AES (Advanced Encryption Standard) A fast and secure method of symmetric encryption used worldwide. It is a block cipher, encrypting data in fixed-size blocks. Example: Used to encrypt files or data on a USB stick or to secure network traffic.

Asymmetric Encryption A type of cryptography based on algorithms that require two keys: a public key to encrypt data and a private key to decrypt it. Example: RSA is a common asymmetric encryption algorithm. It's ideal for securing data in transit (e.g., across the internet) and enables secure key exchange.

Authentication The process of verifying that you really are the person who has the right to access a particular computer or service. Example: When you log in to your email with a username and password, the system is authenticating your identity.

Caesar's Cipher A simple technique for encryption that shifts each letter of the alphabet by some fixed number of characters. Example: With a shift of 3, 'A' would become 'D', 'B' would become 'E', and so on.

Cipher The generic term for a technique or algorithm that performs encryption. Example: Caesar's Cipher, AES, and RSA are all types of ciphers.

Ciphertext The scrambled, unreadable version of a message after it’s been encrypted. This appears as random and incomprehensible gibberish. Example: An encrypted message like "H8d$#92!" before decryption.

Cracking The act of attempting to decode a secret message without knowing all the specifics of the cipher or the correct key. Example: Trying to guess a password or breaking an encryption by trying every possible key (brute-force attack).

Decryption The process that reverses encryption, taking ciphertext and reproducing the original plaintext, using the appropriate key. It makes the secret message readable again. Example: A recipient uses a key to turn "H8d$#92!" back into "My secret message."

Encryption The process of encoding messages to keep them secret, so only "authorized" parties can read them. In simplest terms, it means converting readable data into code. Example: Websites using HTTPS (indicated by a padlock icon) encrypt data transferred between your browser and the server to protect your information.

Frequency Analysis The study of how often letters or groups of letters occur in ciphertext. This technique can be used to break simpler substitution ciphers. Example: Noticing that 'E' is the most common letter in English plaintext and looking for the most common letter in the ciphertext as a potential 'E'.

Hashing A one-way process that transforms data of any size (like a password or a file) into a fixed-length code or "hash value." It cannot be reversed to reconstruct the original data. Example: SHA-256 is a common hashing algorithm used to verify data integrity or store passwords securely.

Key A secret value or piece of information (a string of bits) used by a cryptographic algorithm for both encryption and decryption. The more complex (longer) the key, the more secure the encryption. Example: Without the correct key, you cannot decrypt a message or access encrypted data.

Key Exchange Problem The challenge of securely distributing and agreeing on a shared secret key between two parties, especially in symmetric encryption, without the risk of it being intercepted by unauthorized parties. Example: If Alice and Bob want to use symmetric encryption, they first need a way to securely share the secret key without an eavesdropper stealing it.

One-way Function A process that is easy to compute on every input, but computationally infeasible (extremely difficult) to invert or reverse given only the output. Example: Hashing functions like SHA-256 are considered one-way functions.

Plaintext The original, readable message or information before it’s encrypted. Example: "My password is 12345" or an unencrypted email message.

Private Key In asymmetric encryption, this is the secret key that only the owner should possess. It is used to decrypt messages that were encrypted with the corresponding public key. Example: When you receive an email encrypted with your public key, you use your private key to open and read it.

Public Key In asymmetric encryption, this key is shared openly and can be accessed by anyone. It is used by others to encrypt messages intended for the owner of the key. Example: Anyone can use your public key to send you a secure message, knowing only you can decrypt it with your private key.

Random Substitution Cipher An encoding technique that maps each letter of the alphabet randomly to different letters or characters. Example: Instead of 'A' always being 'D' (like in Caesar's), 'A' might be 'X' in one message and 'Z' in another, based on a random mapping.

RSA (Rivest–Shamir–Adleman) A widely used asymmetric encryption algorithm that relies on the mathematical difficulty of factoring large prime numbers. Example: Used extensively in secure websites (HTTPS), digital signatures, and for secure email communication.

Salting The process of adding a unique, random string of data (a "salt") to a password before it is hashed. Example: If two users have the same password, salting ensures that their stored hashes will be different, making it much harder for attackers to use pre-computed tables to crack passwords.

SHA-256 (Secure Hash Algorithm 256-bit) A specific cryptographic hash function that produces a fixed-size 256-bit (32-byte) hash value. It is considered very secure for its purpose. Example: Often used to store passwords safely by hashing them, and to verify the integrity of files (e.g., to ensure a downloaded file hasn't been tampered with).

Symmetric Encryption A type of cryptography where the same cryptographic key is used for both encrypting plaintext and decrypting ciphertext. Also known as "private key encryption." Example: AES is a common symmetric encryption algorithm. It's ideal for encrypting data at rest (stored data) due to its speed.

Vigenere Cipher A method of encrypting text by applying a series of Caesar ciphers based on the letters of a keyword. It is more complex than a simple Caesar's Cipher. Example: If the keyword is "CAT" and the message starts "HELLO", the first letter 'H' might be shifted by 'C' (3 places), 'E' by 'A' (1 place), 'L' by 'T' (20 places), and so on, cycling through the keyword.