8. Cryptographic Algorithms & Security

Asymmetric Key Encryption

*1 -* Asymmetric Key Encryption is a form of encryption where the keys come in pairs. What one key can encrypt, only the other can decrypt. I.e. Asymmetric Key Encryption uses *different key for both encryption and decryption. *2 -* The pair of keys are very large numbers; one public and one private. *3 -* Anyone can encrypt using the public key but only the holder of the private key can decrypt the data. Decryption only possible if private key in known. *4 -* The key is created form factorizing very large numbers (over 150 decimal digits) making it very hard to be broken. *5 -* Also referred to as Public Key Encryption

Symmetric Key Encryption

*1 -* Symmetric key algorithms are algorithms that used the same cryptographic key for both encrypting of plain-text and decryption of cipher-text. I.e. Symmetric Key Encryption uses the *same key* for both encryption and decryption. *2 -* Keys may be identical or there may be a simple transformation to go between the two keys. *3 -* The keys, in practice, represent a shared secret between two or more parties that can be used to maintain private information link. *4 -* The requirement that both parties have the description key is one of the main drawback of Symmetric Key Encryption. *5 -* Also referred to as Private Key Encryption

Advanced Encryption Standards (AES)

- Invitation for proposal in 1997 - In progress - Key size 128, 192 and 256 bits

Rivest Shamire & Adelman (RSA)

- Relies on N = P * Q (product of two very large primes) - Factorization of N is hard - Choose key 'e', 'd' such that: ---- E x d = 1 mod Z where Z = (P - 1) x (Q - 1) - It can encrypt M by M^e mod N - It can decrypt by C^d mod N (C = encrypted message) - Therefore it can easily make e and N public while retaining d.

Asymmetric Encryption (Public Key) - Examples

- Rivest Shamire and Adelman (RSA) - Needham-Schroeder Public-Key

Symmetric Encryption - Examples

- Tiny Encryption Algorithm (TEA) - Data Encryption Standards (DES) - Advanced Encryption Standards (AES) - Needham-Schroeder Private-Key

Data Encryption Standards (DES)

- US standard for business applications until recently - 64 bit plaintext, 56 bit key - Cracked in 1997 - Triple DES (key 112 bits) still secure but poor performance.

Encryption

Encoding messages or information in such a way that only authorized parties can read it. The are two fundamental ways to use keys of secrets encryption: - Symmetric (Private Key) - Asymmetric (Public Key)

Security

Set a measure to guarantee the privacy, integrity and availability of resources: Objects, databases, processes, servers, channels, etc.

Tiny Encryption Algorithm (TEA)

Simple, concise yet secure and reasonably fast. - Key 128 bits (k[0]..k{3]) - Plaintext 64 bits (2 x 32 bits, text[0], text[1]...) - in 32 rounds combines plain text and key, swapping the two halves of plain text.