Certified Information Systems Security Professional (CISSP) Practice Exam

The purpose of a cryptographic method like the book cipher is to use known texts for secure message encoding. In a book cipher, both the sender and receiver use the same book or text as a key to encrypt and decrypt messages. The sender encodes the message by substituting words or letters with references to specific locations in the book (for example, page number, line number, or word number). This method relies on the shared knowledge of the chosen text to ensure that only the intended recipient, who has access to the same book, can decode the message.

This method emphasizes the uniqueness of the key (the chosen book), allowing for a more nuanced and context-dependent encoding compared to more straightforward encryption methods. While the book cipher can facilitate secure communication, its primary focus is on the use of a known text for encoding messages rather than enhancing authentication processes or ensuring non-repudiation. These other aspects are important in the broader field of cryptography but do not specifically pertain to the fundamental operation of a book cipher.