Encryption Fundamentals

A method where the same secret “password” or key is used to both lock and unlock information. Imagine a single key for a locked diary — anyone with the key can open and close it. The challenge is making sure no one intercepts or copies the key while sending it.

Secret Key Encryption / Symmetric Cryptography

Exam Tips:

• Fast and efficient for encrypting large amounts of data.

• Weakness: Secure key distribution is required.

A method that allows two parties to securely agree on a secret key over an insecure channel, without anyone else being able to figure it out. Think of it like mixing two secret colors in public so only both parties end up with the same final color, but no eavesdropper can reproduce it.

Diffie-Hellman

Exam Tips:

• Primarily used to safely share symmetric keys.

• Relies on asymmetric math, but the output is a symmetric key.

Encrypts data in fixed-size chunks, like filling boxes with letters before locking them. If the last box isn’t full, padding is used to make it fit.

Block Encryption (Symmetric)

Exam Tips:

• Each block is processed individually.

• Slower than stream encryption for real-time data.

Encrypts data one bit or byte at a time, like a conveyor belt where each letter gets its own lock instantly. Perfect for real-time communications like voice or video.

Stream Encryption (Symmetric)

Exam Tips:

• Faster than block encryption.

• Bit errors can affect subsequent bits (error propagation).

Extra “filler” added to a block to make it fit the required size, like adding packing peanuts to a box so it’s full before sealing.

Padding (Zero, PKCS#7, ANSI X.923)

Exam Tips:

• Ensures last block fits block size for encryption.

• Must be removed during decryption.

A random value added at the start of encryption to make identical plaintexts encrypt differently, like adding a random “spice” to every dish so no two taste exactly the same.

A lookup table that replaces input bits with other bits in a nonlinear way to obscure the relationship between plaintext and ciphertext. Think of it like a secret decoder chart that scrambles letters unpredictably.

S-Box

Exam Tips:

• Adds confusion in block ciphers.

• Weak S-box design compromises entire cipher.

Adding random data to a message before encryption or hashing, like sprinkling a unique seasoning into each dish so repeated recipes taste different.

Salting

Exam Tips:

• Prevents identical plaintexts from producing identical ciphertexts.

• Often used with IVs and hashing.

A measure of how long or how many resources it takes to break an encryption, like the number of “lockpicks” or years needed to crack a safe.

Work Factor

Exam Tips:

• Higher work factor = stronger encryption.

• Must be reassessed as computing power increases.