was encrypted
  15. using OAEP and RSA, using the given encrypt function.
  16. Your task is to decrypt the ciphertext and put your answer into the plaintext variable.