Readings: Cryptography Summary

Introduction to Cryptography

• Cryptography requires two steps: encryption and decryption. The encryption process uses a cipher in order to encrypt plaintext and turn it into ciphertext. Decryption, on the other hand, applies that same cipher to turn the ciphertext back into plaintext.

• Encryption: scrambling the data according to a secret key (in this case, the alphabet shift).
• Decryption : recovering the original data from scrambled data by using the secret key.

• Code cracking : uncovering the original data without knowing the secret, by using a variety of clever techniques.

• Types of Cryptography :
  1. Hashing : Hashing is a type of cryptography that changes a message into an unreadable string of text for the purpose of verifying the message’s contents, not hiding the message itself.
  2. Symmetric Cryptography: This type of cryptography uses a single key to encrypt a message and then decrypt that message upon delivery.
  3. Asymmetric Cryptography :Asymmetric cryptography (as the name suggests) uses two different keys for encryption and decryption, as opposed to the single key used in symmetric cryptography. The first key is a public key used to encrypt a message, and the second is a private key which is used to decrypt them.
  4. Key Exchange Algorithms
• The 4 Types of Cryptographic Functions :
  1. Authentication
  2. Nonrepudiation
  3. Confidentiality
  4. Integrity: The most common way to do accomplish data integrity through cryptography is by using cryptographic hashes to safeguard information with a secure checksum.

Ceasar Cipher :

• In cryptography, a Caesar cipher, also known as Caesar’s cipher, the shift cipher, Caesar’s code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions down the alphabet.

• The Caesar cipher can be easily broken even in a ciphertext-only scenario. Two situations can be considered:
  • an attacker knows (or guesses) that some sort of simple substitution cipher has been used, but not specifically that it is a Caesar scheme;
  • an attacker knows that a Caesar cipher is in use, but does not know the shift value.
• Example :
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