University:
Boston University
Course:
GRS CS 910 | Directed Study: Systems
Academic year:

2020
Views:

26

Pages:

18
Author:

Ashley Bautista

INTRODUCTION to CRYPTOGRAPHY & CRYPTOGRAPHIC SERVICES on Z/OS History of Cryptography • The concept of securing messages through cryptography has a long history. • Julius Caesar is credited with creating one of the earliest cryptographic systems to send military messages to his generals. CAESAR’S SHIFT BY 3 RULE What Is Cryptography? As the field of cryptography has advanced, the dividing lines for what is and what is not cryptography have become blurred. Cryptography today might be summed up as the study of techniques and applications that depend on the existence of difficult problems. But the field of cryptography contains even more when we include some of the things cryptography enables us to do How is it Applied? Secure Communication Identification & Authentication CRYPTOGRAPHY Certification Key Recovery Remote Access How Does Cryptography Work? • A cryptographic algorithm, or cipher, is a mathematical function used in the encryption and decryption process. • A cryptographic algorithm works in combination with a key—a word, number, or phrase—to encrypt the plaintext. • The same plaintext encrypts to different cipher text with different keys. • The security of encrypted data is entirely dependent on two things: the strength of the cryptographic algorithm and the secrecy of the key. • A cryptographic algorithm, plus all possible keys and all the protocols that make it work, comprise a cryptosystem. Basic Elements of Cryptography • Encryption: converts data into some unreadable form • Decryption: transforms the encrypted data back into its original, intelligible form and serves as the reverse of encryption • Authentication: can be used to identify (individual user, a machine, an organization, etc) • Digital signatures: serves as the digital equivalent of paper signatures by binding a document to the holder of a particular key • Signature verification: verifies the validity of a particular signature Symmetric Key Encryption • In symmetric-key encryption, one key is used both for encryption and decryption. PRO Very efficient use of CPU for bulk data CON Key Management and Security Issues (Large number of business partners; keys decrypting data can exist in more than one place) Public-Key Cryptography • Removes the need to use the same key for encryption and decryption • Key Pairs are Used (Public/Private) – Public Key: Shared with Business Partner’s and used to encrypt data – Private Key: Kept by the key pair owner and used almost exclusively for decryption. This key is *never* shared • Not subject to same key management and security issues as symmetric keys • Matched “public” and “private” keys • Prior to the invention of public-key cryptography, it was very difficult to provide key management for large-scale networks Public-Key Encryption: Two Keys Common Public-Key Algorithms • RSA: for both digital signatures and key exchange. The Rivest-Shamir-Adleman (RSA) cryptographic algorithms are the most widely used public-key algorithms today, especially for data sent over the Internet. • DSA: for digital signatures only. The Digital Signature Algorithm (DSA), invented by the United States National Security Agency (NSA). • Diffie-Hellman: for key exchange only. DiffieHellman, the first public-key algorithm invented. Using Public-Key Encryption for Digital Signatures • Is a means for originators of a message, file, etc. to provide a signature for the information. • Frequently, digital signatures are used when data is distributed in cleartext Authentication (Who Is The Data From) • Signing Provides Non-Repudiation (User Cannot Deny the Data is Theirs) • Sender Encrypts Signature with Private Key • Receiver Decrypts Signature with Public Key Certificate • A public key certificate, often referred to simply as a certificate, is used for authentication and secure exchange of information on the Internet, extranets, and intranets. • A public key certificate is a digitally signed statement that binds the value of a public key to the identity of the subject (person, device, or service) that holds the corresponding private key. • Certificates can be issued for a variety of functions. Certification Authority • A certification authority (CA) is an entity trusted to issue certificates to an individual, a computer, or any other requesting entity. • A CA can be a remote third party • Three Types of CAs – Self-Signed CA – Subordinate CA – Root CA Example of a Certification Hierarchy Key Management • Key Management deals with the secure generation, distribution, and storage of keys. • Users must be able to securely obtain a key pair suited to their efficiency and security needs. • If the private key is lost or compromised, procedures to notify others must be in place to minimize the exposure. Key Size • • What size key do I need? What is the life cycle of a key? W. Ford, Computer Communications Security Principles, describes the cycle as: 1. 2. 3. 4. 5. 6. 7. Key generation and possibly registration (for a public key) Key distribution Key activation / deactivation Key replacement or key update Key revocation Key termination, involving destruction or possibly archival www.rsasecurity.com/rsalabs/ for current information on recommended key sizes Security Pitfalls Against Cryptographic Designs Against Implementations Against the Cryptography ATTACKS Against Passwords On the Users Against Trust Models Against Hardware

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