OCR MEI C4 2010 January — Question 8

Exam BoardOCR MEI
ModuleC4 (Core Mathematics 4)
Year2010
SessionJanuary
TopicNumber Theory

8 A passage of plaintext is encoded by using the Caesar cipher corresponding to a shift of 2 places followed by the Vigenere cipher with keyword ODE.
  1. The first letter in the plaintext passage is \(F\). Show that the first letter in the transmitted text is \(V\).
  2. The first four letters in the transmitted text are VFIU. What are the first four letters in the plaintext passage?
  3. The 800th letter in the transmitted text is \(W\). What is the 800th letter in the plaintext passage?