Cryptanalysis has changed greatly over history in terms of difficulty and ability to be solved. According to Simon Singh “Cryptanalysis could not be invented until a civilization had reached a sufficiently sophisticated level of scholarship…” This is the case for two reasons: first, a civilization would need to have a very standardized written communication system before cyphering would even be necessary, as there is no practicality in encrypting a written language that no one understands to begin with. Second, as written languages began to become standardized, the lack of popular education in reading and writing, left cryptography to the only greatest scholars. Substitution cyphers could be relatively simple and still effectively conceal a message.
As education became more common, cyphers would need to be much more complex as more people could work on successfully decrypting. More modernly, as education has hit new levels along with the emphasis on critical thinking, a simple substitution cypher could be analyzed for common frequency patterns easily broken by a group of college freshmen (THAT’S US!).
Additionally, with the development of computers, new heights of complexity are introduced to cryptography. A simple common device such as a cell phone uses complex encryption that can ensure privacy for simple text messages, to creating secure lines for bank transactions. Not only have the creation of codes been revolutionized by computers, but the decryption of them have been improved just as much. Even complex substitution cyphers that would have left scholars thinking for days could be broken in seconds.
It is amazing how we take the complexity and convenience of encryption for granted as others in the past labored greatly to make a fraction of that security possible.