## 2 Background  
### Random Number  
Cryptographically secure random numbers are used in various security parameters. They must satisfy unpredictability, unbiasedness, and bit independence, and must provide security strength recommended in modern times. To ensure unbiasedness and bit independence, a deterministic random number generator (DRBG) is used; to satisfy unpredictability and security strength recommended by the government, various entropy sources (noise sources) are collected and mixed into the DRBG as input with recommended or higher security strength.  
In the field of cryptography (and statistics), randomness refers to the property of being selected randomly within a defined range, making it difficult to predict the outcome of an event or find patterns. Randomness is like the result of tossing a fair and unbiased coin continuously. If we assume that each side of the fair coin is represented by 0 or 1 when it is tossed once, the probability of getting either 0 or 1 is the same, and each toss is independent [5]. Therefore, the result of continuously flipping a fair coin is equivalent to the result of an ideal random number generator. A sequence is considered to be random if each bit is independent and identically distributed (IID) with equal probability [6].  
In an environment where encryption is used, random numbers must be unpredictable. Even a slight possibility of predicting random numbers can greatly affect cryptographic security. Depending on the situation, an attack may be possible on a secure protocol designed by predicting sensitive parameters such as an encryption key, and encrypted messages output by secure standard algorithms can be decrypted with a predicted key. Random numbers generated through encryption algorithms should not only be unpredictable for future values based on current values but should also prevent inferring past records. Since random number generation algorithms are generally publicly available, the input values (entropy sources) of the algorithm must remain confidential to ensure the unpredictability of values [5,6].  
Since cryptographic systems frequently use random numbers, secure random numbers within the system must be generated quickly. However, obtaining random numbers for cryptographic purposes without a separate algorithm is impossible, and even if a generator can produce unpredictable values each time it outputs (a true random number generator), its speed may not meet the required availability. For this reason, deterministic algorithms are used in cryptography to generate secure random numbers quickly. The algorithm used in this case is called a deterministic random bit generator (DRBG), which generates random numbers according to a predetermined logic based on the input seed [7]. Therefore, if the same seed is set for the identical DRBG, the output values are exactly the same. Due to this characteristic, if the algorithm user uses a predictable value as the seed, an attacker can accurately determine the random numbers generated by the user. Therefore, the seed used to initialize or update the DRBG must be unpredictable and different every time. Generally, the seed is composed of noises that can be easily obtained in the operating environment [8; 9; 10; 11].