the process of analyzing available information in an attempt to return the encrypted message to its original form
comparing the input plaintext to teh output cipher text to try to determine the key
comparing plaintext to cipher text, but puts the plaintext through a simplified cipher to try and deduce what the key is likely to be in teh full version of the cipher
Step by Step, recursive computational procedure for solving a problem in a finite # of steps
The best algorithms are public and peer reviewed
special piece of data used in both teh encryption and decryption processes.
the algorithms stay the same in every implementation, but a different key is used for each.
substitute a different random letter for every letter
-due to the ease of breaking shift ciphers
Vigennere cipher or Polyalphabetic substitution cipher
links the cipher with a password. if the password is not long enough, the password is repeated until one character of the password is matched up with each character of the plaintext. Then apply to a grid where the plaintext is row and the password is column
e.g. SAMPLEMESSAGE and PASSWORDPASSW, HAEHHSDHHSSYA
The size of every possible key-value. When an algorithm lists a certain number of bits as a key it is defining the keyspace.
DES - Data Encryption Standard
uses a 56-bit key, allowing 72 x 10^15 possible values.
-broken by modern computers
1976 adopted as federal standard
uses a 128bit key or 340 x10^36 possible values.
128 bits is generally accepted as the minimum required to protect sensitive information
Recertified in 1983 and 1993.
segments the input data into blocks of a specified size, typically padding the last block to make it a multiple of the block size required
anything having to do with the exchange, storage, safeguarding, and revocation of keys.
most commonly associated with asymetric encryption or use of public and private keys.
one time pad ciphers
The keys are equal to the of the messages they protect and completely random must be used for the keys.
this allows for an unlimited keyspace and therefore brute force attack is practically impossible.
A logical function to perform encipherment. Uses binary.
e.g. 11011100 XOR 11111110(or 254) is 00100010.
compare the individual digits, if the same then the encrypted data is a 0, if different then 1
a special mathematical functio nthat performs one-way encryption.
i.e. once the algorithm is processed there is no feasible way to use the ciphertext to retrieve the plaintext that was used to generate it.
also ideally there is no way to ggenerate two different plaintexts that compute to the same hash value.
wherein an attacker finds two different messages that hash to the same value.
SHA - Secure Hashing Algorithm
MD2, 4, or 5: Message Digest 2, 4, or 5
Secure Hash Algorithm
uses a MD @ a particular bit length.
Included in the Federal Information Processing Standars 180-2, or FIPS 180-2
Consists of SHA -1, 256, 384, 512.
Latter variants are occasionally referred to as SHA-2
Developed in 1993
MD @ 160 bit
Modeled on the MD4 Algorithm
Input less than 2^64
32bit string converted to hex and formed into 16 words
-words make a 512 bit block. padded if not enough to make 512
Similar to SHA-1
2^64 bit input or less
256 bit hash
uses 64 32 bit words, 8 working variables
more secure than SHA-1, but the attac basis for SHA-1 can produce collisions in SHA-256
2128 bits of input
pads that to 1024 blocks
6 x64bit words to produce 284bit hash
same as 384
uses 8 64 bit words for final hash of 512
generric verrsion of one of several algorithms designed to create a hash or message digest(MD)
Ronald L Rivest of MIT
takes a data input of any length and produces a hash output of 128 bits.
optimized for 8 bit machines
inputs padded to be multiples of 16 bytes, then checksum is appended to the message
only known successful attack requires the checksum not be appended before the hash is run
some collision attacks are based on the algorithm's Initialization Vector(IV)
optimized for 32 bit computers
fast algorithm but subject to more attacks than MD5
padded to 512 bits, which is then concatenated with representation of message's orginal length
Then divided into 16 words of 32 bits.
Hans Dobbertin has shown how collisions can be found in under a minute using only a PC
most people are moving away from this to MD5 or SHA
creates a 128bit hash of a message of any length
original message is padded to be 64 bits short of a multiple off 512 bits, then a 64 bit representation
both sender and receiver have previously obtained a copy of the same key