Symmetric Encryption

Blowfish and Twofish

Blowfish performs a 64-bit block cipher at very fast speeds. It's a symetric block cipher that can have variable key lengths from 32 bits to 228 bits. Twofish is quite similar and works on 128-bit blocks. The distinctive of Twofish is that it has a complex key schedule.

Data Encryption Standard (DES)

Based on a 56-bit key and has several other modes that offer security and integrity. DES actually generates a 64-bit key, but 8 of those bits are just for error correction and only 56 bits are the actual key. ◇ Triple-DES is regular DES with a 168-bit key.

Ron's Cipher (RC)

Current levels are RC4, RC5, RC6. Is popular with wireless and WEP/WPA encryption. It is a streaming cipher that works with key sizes between 40 and 2048 bits and is used with SSL and TLS.

International Data Encryption Algorithm (IDEA)

Its an algorithm that uses a 128-bit key. Similar to the speed and capability to DES but is more secure. This is used in Pretty Good Privacy (PGP).

One-time Pads

Only truly completely secure cryptographic implementations. This is true for two reasons, One, it uses a key that is as long as a plaintext message which means there is no pattern in the key application for an attacker to use. One-time Pad keys are only used once and then discarded. ◇ Vernam's cipher is an example. He proposed a stream cipher that would be used with teleprinters. It combines a prepared key, character by character, which is stored on a paper tape, with the characters of the plain text to produce the cipher text. The recipient would again apply the key to get back the plain

Advanced Encryption Standard (AES):

Replaced DES and uses the Rijndael algorithm. It supports key sizes of 128,192, and 256 bits.

Galois Counter Mode (GCM)

This mode uses a hash function of a binary Galois field to provide encryption that is authenticated. GCM uses a Galois field with a hash to have an authenticated cipher.

Electronic Code Book (ECB)

To use the algorithm without any modification at all. You implement the algorithm exactly as it was designed.

CAST

Used in some products offered by Microsoft and IBM. It uses a 40-bit to 128-bit keys and is fast and efficient. ◇ CAST-128 and CAST-256 also exist.

Counter mode (CTM or CTR)

Used to convert a block cipher into a stream cipher. It basically works by generating keystream block by encrypting sequential values of some counter. This counter can be any function that produces a sequence that has a long period with no repetition.

GOST

Uses a 64-bit block and a key of 256 bits. It is a 32-round Feistel Cipher. Official Designation is GOST 2814789.

Cipher-block chaining(CBC)

What this mode does is when one block is finished encrypting, before the second block is started, the output of the first block is XOR'd with plain text of the next block. This causes more diffusion and makes known plain-text attacks totally ineffective.

Symmetric Cipher Issues

• Latency: they need to have low latency to be able to be processed quickly. This is important for low power devices to reduce the amount of power that is consumed. • High resiliency: Concern is various rather than advanced attacks that can "leak" a portion of the secret key, such as with side-channel attacks.