@ネパリ サンデャ Thank you for reaching out to us, As I understand you are looking info on AIP (decryption can be done using password), I have researched on this also discussed with my team internally on your ask.
As far we are aware there is no information about using a password to decrypt RMS protection.
Below articles will help you to understand how AIP works
https://learn.microsoft.com/en-us/purview/encryption
https://learn.microsoft.com/en-us/azure/information-protection/how-does-it-work
Let me know if you have any further questions, feel free to post back.