Is it accurate to state that the IDEA algorithm remains unbroken by brute force?

The statement that the IDEA (International Data Encryption Algorithm) remains unbroken by brute force is accurate because the key size of the algorithm significantly contributes to its resistance against brute force attacks. IDEA uses a key size of 128 bits, which implies that there are a total of 2^128 possible keys. This enormous number of potential combinations means that, with current computing power and techniques, it is computationally inviable to attempt to brute force the encryption in a reasonable timeframe.

Brute force attacks involve systematically trying every possible key until the correct one is found. Given the astronomical number of keys, successfully executing a brute force attack on IDEA would require an impractical amount of time and resources, even with the most advanced computing technologies available today. Therefore, it's reasonable to state that, as of now, IDEA has not been broken by brute force methods, making it a secure choice in the context of symmetric encryption based on its design and key length.

The other options suggest varying levels of uncertainty or specificity, which do not align with the current understanding of IDEA's robustness against brute force attacks.