Chapter 5 2025

1. Asymmetric cryptography - Cryptography wherein two keys are used: one to encrypt the message and another to decrypt it. 2. Block cipher - A form of cryptography that encrypts data in blocks; 64-bit blocks are quite common, although some algorithms (like AES) use larger blocks. 3. Bruteforce attack - An attack in which the attacker tries to decrypt a message by simply applying every possible key in the key space. 4. Caesar cipher - The method of cryptography in which someone chooses a number by which to shift each letter of a text in the alphabet and substitute the new letter for the letter being encrypted. For example, if your text is "A CAT," and you choose to shift by two letters, your encrypted text is "C ECV." This is also known as a monoalphabet, single-alphabet, or substitution cipher. 5. Carrier - The signal, stream, or data file into which the payload is hidden. 6. Channel - The type of medium used to hide data in steganography. This may be photos, video, sound files, or Voice over IP. 7. Cryptanalysis - A method of using techniques other than brute force to derive a cryptographic key. 8. Euler's Totient - The total number of coprime numbers. Two numbers are considered coprime if they have no common factors. 9. Feistel function - A cryptographic function that splits blocks of data into two parts. It is one of the most influential developments in symmetric block ciphers. 10. Kasiski examination - A method of attacking polyalphabetic substitution ciphers by deducing the length of the keyword. This is sometimes also called Kasiski's test or Kasiski's method. 11. Keyspace - The total number of keys. 12. Least significant bit (LSB) - The last bit or least significant bit is used to store data. 13. Payload - The data to be covertly communicated. In other words, it is the message you want to hide. 14. Social engineering - Nontechnical means of obtaining information you would not normally have access to.