Question

What are some of the secure methods to generate a pseudorandom number sequence? (assume any secret key is kept private) Using the OFB mode of encryption to generate a number sequence (which can be used to XOR with the plaintext sequence).

a. Using repeated hashing with a random initial IV (assume a cryptographically secure hash function)
b. Use a linear congruential generator to output a sequence of pseudo-randomized numbers
c. By encrypting a constant value iteratively using AES.
d. By encrypting a random initialization vector iteratively using AES.
e. Using AES to encrypt a counter that increases 1 every time (but never repeats).

Answer 1

To generate a pseudorandom number sequence securely, one can use OFB mode of encryption, repeated hashing with a random IV, a linear congruential generator, AES encryption of a constant, AES with a random IV, or encrypting a non-repeating counter with AES.

Step-by-step explanation:

Some of the secure methods to generate a pseudorandom number sequence include:

• OFB mode of encryption: This method leverages the Output Feedback mode of an encryption algorithm, where a number sequence generated can be XORed with plaintext to provide security.
• Repeated hashing with a random initial IV: Assuming a cryptographically secure hash function, this technique applies hashing repeatedly to generate a pseudorandom sequence.
• Linear congruential generator: Although not the most secure, it provides a method for generating a sequence of numbers that are pseudo-randomized.
• Encrypting a constant value iteratively using AES: By applying AES encryption repeatedly on constant values, a sequence of numbers is produced.
• Encrypting a random IV iteratively using AES: Similar to the previous method, but uses a random initialization vector.
• Using AES to encrypt a counter: The counter is incremented by 1 each time, ensuring the sequence doesn't repeat, offering another level of security.

When utilized correctly, each of these methods can yield a secure sequence to aid in encryption and maintaining privacy.