B FOR 204 Lecture Notes - Lecture 10: Https, Certificate Authority, Digital Signature Algorithm
2 Jun 2018
School
Department
Course
Professor
BFOR 204
Fundamentals Information and Cybersecurity
Cryptography - III
Applications for public-key cryptosystems
• Public-key systems are characterized by the use of a cryptographic type of algorithm
with two keys, one held private and one available publicly
• Depending on the application, the sender uses either the sender’s private key, the
receiver’s public key, or both to perform some type of cryptographic function
Asymmetric algorithms - Encryption
• Encryption with asymmetric cryptography works in a slightly different way from
symmetric encryption.
• Someone with the public key is able to encrypt a message, providing
confidentiality, and then only the person in possession of the private key is able to
decrypt it.
Digital Signature standard (DSS)
• FIPS PUB 186
• Makes use of the SHA-1 and presents a new digital signature technique, the Digital
Signature Algorithm (DSA)
• Originally proposed in 1991 and revised in 1993 and again in 1996
• Uses an algorithm that is designed to provide only the digital signature function
• Unlike RSA, it cannot be used for encryption or key exchange
Encryption and the Internet
SSL (Secure Socket Layer)
• Transport layer security service
• Aubsequently became Internet standard known as TLS (Transport Layer Security)
• uses TCP to provide a reliable end-to-end service
Uses Public Key Scheme
• Each client-server pair uses
o 2 public keys
▪ one for client (browser)
created when browser is installed on client machine
▪ one for server (http server)
created when server is installed on server hardware
o 2 private keys
▪ one for client browser
▪ one for server (http server)
Certificates – The Web Browser Perspective
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