Codes and Ciphers

By the end of this session you will be able to:

Solution:

Decode messages using different ciphers

By the end of this session you will be able to:

Round 1- Texting Challenge

Examples

•927

•WAS/WAR

•2628

•BOAT/COAT

•4483

•GIVE/HIVE

Round 1- Texting Challenge

“9428 36 968 2255 2 74337 9484 66 5347?”

“2 25683!”

Round 1- Texting Challenge

Solution:

“9428 36 968 2255 2

“What do you call a

74337 9484 66 5347?”

sheep with no legs?”

“2 25683!”

“A cloud!”

• Example• Welcome to Leeds University• welcometoleedsuniversity• 24 letters long =• 6×4 or 2×12 or 3×8 or 2×12 or 1×24

• So write:

Round 2- Transposition Challenge

Round 2- Transposition Challenge

• Going the other way round:• ckatsoenaadekifepdlesbesr• 25 letters= 5×5• So write:

• Example• cbkhenlroreedwdtderlwowweaspirao• 32 letters long=• 1×32 or 2×16 or 4×8• So write:

Round 2- Transposition Challenge

• Challenge

trmsimhlatsledld1owslo5nosegcg

Round 2- Transposition Challenge

Round 2- Transposition Challenge

• Challenge

trmsimhlatsled1owslo5nosegcg• Answer:

Round 2- Transposition Challenge

t h e w o

r l d s s

m a l l e

s t d o g

i s 1 5 c

m l o n g

The world’s smallest dog is 15cm long

Round 3- Pencil Code

• Answer-• This code was used 2500 years ago by the Spartans in Ancient Greece.

Round 3- Pencil Code

Refreshment Break

This would be a good time to try to earn some bonus points with the Number Phrase Round!

• Practise Questions• 00010• 11111• 10011• 00101

Round 4- Binary Challenge

Round 4- Binary Challenge

Answer:Computers view everything as ones and zeroes!

Round 5- Error Checking Challenge

• error_checking_example.doc

Error Checking

1 0 1 1 1

0 1 0 1 0

1 0 1 0 1

0 1 1 1 1

0 1 1 1 1

Image from the 2006 Royal Institution Christmas Lectures

Image from the 2006 Royal Institution Christmas Lectures

The Final!Frequency Analysis

Frequency Analysis of Letters Used in the English Language

a

b

c

d

e

f g

h

i

j

k

l

m

n

o

p

q

rs

t

u

v

w

x

y

z

0

2

4

6

8

10

12

14

a b c d e f g h i j k l m n o p q r s t u v w x y z

Letter

Fre

quen

cy (

%)

Other handy hints when cracking codes:

• The most frequent two-letter words are OF, TO, IN, IT and IS

• The most frequent three letter words are THE, AND, FOR, ARE and BUT

• Half of all English words begin with A,O,S,T or W

• The best code crackers won’t give up and always want to find the answer. Often there is a reward for those who succeed.

The Solution !