Encryption Decryption

1
Encryption / Decryption

• Ryan Bolt Quincy Styke
• ECE 551
• Fall 2006
• rbolt_at_utk.edu, qstyke_at_utk.edu

2
Outline

• Introduction (Background)
• System Requirements
• Specifications
• Summary of Flow
• Input / Output Diagram
• VHDL Modules

3
Background of Vigenere

• The Vigenere algorithm is a poly-alphabetic
  cipher based on a 2-dimensional alphabet array
  (26x26)
• The benefit of the poly-alphabetic cipher is that
  it is impervious to letter-frequency analysis
  (i.e. the letter e is most popular in the
  English language)
• Instead of one-to-one relationships between
  plaintext and cipher-text, there exists a
  many-to-one relationship using poly-alphabetic
  ciphers.
• Vigenere uses a repeating keyword to encrypt the
  plaintext with the 26x26 array. Below is an
  example using the key relations
• Keyword RELAT IONSR ELATI ONSRE LATIO
  NSREL
• Plaintext TOBEO RNOTT OBETH ATIST HEQUE
  STION
• Ciphertext KSMEH ZBBLK SMEMP OGAJX SEJCS FLZSY
  

4
System Requirements

• Encrypt Decrypt modules
• Using Vigenere algorithm
• Input Output Modules
• Pushbutton/Switch Input Support
• Input plaintext and ciphers using a scrolling
  alphabet
• Possible additional feature read input from
  keyboard
• Ability to input key and plaintext or cipher-text
  as strings
• Seven Segment Output Support
• Output encrypted cipher or decrypted plain text
• Possible additional feature output ASCII
  ciphers/strings to CRT
• Ability to output cipher-text or plaintext
  strings
• Self Test
• Showcase the basic encrypt / decrypt functions
  using a known plaintext cipher-text

5
Specifications

• Key Inputs
• Key character array
• Plaintext character array
• Ciphertext character array (decrypt mode)
• Key Outputs
• Ciphertext character array
• Plaintext character array (decrypt mode)

6
Project Flow

• Power On
• Input Key via pushbuttons, press btn3 to confirm
• Slide switch determines encrypt (1) or decrypt
  (0)
• Input Plaintext or Cipher-text via pushbuttons,
  press btn3 to confirm
• Cipher-text or Plaintext output will scroll
  through the seven segment displays
• Press btn3 to enter new plaintext or cipher-text

7
Input/Output Diagram
8
VHDL Modules
FPGA
Input Handler (PB, switches, (KB))
Encryption
Control Module
Output Function (7seg, (CRT))
Decryption
Self Test