Privacy, How it was done in the olden days

Over the years, since man developed means of communication in form of languages and writing, protecting information has always being very important. 
Humans have developed several ways of hiding information from people they don't want access to such information. Such information can be religious, trade secrets etc. The Assyrians developed the Intaglio for protecting their trade secrets, the Egyptians developed Hieroglyphs as a way for the priests to communicate with the dead and writing down prayers, the Hebrews  developed the ATBASH system, while the Greeks developed Wound Tape and unlocking key for hiding special information.
In this article, we are going to look into the Hieroglyphs and Atbash systems.



HIEROGLYPHS
Hieroglyphs is a system of writing in which symbols are used to represent objects and ideas.
This system of writing was used by the ancient Egyptians as far back as 1900BC. It was believed to be the oldest form of writing.

The glyphs(representation) can be classified into two,
phonograms which are used to represent sounds and ideograms which are used to represent ideas and objects.

The arrangement of phonographs and ideograms gives the reader hint in determining the information represented. The phonograms always goes before the ideograms and it gives the reader the definitive category to which the word belonged. In this case, we can comfortably say that the phonograms are the encrption keys.

The hierogylyphs which lliterally translates the 'the language of the gods' were used by the priests in writing down prayers, magical text and importantly in preparing the tombs for the dead. Its was believed that these writings will guide the dead through the afterlife.

The use of this system of writing is not restricted to religious purpose. Official information and events of great importance are written down on stones and walls with this form of writing.

ATBASH

An ATBASH Cipher is a substitution cipher with a fixed key. Each character that is to be encoded is replaced with another character, depending on the key.
the name ATBASH is derived from how the encoding itself. It was derived from Hebrew Alphabet where the first letter 'Aleph' is replaced by the last letter 'Tav' and the second letter 'Beth' is replaced by second to last 'Shin'. By taking the first letter of supplies the name ATBASH. Basically, the encoding is derived by reverse writing the alphabet order.
ABCDEFGHIJKLMNOPQRSTUVWXYZ
ZYXWVYTSRQPONMLKJIHGFEDCBA

'Hello world' can easily be encrypted as 'svool dliow'
This form of encryption was used by the Hebrews as early as 500BC. One of the popular use of this encryption system was in the Bible, in the Book of Jeremeiah. Prophet Jeremiah used this encryption to refer to Babel(Babylon) as Sheshach in following chapters and Verses - 25:26, 51:1, and 51:41.

A modern use of this encryption system can implemented using a key. The key is number of alphabetical shift from which you start counting back from. From the first representation of the alphabet and its derivative, its obvious the key is 25.
Another derivative of the ATBASH encryption is the Affine Cipher. It uses a key that comprises of 2 characters, a and b. To encode, 'a' must be a coprime number with the length of alphabet and be can be any number. Encryption and decryption can be achieved with the mathematical formula
e(x) = (ax +b) mod m
d(x) = apow(-1)(x - b) mod m.

ATBASH and affine will give same encryption by setting 'a' and 'b' to be 25.