The History of Encryption

Instructor: Louay Chebib
Did you know that modern data encryption has roots that can be traced back almost 4,000 years? Encryption works equally well for military secrets and trade secrets as it does for love notes.

What Is Encryption?

Encoding is the process of converting something in the physical world into a representation that can be stored or shared. Just as a photograph encodes what is seen, letters and words encode ideas and what is heard into a format that can be stored or shared. The goal of encoding is to deliver these ideas to their intended recipients. A person who does not understand the language, or does not know how to read it, will be unable to de-code the information.

Encryption allows a person to hide the meaning of information or messages in such a way that only those who know the secret method may read them. For a very long time, people have had many different reasons for wanting to hide information from others. The earliest historic examples were for hiding trade secrets, military secrets, and secret correspondences between spies and lovers. These same encryption principles are now used to safeguard your internet communications.

Encryption Throughout History

Encryption is based on cryptography. Cryptography is the art of hiding information to make it unreadable without special knowledge or a key. The earliest recorded examples include the use of non-standard hieroglyphs as a substitute for the hidden information, and the use of personal identification marks such as seals, emblems, or logos for authentication. The receiver of the sealed item would have a copy of the true mark to use to authenticate the one presented (these are the precursors of signature verification).

Seal Example

A Scytale scrambles the meaning of a message when someone writes messages on a strip of leather or parchment wrapped around a rod; this requires the receiver to have a rod of the same diameter to make the message legible.


An early substitution cipher know as ATBASH reverses the alphabet.

ATBASH Cipher:

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

A more powerful substitution substitutes one letter for another by shifting the alphabet by a known number of letters. To decipher the message, the receiver needs to know how many letters to shift the text.

Shifted by 4 Cipher:

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

Some substitution ciphers rely on other alphabets or symbols for letter substitution.

Other alphabets or symbols for letter substitution
other alphabets or symbols for letter substitution

Extra complexity can be derived from a combination of shifting and substitution of letters.

Shifted and Substituted Cipher:

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

Here you can see a device known as a cipher disk that uses letter substitution. Both sender and receiver need identical disks to read it.

Cipher Disk
cipher disk

A password provides a key or key-phrase as the template for the shifting or substitution of letters. A password or key may be used directly, or may be run through an algorithm to create a much stronger encryption key.

Another common method of encryption depends on hiding the text in a letter or larger work. The writer uses the cutout (Cardan grille), a template, or pattern to hide message inside non-meaningful information. The recipient needs to have the same cutout or template, or know the pattern to read the message.

Cardan Grille
Cardan Grille

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