Symmetric Stream Cipher Flashcards
RC4
Most widely used software stream cipher. Used identically for encryption and decryption.
To generate the key stream, the cipher makes use of a secret internal statewhich consists of two parts: A permutation of all 256 possible bytes (s) Two 8-bit index-pointers (i and j)
The permutation is initialized with a variable length key, typically between 40 and 256 bits, using the key-scheduling algorithm (KSA)
Then the stream of bits is generated using the pseudo-random generation algorithm (PRGA)
FISH
The FISH (FIbonacci SHrinking) cipher is a software-based stream cipher using the Lagged Fibonacci generator along with a concept borrowed from the shrinking generator cipher
PIKE
An improvement to fish, by Ross Anderson.
Anderson showed that Fish was vulnerable to known plaintext attacks.
Hash Function
Is a function that takes a variable size input m and returns a fixed size string
h=H(m)
Other properties a good Hash function should have include: The input can be of any length The output has a fixed length H(x) is relatively easy to compute for any given x H(x) is one-way H(x) is collision-free
Hash - Salt
Salting the input data makes it more difficult for dictionary attacks. Adds random values along with the plaintext to make it more complex
MD5
128-bit has htat is specified by RFC 1321
A flaw was found in MD5 and cryptographers recommended using SHA-1 instead.
NOT collision-resistant
MD5 Algorithm
The input message is broken into 512 byte chunks (16-32 bit integers) The message is padded with zeros if needed to reach 512 byte chunks The length of the message (before padding) is then appended as the last 64 bits of the message The algorithm operates on a 128-bit state, divided into four 32-bit words, denoted A, B, C and D. They are initialized to an initial variable The algorithm consists of 4 stages or rounds, each of which consists of 16 similar operations Those operations are a non-linear function F, a modular operation, and a shift
MD6
uses a merkle tree-like structure to allow for immense parallel computation of hashes for very long inputs.
SHA
The Secure Hash Algorithm is perhaps the most widely used hash algorithm today. There are now several versions of SHA. SHA (all versions) is considered secure and collision free.
SHA-1
A 160-bit has function that resembles the earlier MD5 algorithm, Designed by the NSA to be part of the Digital Signature Algorithim.
SHA-2
Actually, two similar has functions with different block size known as SHA-256 and SHA-512
FORK-256
This hash function uses 512-bit blocks and implements preset constants that change after each repetition. Each block is hashed into a 256-bit block through four branches that divides each 512 block into sixteen 32-bit words that are further encrypted and rearranged. Because the four branches are used in parallel, whereas SHA-256 uses four serial rounds, FORK-256 is hard to analyze. It is still in analysis phase and not in widespread use.
RIPEMD-160
RACE Integrity Primitives Evaluation Message Digest (RIPEMD-160) is a 160-bit hash algorithm developed by Hans Dobbertin, Antoon Bosselaers, and Bart Preneel. There exist 128-, 256-, and 320-bit versions of this algorithm, called RIPEMD-128, RIPEMD-256, and RIPEMD-320, respectively. These all replace the original RIPEMD which was found to have collision issues. The larger bit sizes make this far more secure that MD5 or RIPEMD.
GOST
Produces a fixed length output of 256 bits. the input message is broken up into 256 bit blocks and padded if it is less than that. Then it it hashed and the sum of the hashes is added up and add into the algorithm for the final output.
TIGER
outputs a 192 bit hash value and was developed by Ross Anderson and Eli Biham.
