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Cryptography

The process of communicating secretly through the use of cipher

Cryptanalysis

The process of cracking or deciphering; code breaking

Cryptology

The study of cryptography or cryptanalysis

Cleartext / plaintext

What you are reading now

Encrypt

convert information or data into code to prevent unauthorized access

Decrypt

convert an encoded or unclear message into something intelligible, to plaintext

Cipher

An algorithm to perform encryption and/or decryption

Cryptosystem

Suite of algorithms to perform encryption and/or decryption

VLC

best open source media player

Symmetric key

one key for encryption and decryption

applications

Pros:

Really easy to understand

Modified key K will result in garbage plaintext in decryption

Fast!

Cons:

Lose the key you’re screwed

How do you share the key

Brute forcing

Who knows who actually used the key

Those who know K can participate in communications (eavesdropping)

Impersonation attack if attacker knows K

Not good for authenticity

Asymetric Key

• Public Key Encryption

  • Two keys; one public, one private

  • Bob encrypts message with Alice's public key Alice decrypts the message with her private key

  • Pros:

    • Key sharing / distribution problem solved

    • Identity problem goes away

    • Public key can be distributed any way possible

    • Confidentiality: only holder of private key can decrypt message

    • Integrity: any modification of the message would be revealed when decrypting

    • Non repudiation: Bob can prove to a third party that Alice is the originator of the messa

  • Cons:

    • Computationally more expensive

    • Can still lose the private key

    • No authentication: anyone can encrypt a message given a public key

    • Man-in-the-Middle (MitM) attack

The golden rule

• dont create your own ciphers

Base64

encoding scheme

The only unbreakable encryption

OTP (one time pad) - mixes a secret message with a random key of the same length