Information Assurance and Security chapter two-part 1.pptx

teaching notes about cryptography

1. Chapter 2 Brief overview of Commercial Issues on Security

2. Introduction Human being from ages had two inherent needs: To communicate and share information and To communicate selectively. These two needs gave rise to the art of coding ( encrypting ) the messages. Only the intended people could have access to the information . Unauthorized people could not extract any information, even if the scrambled messages fell in their hand.

3. Modern cryptography provides the following security services: Confidentiality – Ensuring that no one can read the message except the intended receiver. Integrity - Ensuring that information cannot be altered in a way from the original. Non-repudiation –A mechanism to prove that the sender really sent the message. Authentication - Ensuring that the Sender and receiver can confirm each.

4. In general there three types of cryptographic techniques: Symmetric-key cryptography Hash functions. Public-key cryptography 1. Symmetric-key Cryptography : Both the sender and receiver share a single key. The sender uses this key to encrypt plaintext and send the cipher text to the receiver. On the other side the receiver applies the same key to decrypt the message and recover the plain text.

5. 2. Public Key Cryptography Symmetric Key Cryptography require both parties to share a common secret key. The major problem with symmetric cryptography is that the process of transferring keys to the recipient is prone to security risks. Often a secure system failure occurred due to a break in the key distribution technique. To address the security issues posed by symmetric key cryptography . Public Key /asymmetric Cryptography solves the problem of single key cryptography by using a pair of keys instead of a single key . .

6. public-key : which may be known by anybody, and can be used to encrypt messages private-key , known only to the recipient, used to decrypt messages , In public key cryptography, the data that is encrypted with the public key can only be decrypted with the corresponding private key . is asymmetric because those who encrypt messages cannot decrypt messages . Public-Key algorithms use one key for encryption and a different but related key for decryption .

7. Important characteristics Public key cryptography It is computationally infeasible to find decryption key(Private key) knowing only algorithm & encryption key. It is computationally easy to en/decrypt messages when the relevant (en/decrypt) key is known.

8. The steps involved in a public-key encryption are given below: 1 .) Each user generates a pair of keys to be used for encryption and decryption. 2 .) Each user places one of the two keys in a public register and the other key is kept private. 3 .) If Bob wants to send a confidential message to Alice, Bob encrypts the message using Alice’s public key.

9. 4 .) When Alice receives the message, she decrypts the message using her private key . 5 .) If a user wishes to change his keys –generate another pair of keys and publish the public one: no interaction with other users is needed.

10. In a public key cryptography, each participant has a pair of public and a private keys.

11. 3. Hash Functions : A hash function is a mathematical function or algorithm that takes a variable number of characters (called a ”message”) and converts it into an output with a fixed number of characters (called a hash value or simply, a hash ). No encryption key is used in this algorithm. Hash functions are used by many operating systems to encrypt passwords.

12. Hash Function 12 …M… H (M) Hash Function H Message of arbitrary length Fixed length output 10/22/2025

13. Key Highlights about hash function A hash function is a mathematical function that converts any data into an output string with a fixed number of characters. Hashing is generally a one-way function , which means that it is easy to convert a message into a hash but very difficult to “reverse hash” a hash value back to its original message. Hashing is useful to ensure the authenticity of a piece of data b/c even a small change in the message will create an entirely different hash .

14. Why Do We Need Hash Functions? 1. Standard Length When you hash a message, it takes a file or message of any size, runs it through a mathematical algorithm, and produce an output of a fixed length. Table 1: Different Hash Functions

15. It doesn’t matter what we put in as an input, the same hash function will always produce a hash value that has the the same number of characters. Table 2: Different Inputs Using the Same Hash Function (SHA-1)

16. 2. Ensure data integrity Let’s think of an example where you want to send a digital message or document to someone, and you want to make sure that it hasn’t been tampered with along the way. You could send it multiple times and have the recipient verify each copy is the same, but that would not be feasible if the file or message was very large. It would be much easier if there was a way of having a shorter and set number of characters for the sender and receiver to check. And that’s essentially what a hash function allows two computers to do. Hash functions, therefore, serve as a check-sum or a way for someone to identify whether digital data has been tampered with after it’s been created.

17. 3. Verify authenticity For example, if you send out an email, it can be intercepted easily . The recipient of the email has no way of knowing if someone has altered the contents of the email along the way, called a fabrication attack. However, if the sender signs the email with their  digital signature   and hashes that together with the email contents, the receiver can examine the hash data to ensure that the email contents have not been modified after being digitally signed. To do this, the receiver would compare the hash value on the digitally-signed email received to a hash value they “re-generate” themselves using the same hash function provided by the sender, as well as the signer’s public key. If it matches, that means that no one has altered the message, but if the hashes are different, then the receiver knows that the contents of the email are not authentic, as even if something small has been changed in that message, the hash will be completely different.

18. Examples of Common Hash Functions: The SHA-256 function: short for “Secure Hash Algorithm” and was designed by the United States National Security Agency (NSA) and includes SHA-1, SHA-2 ( a family that includes SHA-224, SHA-256, SHA-384, and SHA-512), and SHA-3 (SHA3-224, SHA3-256, SHA3-384, and SHA3-512 ). Message Digest (MD) Algorithm : MD2, MD4, MD5, and MD6. MD5 was considered a hashing algorithm, but it’s now considered broken because of hash collisions (different input produce same hash) Rivest ­ Shamir ­Adelman (RSA) Generally speaking, the most popular hashing algorithms or functions have a hash length ranging from 160 to 512 bits.