Introduction to Cryptography

What is Cryptography?

• The practice and study of techniques for secure communication in the presence of third-party adversaries
• encrypting plaintext (readable data) into ciphertext (unreadable data) to protect it from unauthorized access

Types of Cryptography

• Symmetric-key cryptography: uses the same secret key for both encryption and decryption
  • Examples: AES (Advanced Encryption Standard), DES (Data Encryption Standard)
• Asymmetric-key cryptography: uses a pair of keys: a public key for encryption and a private key for decryption
  • Examples: RSA (Rivest-Shamir-Adleman), elliptic curve cryptography

Cryptographic Algorithms

• Block ciphers: encrypt data in fixed-length blocks
  • Examples: AES, DES
• Stream ciphers: encrypt data one bit or byte at a time
  • Examples: RC4, FISH
• Hash functions: one-way encryption, cannot be decrypted
  • Examples: SHA-256, MD5
• Digital signatures: use asymmetric cryptography to authenticate and ensure integrity of messages
  • Examples: RSA, ECDSA (Elliptic Curve Digital Signature Algorithm)

Cryptographic Techniques

• Confidentiality: protecting data from unauthorized access
• Authentication: verifying the identity of the sender or recipient
• Integrity: ensuring data is not tampered with or altered
• Non-repudiation: ensuring a sender cannot deny sending a message

Cryptographic Attacks

• Ciphertext-only attack: accessing only the encrypted data
• Known-plaintext attack: accessing both the encrypted and decrypted data
• Chosen-plaintext attack: choosing the data to be encrypted
• Side-channel attack: attacking the implementation or environment of the cryptosystem rather than the algorithm itself

Cryptography Applications

• Secure online transactions (e.g., HTTPS)
• Secure communication protocols (e.g., SSL/TLS, IPsec)
• Digital currencies (e.g., Bitcoin)
• Secure email (e.g., PGP, S/MIME)
• Digital rights management (DRM)

What is Cryptography?

• Cryptography is the practice and study of techniques for secure communication in the presence of third-party adversaries.
• It involves encrypting plaintext (readable data) into ciphertext (unreadable data) to protect it from unauthorized access.

Types of Cryptography

Symmetric-key Cryptography

• Uses the same secret key for both encryption and decryption.
• Examples include AES (Advanced Encryption Standard) and DES (Data Encryption Standard).

Asymmetric-key Cryptography

• Uses a pair of keys: a public key for encryption and a private key for decryption.
• Examples include RSA (Rivest-Shamir-Adleman) and elliptic curve cryptography.

Cryptographic Algorithms

Block Ciphers

• Encrypt data in fixed-length blocks.
• Examples include AES and DES.

Stream Ciphers

• Encrypt data one bit or byte at a time.
• Examples include RC4 and FISH.

Hash Functions

• One-way encryption, cannot be decrypted.
• Examples include SHA-256 and MD5.

Digital Signatures

• Use asymmetric cryptography to authenticate and ensure integrity of messages.
• Examples include RSA and ECDSA (Elliptic Curve Digital Signature Algorithm).

Cryptographic Techniques

Confidentiality

• Protecting data from unauthorized access.

Authentication

• Verifying the identity of the sender or recipient.

Integrity

• Ensuring data is not tampered with or altered.

Non-repudiation

• Ensuring a sender cannot deny sending a message.

Cryptographic Attacks

Ciphertext-only Attack

• Accessing only the encrypted data.

Known-plaintext Attack

• Accessing both the encrypted and decrypted data.

Chosen-plaintext Attack

• Choosing the data to be encrypted.

Side-channel Attack

• Attacking the implementation or environment of the cryptosystem rather than the algorithm itself.

Cryptography Applications

• Secure online transactions (e.g., HTTPS).
• Secure communication protocols (e.g., SSL/TLS, IPsec).
• Digital currencies (e.g., Bitcoin).
• Secure email (e.g., PGP, S/MIME).
• Digital rights management (DRM).

Definition and Purpose

• Secure communication technique to protect against third-party adversaries
• Goals: confidentiality, integrity, and authenticity of messages

Basic Concepts

• Plaintext: original message or data to be protected
• Ciphertext: encrypted message or data, unreadable without decryption key
• Encryption: converting plaintext to ciphertext
• Decryption: converting ciphertext back to plaintext
• Key: piece of information for encryption and decryption

Types of Cryptography

• Symmetric-key cryptography: same key for encryption and decryption
  • Examples: AES, DES
• Asymmetric-key cryptography: pair of keys (public for encryption, private for decryption)
  • Examples: RSA, elliptic curve cryptography

Cryptographic Techniques

• Block ciphers: divide plaintext into fixed-length blocks, encrypt each block
  • Examples: AES, DES
• Stream ciphers: encrypt plaintext one bit or byte at a time
  • Examples: RC4, FISH
• Hash functions: one-way encryption, produces fixed-length string (digest) from variable-length message
  • Examples: SHA-256, MD5
• Digital signatures: asymmetric-key cryptography for sender authentication and message integrity

Cryptographic Attacks

• Brute force attack: try all possible keys to decrypt ciphertext
• Frequency analysis: analyze character frequency in ciphertext to deduce plaintext
• Side-channel attack: exploit implementation information, not the encryption algorithm itself
• Man-in-the-middle attack: intercept and alter communication between two parties

Cryptographic Protocols

• SSL/TLS: secure web browsing
• IPSec: secure network communication
• PGP: secure email communication
• SSH: secure remote access to computers