Diff for "Csce877Ch11Notes"

Authenicator

Additional information appended to a message to enable the receiver to verify that the message should be accepted as authentic. The authenticator may be functionally independent of the content of the message itself (e.g., a nounce or a source identifier) or it may be a function of the message contents (e.g., a hash value or a cryptographic checksum).

Birthday Attack

When short hash codes are used it is not difficult to find two messages that produce the same hash code, but have slightly different meanings - p332-333.

Birthday Paradox

Let latex2($P(n,k)$) be the probability that at least one duplicate in k items exists when each item can take on one of n different values. So latex2($P(365,10)$) is the probability that we have a duplicate in 10 peoples birthdays. It is easier to calculate the number of ways we can not have a duplicate latex2($N=365 \times 364 \times ... \times (365-k+1) = \frac{365!}{(365-k)!}$). The number of ways with duplicates is latex2($N_D = (365)^k$). Then the probability of at least one duplicate is latex2($1-\frac{365!}{(365-k)!(365)^k}$)

Compression Function

In the context of hash functions takes two inputs: (1) an n-bit input from the previous step called a chaining variable and a b-bit block (block of the message), and outputs a n-bit output.

Cryptographic Checksum

An authenticator that is a cryptographic function of both the data to be auth4enticated and a secret key. Also referred to as a message authentication code (MAC)

Hash Function

A function that maps a variable-length data block or message into a fixed-length value called a hash code (also referred to as a message digest).