DPEFT, DJQIFST boe TFDSFU XSJUJOH.

If for each letter, you instead write the letter before it in the alphabet, you will discover what we are doing this morning.

DPEFT, DJQIFST boe TFDSFU XSJUJOH. becomes CODES, CIPHERS and SECRET WRITING.

WHY? Codes have been important throughout history. Thousands of people were employed during the second world war at Bletchley Park, trying to decipher the codes that were sent by the Germans to each other. If they could decipher the code, they could sink their ships.

WHEN? Codes have been used since humans could write. The Romans used to send messages throughout their empire using codes to which only they had the key.

HOW? Only trusted friends who have the code’s key can crack the code and read the message.

CODE 1: SHIFT CIPHER You previously saw the example of the SHIFT CIPHER, it gives each letter in the code a different letter in real life. The rule is the alphabet is SHIFTED one way or another but stays in the same order. My cipher was:

CODE 1: SHIFT CIPHER ABCDEFGHIJKLM BCDEFGHIJKLMN NOPQRSTUVWXYZ OPQRSTUVWXYZA The TOP line is what the letter actually is, the BOTTOM line is the one you write in the code.

The letters were moved one place to the left.

Design your own SHIFT CIPHER You ‘move’ the alphabet along as many places as you like but it must be in the same order. SEND this message, to a friend, using your shift cipher. How many fives in ten SEND your own message. Can a partner decode it?

CODE 1: SHIFT CIPHER ABCDEFGHIJKLM NOPQRSTUVWXYZ The TOP line is what the letter actually is, the BOTTOM line is the one you write in the code.

BREAKING THE SHIFT CIPHER Generally not very reliable. If you can work out one letter (like the e, which will occur most often over a long message) then you can work out all the other letters as well.

CODE 2: KEY WORD CIPHER Works in a similar way. The letters are arranged in order, except the letters from the key word are taken out and put at the beginning. NOTE: the key word must NOT have any repeating letters.

KEY WORD = FOREST ABCDEFGHIJKLM FORESTABCDGHI NOPQRSTUVWXYZ JKLMNPQUVWXYZ The TOP line is what the letter actually is, the BOTTOM line is the one you write in the code.

DESIGN your own KEY WORD cipher and write a short message for a trusted partner to decipher. You ONLY need to tell them the KEY WORD, they should not need your CIPHER sheet.

The KEY WORD cipher is harder to break than the SHIFT cipher. The next cipher is even harder to break. This is because the letters can be in any order.

Code 3: The Pigpen Cipher Devised in 1640 (during the English Civil war) Looks like pigs in a pen

Here the letters are represented by a diagramatical code The dots are important, if you don’t use them then you will mix up K and X etc. Do not write the letter, just draw the sides and dots that are next to it. I A M A C O D E B R E A K E R

DESIGN your own Pigpen cipher and send a message to a friend asking how long it is until home time. Get them to use their own cipher in reply.

CODE 4: THE CREASE CODE Fold a blank piece of A4 paper into 6, so the fold marks are as below. Long side

Write your code on the CREASES

Fill the rest up to make other words, it is better if they make sense. B i aG g O r E a pleas poa hed Is n t elightfula M al

BONUS CODE: ALBERTI’S DISC You need 2 discs where one overlaps the other. The inside is the letter you write down the outside is the real letter (the translation) Mix the letters up, as you like. Your partner needs to know the starting point. After each letter is translated, turn the inner disc one position clockwise. Then repeat by translating the next letter and so on. Very difficult to break.

CODE 5: WORD GRILLES These look like a series of random words until a grille is put over the top to make sense. WATCH

LAST FINAL HALF MONKEY GIRAFFE CIPHER JUMBLE GOAT COAT HAT PLEASE FOUND GET REHEARSE HOME AWAY LIGHT DARK HOUR CODE OBVIOUS ANSWER TIME FIND