Look at the following two pieces of text:

The text on the left side is a secret message. The message has been encrypted, or turned into a secret code. It will be completely unreadable to anyone who doesn’t know how to decrypt it (that is, turn it back into the plain English message.) This book will teach you how to encrypt and
decrypt messages.

The message on the right is just random gibberish with no hidden meaning whatsoever. Encrypting your written messages is one way to keep them secret from other people, even if they get their hands on the encrypted message itself. It will look exactly like random nonsense. Cryptography is the science of using secret codes. A cryptographer is someone who uses and studies secret codes. This book will teach you what you need to know to become a cryptographer.

Of course, these secret messages don’t always stay secret. A cryptanalyst is someone who can hack secret codes and read other people’s encrypted messages. Cryptanalysts are also called code breakers or hackers. This book will also teach you what you need to know to become a cryptanalyst. Unfortunately the type of hacking you learn in this book isn’t dangerous enough to get you in trouble with the law. (I mean, fortunately.)

Spies, soldiers, hackers, pirates, royalty, merchants, tyrants, political activists, Internet shoppers, and anyone who has ever needed to share secrets with trusted friends have relied on cryptography to make sure their secrets stay secret.

Source

Cryptography is the practice and study of techniques for securing communication and information by transforming it into a format that is unreadable to unauthorized users. It involves creating codes and ciphers to protect data from eavesdropping, tampering, or forgery.

Here are some key aspects:

1. Confidentiality: Ensures that information is only accessible to those who are authorized to see it. This is often achieved through encryption, which transforms readable data (plaintext) into an unreadable format (ciphertext).
2. Integrity: Ensures that the information has not been altered in transit. Hash functions are often used to verify the integrity of data.
3. Authentication: Confirms the identity of the parties involved in communication. This can be done through digital signatures and certificates.
4. Non-repudiation: Ensures that a sender cannot deny sending a message, providing proof of the origin and integrity of the data.

Types of Cryptography:

• Symmetric Key Cryptography: Uses the same key for both encryption and decryption.
• Asymmetric Key Cryptography: Uses a pair of keys (public and private) for encryption and decryption, enhancing security.

Applications: Cryptography is used in various applications, including secure communications (like SSL/TLS for websites), digital currencies (like Bitcoin), secure email, and many forms of data protection.

Overall, cryptography is essential for protecting sensitive information in our increasingly digital world.