The Dark Cave

Deep below The Village...

The cipher is said to be named after Julius Caesar who is thought to have used this to communicate with his army.

It is an example of a substitution code.

To secure his message he shifted the letters of the alphabet and sent what looked like scrambled text to those who did not know the key. The intended recipients knew the letter-shift algorithm and could easily decipher the message once they knew how many letters to shift for the key.

The plain text message "Veni vidi vici" is encoded to "Oxgb obwb obvb". The letter shift algorithm key is 7 - the letters have been moved 7 spaces. To decode the message the letters have to be moved 7 spaces.

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 T U V W X Y Z A B C D E F G H I J K L M N O P Q R S

Sometimes the keys for substitution ciphers were based on phrases known only to the sender and recipient. One could be the pangram "The quick brown fox jumps over the lazy dog". Using only the first occurrence of each letter gives us:

T H E Q U I C K B R O W N F X J M P S V L A Z Y D G

A quick substitution gives the following:

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 T H E Q U I C K B R O W N F X J M P S V L A Z Y D G

Where A in plaintext is encoded to T, B becomes H, C becomes E, D becomes Q etc. The bottom row of letters could be randomised or shifted or scrambled to add another complication.

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 X N F T G H D E Y Q Z U A I L C V K S B P R M O J W

Although these are fun, they are not very secure. In the world of intellegence, banking, computer science etc. more advanced encryption is needed to secure secrets. We use these in everyday life, often without realising it, for example our PIN number for banking, or the password for our computer.

Look at the section about Frequency Analysis to discover how easy it is to crack this type of cipher.