Introduction to Cryptography

Introduction

• While networking protocols have made it possible for devices spread across the globe to communicate, cryptography has made it possible to trust this communication.

Importance of Cryptography

• The ultimate purpose of cryptography is to ensure secure communication in the presence of adversaries.
• Cryptography is used to protect confidentiality, integrity and authenticity.
• Various compliances are in place to ensure secure communication.
  • For example, Credit cards should comply with Payment Card Industry Data Security Standard (PCI DSS).

Plaintext to Ciphertext

• Plain text - Original readable data.
• Ciphertext - Scrambled unreadable version of data after encryption.
• Cipher - Algorithm or method to convert plaintext to ciphertext and vice versa.
• Key - String of bits the cipher uses to encrypt or decrypt data.
• Encryption - Process of converting plain text to cipher text using a cipher through the key.
• Decryption - Process of converting cipher text back to plain text using a cipher through the key.

Historical Ciphers

• Cryptography’s history is long and dates back to ancient Egypt in 1900 BCE.
• One of the simplest historical ciphers is the Ceaser Cipher.
• In Ceaser Cipher every character in the plaintext is shifted to a certain number specified in the key.
• There are only 25 possible combinations in Ceaser cipher as the number of characters in English alphabets is 26.
• Online tools to encrypt and decrypt Ceaser cipher are
  • https://cryptii.com/pipes/caesar-cipher
  • https://www.dcode.fr/caesar-cipher

Types of Encryption

• There are two main categories of encryption
  • Symmetric Encryption
  • Asymmetric Encryption

Symmetric Encryption

• Uses the same key to encrypt and decrypt data.
• It is also called Symmetric Cryptography or Private Key Cryptography.
• Examples of Symmetric Encryption are
  • DES - Data Encryption Standard. Adopted in 1977.
  • 3DES - Triple DES. DES applied 3 times.
  • AES - Advanced Encryption Standard. Adopted in 2001.

Asymmetric Encryption

• Uses a pair of keys. One for encryption and the other for decryption.
• It is also called Asymmetric Cryptography or Public Key Cryptography.
• Examples of Asymmetric Encryption are
  • RSA - Supported key size 2048, 3072, 4096 bits.
  • Diffie-Hellman - Supported key size 2048, 3072, 4096 bits..
  • ECC - Elliptic Curve Cryptography. ECC can achieve equivalent security with shorter keys. For example: 256-bit ECC key is equivaluent to 3072 bit RSA key.

Basic Math

• Two common operations used in various algorithms
  • XOR operation
  • Modulo operation

XOR

• Also called exclusive OR.
• Returns 1 when the bits are different and 0 when they are same.
• For example:
  • 0 XOR 0 returns 0.
  • 1 XOR 1 returns 0.
  • 0 XOR 1 returns 1.
  • 1 XOR 0 returns 1.

Modulo

• Also called as % or mod.
• X % Y returns the remainder when X is divided by Y.
• The modulo operation always returns a non-negative result less than the divisor.