In response to question 3, I believe that examples of cryptography noted in Singh chapter 1 were mainly of monarchs and leaders because the information they trade is far more dangerous and powerful than information traded by those who weren't involved in the politics of the world. For example, when the Greeks defended themselves against the Persians using the wax tablets from Demaratus, the lives of all the people of Ancient Greece would have been affected by the Persian naval attack, and hypothetical subsequent takeover. In fact, that could have rewritten history! However, Leonidas was a leader of Ancient Greece, which is why they were encountering such sensitive information and therefore were more motivated to develop more effective methods of stenography. (Kahn) In contrast, I can think of an example where perhaps two peasants wanted to communicate with each other, yet had to do so in secret because of a family feud, inappropriate relationship, etc. Since they are communicating on a much smaller scale, their cryptographic practices may not appear as developed as the Greeks or Mary's because the consequences of the message being intercepted would not be as far-reaching. I don't believe this has changed over time because as of now, we have even more sensitive information to deal with, such as nuclear weapons and troop deployment. This provides the government an even greater incentive to create difficult ciphers and keep certain knowledge a secret. Yet, in the textbook the Greek victory was won over the Persians because the people of Greece had received notice about these secret messages. In our society, we do not have unlimited access to the messages our government intercepts. Is it the duty of the government to share the messages they decipher to us as citizens? With the technology we possess today there would almost definitely be word sent to a possible enemy that their code has been broken, which may lead to even more advanced ciphers which the government would be unable to break, and left rendered unable to defend us as citizens. Clearly, there is a difference in the types of cryptography and stenography used in the times of Ancient Greece and Medieval England, but the governments still remain the most sophisticated of cryptanalytics due to the content of the messages they receive.
Citations: Kahn D. (1996) The history of steganography. In: Anderson R. (eds) Information Hiding. IH 1996. Lecture Notes in Computer Science, vol 1174. Springer, Berlin, Heidelberg