Cryptography

Objectives

Understanding Cryptography Concepts, Overview of Encryption Algorithms, Cryptography, Cryptography Tools, Understanding Public key Infrastructure, Understanding Email Encryption, Understanding disk encryption, Understanding cryptographic attacks, cryptanalysis

Cryptography Concepts

• The conversion of data into a scrambled code that is decrypted and sent over a private or public network
  • Used for email messages, chat sessions, web transactions, personal data, corporate data, e-commerce apps, etc.
• Types of Cryptography
  • Symmetric Encryption: Uses the same key for encryption as it does for decryption
  • Asymmetric Encryption: Uses different key for encryption for encryption and decryption
• Government Access to Keys (GAK)
  • Software companies will give copies of all keys
  • Government promises they will hold on to the keys in a secure will, and will only use them when a court issues a warrant to do so
    • Gives them ability to wiretap phones

Encryption Algorithms

• Cipher is an algorithm for performing encryption and decryption
  • Classical Cipher: Most basic type, operates on the alphabet (A-Z)
  • Modern Ciphers: provide secrecy, integrity, and authentication of sender. Uses a one-way mathematical function capable of factoring large prime numbers *Block Ciphers: Deterministic algorithm operating on block of fixed size with an unvary transofmration specified by a symmetric key.
    • Stream Ciphers: Symmetric key ciphers are plaintext digits combined with a key stream (random).
  • Data Encryption Standard (DES)
    • Uses a secret key for both encryption and decryption (symmetric). 62 bit secret key.
  • Advanced Encryption Standard (AES): Symmetric key algorithm for securing sensitive but unclassified material by U.S. Government agencies (128 bit)
  • RC4 variable key size stream cipher
  • RC5: parameterized algorithm with variable block size, 128 bits
  • RC6: Symmetric key block cipher derived from RC5
  • Digital Signature Algorithm(DSA): Specifies algorithm to be used in the generation and verification of digital signatures for sensitive, unclassified application
  • Digital Signature: Computed using a set of rules (I.e, the DSA) and a set of parameters
  • RSA (Rivest Shamir Adleman)
    • RSA is an internet encryption and authentication system
    • Widely used and is one of the de facto encryption standard
    • Uses modular arithmetic and elementary number theories
  • Message Digest (one way Hash)
    • Hash functions calculate a unique fixed-size bit string
    • Every output bit has a 50% of changing
    • MD5, SHA 128/256
• Secure Hashing Algorithms
  • SHA-1: Produces 160 digest with maximum length 264-1, resembles MD5
  • SHA-2: comprised of SHA-256 and SHA-512(64 bit)
  • SHA-3: Uses sponge construction in which message block are XORed
• What is SSH (Secure Shell)
  • Replacement for telnet
  • Provides an encrypted channel
  • Provides strong host-to-host and user authentication

Public Key Infrastructure

• Public Key infrastructure (PKI): set of hardware, software, people, policies, and procedures required to create, manage, distribute, use , store, and revoke digital certificates
• Signed CA vs Self Signed: Signed is more trustworthy

Email Encryption

• Digital signature used asymmetric cryptography to simulate the security properties of a signature in digital, rather than written form
  • A digital signature may be further protection, by encrypting the signed email
• SSL (Secure Sockets Layer): SSL is an app protocol developed for netscape for managing the security of a message transmission on the internet
  • It uses RSA asymmetric (public key) encryption
• Transport Layer Security (TLS): Protocol to establish a secure connection between a client and a sever. Uses RSA algorithm with 1024 and 2048 bit strengths

Cryptographic Attacks

• Ciphertext only attack: goal of this attack to recover encryption key from cipher text
• Adaptive Chosen-plaintext attack: attacker makes a series of interactive queries
• Chosen-plaintext attack: attacker defines his own plaintext, feeds it into the cipher, and analyzes the resulting cipher text
• Chosen-plaintext Attack: Attacker defines his own plaintext, feeds it into the cipher, and analyzes the resulting ciphertext
• Known-plaintext Attack: Attacker has knowledge of some part of the plain text
• Code Breaking Methodologies:
  • Trickery and Deceit: Social Engineering techniques
  • Brute Force: trying every possible combination
  • One-Time pad: contains many non-repeating groups of letters or number keys which are randomly chosen
  • Frequency Analysis: Study the frequency of letters or groups of letters in a ciphertext
• MITM on digital sig schemes
  • Attack works by encrypting one end and decrypting from the other end, the meeting in the middle
    • Can be used for forging signatures even on digital signatures
• Side Channel Attack: Physical attack performed on a cryptographic device/cryptosystem to gain sensitive informations