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Module 15: Cryptographic Services, image, image, image, image, image,…
Module 15: Cryptographic Services
15.1 Secure Communications
15.1.1 Authentication, Integrity, and Confidentiality
The network administrator’s first goal is to secure the network infrastructure, including routers, switches, servers, and hosts.
15.1.2 Authentication
Authentication guarantees that a message comes from the source that it claims to come from.
15.1.3 Data Integrity
With data integrity, the receiver can verify that the received message is identical to the sent message and that no manipulation occurred.
15.1.4 Data Confidentiality
This can be achieved through encryption. Encryption is the process of scrambling data so that it cannot be easily read by unauthorized parties.
15.2 Cryptography
15.2.1 Creating Cipher Text
Messengers from a king’s court took encrypted messages to other courts.
Scytale
A strip of paper or other material is wrapped around a rod of a known diameter
Caesar Cipher
The Caesar Cipher is a type of substitution cipher in which each letter is replaced by another letter that is a set number of places away in the alphabet.
Vigenère cipher
is a type of polyalphabetic substitution cipher. It was considered unbreakable until 1863.
Enigma machine
was an electromechanical encryption device that was developed and used by Nazi Germany during World War II.
15.2.2 Transposition Ciphers
Plaintext message
Encryption Process
Encrypted Proccess
15.2.3 Substitution Ciphers
plaintext message
Encryption Process
Encrypted Proccess
15.2.4 A More Complex Substitution Cipher
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.
15.2.5 One-Time Pad Ciphers
Gilbert Vernam was an AT&T Bell Labs engineer who, in 1917, invented, and later patented, the stream cipher.
15.3 Cryptanalysis
15.3.1 Cracking Code
Cryptanalysis is the practice and study of determining the meaning of encrypted information (cracking the code), without access to the shared secret key.
15.3.2 Methods of Cracking Code
Brute-force method - The attacker tries every possible key knowing that eventually one of them will work.
Ciphertext method - The attacker has the ciphertext of several encrypted messages but no knowledge of the underlying plaintext.
Known-Plaintext method - The attacker has access to the ciphertext of several messages and knows something about the plaintext underlying that ciphertext.
Chosen-Plaintext method - The attacker chooses which data the encryption device encrypts and observes the ciphertext output.
Chosen-Ciphertext method - The attacker can choose different ciphertext to be decrypted and has access to the decrypted plaintext.
Meet-in-the-Middle method - The attacker knows a portion of the plaintext and the corresponding ciphertext.
15.3.3 Cracking Code Example
When choosing a cryptanalysis method, consider the Caesar cipher encrypted code. The best way to crack the code is to use brute force.
15.4 Cryptology
15.4.1 Making and Breaking Secret Codes
Cryptology is the science of making and breaking secret codes.
15.4.2 Cryptanalysts
Cryptanalysis is often used by governments in military and diplomatic surveillance, by enterprises in testing the strength of security procedures, and by malicious hackers in exploiting weaknesses in websites.
15.4.3 The Secret is in the Keys
In the world of communications and networking, authentication, integrity, and data confidentiality are implemented in many ways using various protocols and algorithms.
