Encryption Fundamentals

Encryption transforms plaintext into ciphertext using a key. Plaintext (p) is the original message, ciphertext (c) is the encrypted message, and the key (k) is used for both encryption and decryption.

The process of transforming ciphertext back into plaintext using the key, also known as unlocking the message.

The original message before encryption

The encrypted message that only the intended recipient can understand.

A secret piece of information that is used to encrypt and decrypt messages.

The process of using the same key for both encryption and decryption.

An attacker who tries to intercept or decrypt messages.

Alice wants to send a message to Bob securely. She uses encryption to ensure that only Bob can understand the message.

The principle that the security of a cryptosystem should not rely on keeping the algorithm secret, but rather on keeping the key secret.

The practice of relying on secrecy of implementation as a security measure. This is generally considered a bad security practice.

The practice of relying on secrecy of implementation as a security measure. This is generally considered a bad security practice.

Security through obscurity is a bad practice because it relies on the secrecy of the implementation, which can be compromised. A better approach is to rely on strong cryptography that is openly analyzed and scrutinized by the community.

In cryptographic systems, it is generally discouraged to create your own encryption algorithms. This is because it is very easy to make mistakes in cryptography, and it's very hard to find those mistakes.

A Pseudo Random Generator (PRG) generates a sequence of bits that appear random but are actually determined by a seed value. They are useful for generating keys and other cryptographic material.

A PRG in Linux systems is accessible through the /dev/urandom file. The file is mapped to the PRG allowing access from any process.

Statistical tests analyze sequences of bits to see if they meet certain statistical properties, like balanced distribution of 0s and 1s. These tests are not enough to guarantee security.

Even if a sequence of bits passes statistical tests, it can still be insecure for cryptographic purposes. An attacker can use specific patterns or weaknesses in the PRG to predict future bits.

Always double-check system calls that access the /dev/urandom file. Make sure they are successful to avoid introducing vulnerabilities in your program.

A function that generates a strong encryption key from a less secure input like a password.

A type of secure hardware used to store and generate cryptographic keys. It is designed to protect sensitive data from unauthorized access, even if the host system is compromised.

A process that involves encrypting a long-term encryption key using another key, often referred to as a wrapping key.

Keys are often the most crucial elements in a secure system, as they are used to protect sensitive information.

A method of encrypting data using a unique key that is specifically generated for the user. It is typically used for storing data securely on a device.

A secure storage mechanism where master keys are protected within tamper-resistant hardware, increasing the overall security of the system.

A cryptographic token that is small and portable, often used for storing authentication credentials and digital signatures.

A type of secure crypto-token that is designed to store and protect cryptographic keys, used for digital signatures, identity verification, and other security tasks.

A measure of the difficulty of breaking a cryptographic system.

The computational effort required for the most efficient attack to succeed.

The minimum number of steps needed to break a cryptographic system using the best known attack.

A method of trying every possible key until the correct one is found.

A key with n-bits cannot provide more than n-bit security because the best possible attack would only need to try 2^n possible keys.

The number of attempts an attacker needs to make to break the encryption.

The most direct way to break a cryptosystem. Involves trying all possible keys until the correct one is found.

The number of bits in a key determines its security. An n-bit key means there are 2^n possible combinations.

A type of cipher that encrypts data in blocks of a fixed size, using a key. For example, let's say we encrypt a block of 128 bits, known as a plaintext block, using a key. The encryption algorithm then transforms this block into a ciphertext block of the same size. To decrypt the ciphertext, we essentially reverse the process using the same key.

A block cipher's decryption algorithm uses the same key as the encryption algorithm to transform ciphertext back into plaintext. This ensures that only someone with the key can decode the encrypted message.

A block cipher is considered 'invertible' because using the key, you can always recover the original plaintext from the ciphertext. This means it's a one-to-one mapping between plaintext and ciphertext.

AES is a widely used block cipher with various key lengths, including 128, 192, and 256 bits. It encrypts data in 128-bit blocks, like fitting 128 marbles in a secure box. Its strength is also in its key size. A longer key, like 256 bits, makes it much harder for someone to guess the key and thus decipher the message.

AES was chosen after a public competition hosted by NIST from 1997 to 2000. The goal was to find a secure and efficient encryption algorithm. This process set a standard for choosing secure encryption methods.

AES is used in various hardware and software applications. Its widespread adoption is due to its speed and security. For example, it's likely used in your computer and mobile phone.

AES uses a state of 128 bits, organized as a 4x4 array, like a grid of 16 squares. It transforms this state through different rounds using a combination of permutations (like rearranging the bits) and substitutions (like replacing bits with different values).

AES uses a 'substitution-permutation network'. These are like a series of operations applied to your state (data). The operations mix the data heavily, making it difficult to reverse the process without knowing the key.

SubBytes in AES involves replacing each byte (8 bits) in the state array with another value based on a predefined S-Box. It's essentially a look-up table where each combination of 8 bits is assigned a unique different 8 bits.

ShiftRows in AES involves shifting each row of the state array to the left by a specific number of positions. It's like a cyclic shift, where the bits at the beginning of the row are moved to the end.

MixColumns in AES involves mixing the bits within the state array using a mathematical operation that involves multiplication and addition. It's like scrambling the bits within each column.

The number of rounds in AES depends on the key size: 10 rounds for a 128-bit key, 12 rounds for a 192-bit key, and 14 rounds for a 256-bit key. Each round consists of the steps: SubBytes, ShiftRows, MixColumns (except for the last round), and AddRoundKey.

AddRoundKey combines the state array with a round key derived from the original key. It involves a simple XOR operation, similar to flipping a switch on or off. This mixes the key with the data at each round.

In AES, the round keys are generated from the initial key using a key schedule algorithm, which takes the original key and expands it to generate a series of round keys, one for each round in the encryption process.

Directly using a block cipher to encrypt messages can leave you vulnerable to various security risks. It involves issues like not being able to encrypt messages longer than the block size and the potential for repeating patterns in the ciphertext. These issues can lead to attacks.