Unit 3: Asymmetric Key Algorithm and RSA

Digital Signature and Encryption

• Digital signature provides non-repudiation of message, message authentication, and data integrity.
• Digital signature ensures that sender cannot deny sending the message.
• Digital signature is used in public-key primitives of message authentication.
• Digital signature binds a person/entity to digital data, which can be independently verified by receiver and third party.

Encryption with Digital Signature

• Encryption with digital signature provides confidentiality, authentication, integrity, and non-repudiation.
• There are two methods to combine digital signature with encryption: sign-then-encrypt and encrypt-then-sign.
• Encrypt-then-sign is a more reliable method, where receiver verifies the signature using sender's public key and then decrypts the data using private key.

Knapsack Encryption Algorithm

• Knapsack encryption algorithm is a public key cryptography algorithm developed by Ralph Merkle and Mertin Hellman in 1978.
• It uses two different keys: public key for encryption and private key for decryption.
• Easy knapsack problem is used as private key and hard knapsack problem is used as public key.

Asymmetric Key Algorithm

• Asymmetric key algorithm uses two separate keys for encryption and decryption.
• Public key is used for encryption and private key is used for decryption.
• Advantage of asymmetric key algorithm is easier key distribution and integrity of message.
• Disadvantage of asymmetric key algorithm is slower due to multiple keys.

RSA Algorithm

• RSA algorithm is a public key encryption technique that uses prime numbers for security.
• RSA algorithm has two sets of keys: private key and public key.
• RSA algorithm is used for key exchange, email security, web security, and encryption systems.

Symmetric and Asymmetric Key Cryptography

• Symmetric key cryptography uses the same secret key for encryption and decryption.

• Asymmetric key cryptography uses a pair of keys: public key for encryption and private key for decryption.

• Symmetric key cryptography is faster and more efficient, but it has a key distribution problem.

• Asymmetric key cryptography is more secure, but it is slower and more complex.### Asymmetric Encryption

• Uses public and private keys for encryption and decryption

• Digital signatures verify the validity and credibility of a message, software, or digital record

• Provides proof of origin, identification, and status of an electronic record, transaction, or post

Applications of Asymmetric Encryption

• Encrypted email: uses public key to encrypt a file and private key to decode it
• SSL/TLS cryptographic protocols: provides encrypted connections between websites and browsers
• Bitcoin and other cryptocurrencies: public keys for transactions and private keys for security
• Each unspent transaction output (UTXO) in the Bitcoin ledger is associated with a public key

Advantages of Asymmetric Encryption

• No need to exchange keys, eliminating the key distribution issue
• Improved security: private keys are never exchanged or exposed to others
• Provides digital signatures that can be revoked
• Message verification ensures the sender's authenticity and prevents message alteration

Disadvantages of Asymmetric Encryption

• Slow speed compared to symmetric key encryption
• Authentication of public keys is required to ensure they belong to the intended individual
• Consumes more computer resources than symmetric key encryption
• Loss of a private key can be irreversible

Asymmetric Key Cryptography vs. Symmetric Key Cryptography

• Asymmetric key cryptography uses public and private keys
• Symmetric key cryptography uses a single key for encryption and decryption
• Asymmetric key cryptography is more complex and time-consuming
• Key lengths: symmetric (128 or 256 bits), asymmetric (2048 bits or higher)

Digital Signatures

• Bind a person/entity to digital data
• Use public-key cryptography and a secret key known only to the signer
• Ensure the sender cannot repudiate the origination of the message
• Digital signature scheme based on public key cryptography

Model of Digital Signature

• Each person has a public-private key pair
• Private key is used for signing, and public key is used for verification
• Hash value and signature key produce the digital signature
• Verification algorithm compares the output with the hash value to verify the signature