This is the Third in a series of "Intro to Cryptanalysis" Challenges to teach some mad skills in ciphers and decrypting for those that have little to no experience with them. If you haven't already look at Intro to Cryptanalysis - Concealment or Transposition I suggest starting there.

1. Concealment Cipher

2. Transposition Cipher

3. Substitution Cipher

Substitution Cipher - Substitution Cipher is simply the replacement of a character with something else. It could be with another Letter, Number, Symbol, sound, picture ... etc.

Substitution Ciphers can also be classified into 4 major types with each having many variations

1. Simple Substitution (Monoalphabetic) - Which uses only one cipher alphabet

2. Multiple-Alphabetic Substitution (Double-Key, Polyalphabetic) - Uses several different cipher alphabet

3. Polygram Substitution - Uses groups of letters which are replaced with other groups of letters. Again these could be letters or numbers

4. Fractional Substitution - Uses a certain type of cipher alphabet, and breaks up the substatutes for single letters and then subjects these fractions to futher encipherment.

Firstly we will look at a letter number cipher. This is something that we ran into this year at DefCon with the badge challenge and I thought it would be a good place to start This cipher replaces letters with numbers, for instance A=1, B=2, .... Z=26. Each Letter in the alphabet equates to a number. You may see these also in 2 digit form like A=01, B=02... etc.

Lets take this example:
20-8-9-19 9-19 1 13-5-19-19-1-7-5
Using a pencil and paper we can map out the alphabet to numbers:

Writing it down
Then we can solve the cipher: "This is a message" by matching up the Numbers to the letters in the above image.

Practical Experience:
Ok, now take out your pencil and paper, map out the alphabet as we did above and match up the following code:

06-09-22-05 25-05-01-18-19 15-06 19-05-03-11-03

Send me the decrypted message via email to flightgod at gmail dot com or message @fg in seckc slack to solve the puzzle.

Different Styles: