17.1 Encryption, Encryption Protocols and Digital Certificates

Encryption

• Encryption is the process of converting data into an unreadable form to prevent unauthorized access.
• Plaintext: Original text
• Ciphertext: Encrypted Text
• Public key: Publicly available key that is used to encrypt message
• Private Key: Key only known to owner used to decrypt data encrypted with corresponding public key
• Symmetric Encryption/Symmetric Key Cryptography:
  • Same key is used for both encrypting and decrypting
  • Key must be shared securely in advance
• Asymmetric Encryption/Asymmetric Key Cryptography:
  • Uses a public key and a private key
  • The sender encrypts the message with the receiver’s public key
  • Data is decrypted using the private key

Quantum Cryptography

Uses the properties of photons to create an encryption system that is extremely difficult to break.

Secure Socket Layer (SSL)/Transport Layer Security (TLS)

Purpose of SSL/TLS

• Provide a secure communication channel between client and server over the internet
• Ensures
  • Authentication: Verifies that the server (and sometimes client) is genuine.
  • Encryption: Data is scrambled so attackers cannot read it.
  • Integrity: Ensures data is not altered during transmission.
• TLS is the updated, more secure version of SSL.

SSL/TLS in client-server communication

• Used in HTTPS (HyperText Transfer Protocol Secure).
• Used in client-server application by the use of encryption and using digital certificates
• Process:
  • Client (browser) sends a request to server to initialize a SSL/TLS connection
  • The session begins with a handshake.
  • Server responds by sending its digital certificate
  • Client verifies the certificate through a Certificate Authority (CA)
  • Client generates a session key and encrypts it using server’s public key
  • The session key is sent to server and it is used for encrypting and decrypting all the data that is transferred between the two nodes

Uses of SSL/TLS

• Online banking
• E-commerce sites
• Email communication
• Cloud storage/file transfer
• Login pages

Digital Certificate

• An electronic document verifying the identity of an entity
• Contains
  • Unique serial number of the certificate
  • Certificate Authority (CA) that issued the certificate
  • Certificate Authority that issued the digital signature
  • Name of the company, organization, individual, or owner of the certificate
  • Validity period of the certificate (start and end dates)
  • Public key
  • Hashing Algorithm

Acquiring Digital Certificate

• The user starts an application for a digital certificate on their computer.
• A key pair (public key and private key) is generated on the user’s computer.
• The user submits the application to the Certificate Authority (CA), sending the public key and other required data, encrypted with the CA’s public key.
• The CA creates a digital certificate containing all necessary details and signs it using the CA’s private key.
• The CA sends the completed digital certificate back to the user.

Digital Signature

• Sender’s side
  • Hash the message to produce a digest.
  • Encrypt the digest with the sender’s private key, this creates the digital signature
  • Send the message along with the digital signature to the receiver
• Receiver’s side
  • Receive the message and digital signature
  • Decrypt the digital signature with the sender’s public key to recover the original digest.
  • Hash the received message using the same algorithm to create a new digest
  • Compare the two digests:
    • If they match, the message is authentic and untampered.
    • If there is a mismatch, the message has been altered.