Exam 7: Random and Pseudorandom Number

The longer the keyword the more difficult the cryptanalysis.

A cryptographically secure pseudorandom bit generator is defined as one that passes the least significant bit test.

The principle requirement of random or pseudorandom number generation is that the generated number stream be unpredictable.

With true random sequences each number is statistically independent of other numbers in the sequence and therefore unpredictable.

A __________ is used to produce a pseudorandom string of bits of some fixed length.

In key distribution and reciprocal authentication schemes two communicating parties cooperate by exchanging messages to distribute keys and/or authenticate each other.In many cases ___________ are used for handshaking to prevent replay attacks.

Two approaches that use a block cipher to build a PNRG and have gained widespread acceptance are:

If the PRF does not generate effectively random 128-bit output values it may be possible for an adversary to narrow the possibilities and successfully use a brute force attack.

Two distinct requirements for a sequence of random numbers are unpredictability and __________ .

An algorithm that is used to produce an open-ended sequence of bits is referred to as a ___________ .

Three broad categories of cryptographic algorithms are commonly used to create PRNGs: symmetric block ciphers,asymmetric ciphers,and hash functions and message authentication codes.

Various methods of modifying a bit stream to reduce or eliminate a bias have been developed.These are referred to as ___________ algorithms.

In a stream cipher structure a key is input to a pseudorandom bit generator that produces a stream of 8-bit numbers that are apparently random.The output of the generator,called a ___________ ,is combined one byte at a time with the plaintext stream using the bitwise exclusive-OR operation.

The most important and widely used stream cipher is __________ .

There are well-defined tests for determining uniform distribution and independence to validate that a sequence of numbers is random.

Examples of a pseudorandom function are decryption keys and nonces.

The stream cipher is similar to the one-time pad with a difference being that a one-time pad uses a pseudorandom number stream and a stream cipher uses a genuine random number stream.

The distribution of bits in a random number sequence should be ___________ ,therefore the frequency of occurrence of ones and zeros should be approximately equal.

A stream of pseudorandom numbers should exhibit two forms of unpredictability: forward and __________ .

Two criteria used to validate that a sequence of numbers is random are uniform distribution and __________ .