A (Very) Brief History of Pre-Computer Cryptography, Part 2

This is the second part of a two-part article exploring the history of pre-computer cryptography. Part 1 focused on the period from the birth of cryptography some 4,000 years ago to the development of early transposition and substitution ciphers. Part 2 looks at the emergence of cryptanalysis under the Abbasid Caliphate and goes through the perfection of mechanical encryption mechanisms in the mid-20th century.
The Birth of Cryptanalysis
Because of its simplicity and strength, the substitution cipher dominated secret communication for most of the first millennium CE. However, new developments were brewing in the . . .