7. The Bedrock of Cybersecurity: Cryptography 155 Table 7.5 A partial codebook. Codebooks essentially create a new language. A famous example of a codebook actually used a real language: the Navajo Code Talkers. During World War II, English bilingual Navajos used their native language to communicate military messages over the radio waves. Because of the open nature of the radio spectrum their messages were intercepted by enemy forces, but the enemy was never able to successfully decode them. The Navajos substituted some of their native words for modern military terms, such as “buzzard” for “bomber” and “iron fish” for “submarine.” Because the structure of their language is unusual and is spoken by so few people, it was an ideal spoken codebook—enemy forces had trouble isolating words and could not identify the language nor translate it. One enormous advantage of this technique was its practicality and efficiency. Code Talkers could be trained easily and messages could be encrypted and decrypted quickly as Navajos translated in their heads in real time. 7.1.3 Letter and Word Transposition “A few weeks earlier, Manton Marble, one of Tilden’s closest political advisors, had written an open letter to the New York Sun contrasting dark Republican practices with Tilden’s station in ‘the keen bright sunlight of publicity.’ Whitelaw Reid, the Tribune’s brilliant editor...inserted the cipher telegrams in editorials as subtle commentaries on Marble’s letter.” - The Codebreakers by David Kahn Substitution at the level of letters and words is not the only mechanism for creating cryptographic schemes. In addition to substitution, cryptography can also be employed with transposition. Transposition is the rearranging of plaintext letters or words to transform them into ciphertext. Table 7.6 shows a double transposition cipher. The plaintext message is written out in a template table, filling it from left-to-right and top-to-bottom. Then the columns and rows of the table are rearranged and the result is written out to produce ciphertext. The size of the template table and the permutation of the columns and rows is the key. In the example, the key is BDCA321 and attack at dawn is transformed into ANWDKTACTATA. In this scheme, the letters are not disguised, but the underlying language pattern is.
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