What is Message Authentication?
- Is a piece of information used to authenticate a message
- Protects against active attacks
- Verifies that a message is authentic
- Contents is not altered– comes from a reliable source
- Timely and in a correct sequence
- Receiver performs same computation on message and checks that it matches the MAC
- Only sender & receiver share a key
Hash Function Requirements
- A group of characters (keys) that maps onto a hash value and compares it to a the receiver with the message.
- If both hash values are the same, the message is authenticated.
Two approaches to attacking a secure hash function and the additional secure hash function applications
- Cryptanalysis
Exploits logical weakness in an algorithm
- Brute-Force attack
Strength of hash function depends on the length of the hash code produced
Additional secure hash function applications:
- Passwords
- Hash function stores is the OS
What is Public-Key Encryption Structure?
- Based on mathematical functions
- Asymmetric
- Uses two separate keys – PUBLIC and PRIVATE
- Public made “public” for others
- Protocol needed: **Key distribution **
Public key 6 ingredients of Asymmetric
Plaintext – Readable message fed into the algorithm
- *Encryption algorithm** – Transformation from plaintext
- *Public** and
- *Private key** – Pair of keys for encryption and decryption
- *Ciphertext** – Scrambled message produced as an output
- *Decryption algorithm** – produces the original plaintext
Requirements of public-key Cryptosystems
- Computationally easy to create key pairs
- Sender knowing the public key to encrypt messages
- Receiver knowing the private key to decrypt ciphertext
- Computationally infeasible
- For opponent to determine the private key from public key
- For opponent to **recover original message **
Asymmetric Encryption Algorithm
- Enables two users to securely agree about a shared secret that can be used as a secret key for subsequent symmetric encryption of messages
- Limited exchange of the keys
What is Digital Signature Standard and Elliptic Curve Photography?
Digital Signature Standard (DSS)
Provides a digital signature function
Cannot be used for encryption or key exchange
Elliptic Curve Photography (ECC)
Security like RSA but with smaller keys
What is Digital Signature?
- is a mathematical technique used to validate the authenticity and integrity of a message/source
- Attach a code that acts like a signature
- Identity of an electronic document/message** **and acknowledging the signer for consent
- Encrypts hash code with private key
- Does not provide confidentiality
- When there is a complete encryption
- Message is safe from **alteration **
Digital Envelops
- Does not require having the same key to protect a message arranged by the sender and receiver
- Equates to the same as “sealing an envelope containing a unsigned letter”
Random Numbers
Uses generation of:
- Keys for public-key
- Stream key for symmetric stream cipher
- Symmetric key used as a temporary session key or creating a digital envelope
- Handshaking to prevent replay attacks
andom VS Pseudorandom
Cryptographic applications make use of algorithmic techniques for random number generation
What are Pseudorandom?
- Sequences to produce to satisfy the statistical randomness tests
- Likely to be predicable
What is aTrue Random Number Generator?
- Uses nondeterministic source to produce randomness
- Operates by measuring unpredictable **natural processes **
Practical Application of encryption
- : Encryption of stored data
- Common to encrypt transmitted data
- Less common for encryption
- There is little protection beyond domain authentication and OS access controls
Approaches to encrypt stored data
- Uses commercially available encryption package
- Black-end appliance
- Library base encryption
List and describe three approaches to message authentication
- Message encryption
- Message authentication code
- Hash function
What properties must a hash function have to be useful for message authentication?
- Can be applied to a block of data of any size
- Produces a fixed-length output
- H(x) is easy to compute for a given x
How can public-key encryption be used to distribute a secret key?
- An approach is for the sender to encrypt a
secret key with the recipient’s public key.
Three ways in which a message can be authenticated using hash code
- Message can digest encryption using Symmetric Encrytion
- Can digest using public-key encrytion
- Using hash function but no encryption for message authentication
