SUNY Geneseo Department of Computer Science

Cryptography

Previous Lecture

Misc

Lab available in lab sessions tomorrow

End-of-Semester

• CS Dept. holiday party
  • Wed. Dec. 10, 3:00 PM
  • Place TBA
  • Sign up in Dept. office
• SOFIs in class next Monday (12/8)
  • Need a czar/czaritza
• Final
  • Monday, Dec. 15, 8:00 AM
  • Comprehensive but biased towards material since exam 2
  • Same format and rules as hour exams
  • Designed for 2 hours, 3 available
  • Donuts & cider
  • Sample questions will be on the Web

Questions?

Skylines for lab, generating negative as well as positive displacements?

    Random r = new Random();

• r.nextGaussian() will return a random real number most probably between -1.0 and +1.0

Counting movePen's in a loop?

    star( n )
        for i = 1 to 5
            movePen
            recursion

• M(n) = # of movePen's
• M(n) = 5 + 5M(n-1) if n > 1

Factoring & Cryptography

Section 16.3.2

Sending messages between sender & receiver securely = cryptography

Symmetric key = sender & receiver share a key

Public key = receiver has public key & a private key

• Different, private key not computable from public one
• Sender encrypts w/ receiver's public key
• Receiver decrypts w/ receiver's private key

Summary of RSA (details may be wrong)

• n = p * q
• e = encryption, public
• d = decryption, private
• e, d depend on p & q
• Public key = (e, n)
• Private = (d,n)
• Encoded m = m^e mod n (?) = x
• Decode by x^d mod n (?)

Next

I will look up the details of RSA so we can work through a concrete example.

Next Lecture