Lecture 12 - Cryptography

Plaintext

a message in its original form

Ciphertext

a message in the transformed, unrecognized form

Encryption

the process that transforms a plaintext into a ciphertext

Decryption

the process that transforms a ciphertext to the corresponding plaintext

Key

the value used to control encryption/decryption

Symmetric encryption

the key used to encrypt a message is the same as the one used to decrypt it

Asymmetric encryption

the key used to decrypt a message is different from the key used to encrypt it

Algorithm and Key

Algorithm performs encryption or decryption; key is essential for determining cipher output.

brute force attack

try all possible keys on some ciphertext until get an intelligible translation into plaintext (used if don't know the key)

Key management

With symmetric encryption, the communicating parties must share the one key.

Keys must be shared among the senders and receivers very carefully.

Separate key used for communications for different companies

Data Encryption Standard (DES)

Developed in the mid-1970s. The most common form uses a 56-bit key, which can be broken by experts in less than a day.

Triple DES (3DES)

Three different keys to produce the encrypted text.

Advanced Encryption Standard (AES)

Using the most advanced computers and techniques available today, it will require about 150 trillion years to crack AES by brute force.

Life span is around 20 years

RSA

most popular form of asymmetric encryption, 2 keys, 1 public for encryption, and 1 private for decryption.