Please enable JavaScript.

Coggle requires JavaScript to display documents.

15 Cryptographic Services, 15.1.3 Data Integrity, 15.1.4 Data…

- - - - There are three primary objectives of securing communications:
        
        Authentication - This guarantees that the message is not a forgery and actually comes from the authentic source. Modern networks ensure authentication using hash message authentication code (HMAC).
        
        Integrity - This guarantees that no one intercepted the message and altered it; similar to a checksum function in a frame. This is provided by implementing the SHA-2 or SHA-3 family of hash-generating algorithms.
        
        Confidentiality - This guarantees that if the message is captured, it cannot be deciphered. This is provided using symmetric or asymmetric encryption algorithms.
- - - - Enigma machine
      - Vigenère cipher
      - CAESAR CIPHER
      - SCYTALE
    - - plaintext message
      - Encryption Process
      - Encrypted Message
    - - Substitution ciphers substitute one letter for another. In their simplest form, substitution ciphers retain the letter frequency of the original message.
        
        The Caesar cipher was a simple substitution cipher.
        Because the entire message relied on the same single key shift, the Caesar cipher is referred to as a monoalphabetic substitution cipher. It is also fairly easy to crack. For this reason, polyalphabetic ciphers, such as the Vigenère cipher, were invented. The method was originally described by Giovan Battista Bellaso in 1553, but the scheme was later misattributed to the French diplomat and cryptographer, Blaise de Vigenère.
    - - The Vigenère cipher is based on the Caesar cipher, except that it encrypts text by using a different polyalphabetic key shift for every plaintext letter. The different key shift is identified using a shared key between sender and receiver. The plaintext message can be encrypted and decrypted using the Vigenère Cipher Table that is shown in the figure.
        
        The F (FLANK) is encoded by looking at the intersection of column F and the row starting with S (SECRETKEY), resulting in the cipher letter X.
        
        The L (FLANK) is encoded by looking at the intersection of column L and the row starting with E (SECRETKEY), resulting in the cipher letter P.
        
        The A (FLANK) is encoded by looking at the intersection of column A and the row starting with C (SECRETKEY), resulting in the cipher letter C.
        
        The N (FLANK) is encoded by looking at the intersection of column N and the row starting with R (SECRETKEY), resulting in the cipher letter E.
        
        The K (FLANK) is encoded by looking at the intersection of column K and the row starting with E (SECRETKEY), resulting in the cipher letter O.
    - - Gilbert Vernam was an AT&T Bell Labs engineer who, in 1917, invented, and later patented, the stream cipher. He also co-invented the one-time pad cipher. Vernam proposed a teletype cipher in which a prepared key consisting of an arbitrarily long, non-repeating sequence of numbers was kept on paper tape, shown in the figure. It was then combined character by character with the plaintext message to produce the ciphertext.
- - - - Cryptology is the science of making and breaking secret codes. As shown in the figure, cryptology combines two separate disciplines:
      - Cryptography - the development and use of codes
      - Cryptanalysis - the breaking of those codes
      - There is a symbiotic relationship between the two disciplines because each makes the other one stronger. National security organizations employ practitioners of both disciplines and put them to work against each other.
      - There have been times when one of the disciplines has been ahead of the other. For example, during the Hundred Years War between France and England, the cryptanalysts were leading the cryptographers. France mistakenly believed that the Vigenère cipher was unbreakable, and then the British cracked it. Some historians believe that the successful cracking of encrypted codes and messages had a major impact on the outcome of World War II. Currently, it is believed that cryptographers are in the lead.