1.1. ANCIENT TIMES 3 the secret formula for a glaze for pottery, where the figures defining the ingredients were purposefully jumbled so people couldn’t steal the secret recipe for the pottery glaze. This is the oldest known surviving example of encryption. As important as pottery is to some, when cryptography is mentioned people think of spies and military secrets, not pottery glazes. The first documented use of secret writing by spies occurred in India around 500 BCE. The Indians used such techniques as interchanging vowels and consonants, reversing letters and aligning them with one another, and writings placed at odd angles. Women were expected to understand concealed writings as an important skill included in the Kama Sutra. The Old Testament of the Bible includes an account of Daniel. He was a captive of Babylon’s King Nebuchadnezzar around 600 BCE and had won promotion with successfully interpreting one of the king’s dreams. He saw a message “Mene, Mene, Tekel, Parsin” written on a wall (Daniel 5:5–28) and interpreted it as Mene meaning “God Hath numbered thy kingdom and finished it” Tekel as “Thou art weighed in the balances and art found wanting” and Parsin as “Thy kingdom is divided and given to the Medes and Persians”. The king was killed that very night and Babylon fell to the Persians. Other passages of the Old Testament allude to passwords required for entry into various places. Very few knew the passwords, or keys as they were often called. As time progressed and conflict became more prevalent and important to the spread of boundaries, the need for concealed messages grew. This was also at a time when written records began to be collected. Both the Greeks and the Persians used simple encryption techniques to convey battle plans to their troops in the fifth century BCE. For example, one technique was to wrap a missive written on parchment around rods of specific sizes and with writing down the length of the rod. When unwrapped the letters were not in the right order, but wound around the right size rod they were. Another example is the Greek use of wooden tablets covered with wax to make them appear blank (a steganographic technique discussed in Chapter 10), which were then decrypted by melting the wax to expose the written letters. Various transmission systems were developed to send messages in the period between 400 and 300 BCE, including the use of fire signals for navi- gation around enemy lines. Polybius, the historian and cryptographer, ad- vanced signaling and cipher-making based on an idea of the philosopher Democritus. He used various torch signals to represent the letters of the Greek alphabet, and he created a true alphabet-based system based on a 5 × 5 grid, called the Polybius checkerboard. This is the first known system to transform numbers to an alphabet, which was easy to use. Table 1.1 shows a Polybius checkerboard (note that i and j are indistinguishable): Each letter is coded by its row and column in that order for example s is coded as 43. The word “spy” would be coded by 43, 35, 54, while “Abe is a spy” is 11, 12, 15, 24, 43, 11, 43, 35, 54. It’s easy to decode: all we have to
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