https://answers.microsoft.com/en-us/msoffice/forum/all/what-is-the-encryption-algo-used-for-password/34966ce1-933d-4c51-a5e9-12ee19943758#:~:text=Excel%20uses%2

https://answers.microsoft.com/en-us/msoffice/forum/all/what-is-the-encryption-algo-used-for-password/34966ce1-933d-4c51-a5e9-12ee19943758#:~:text=Excel%20uses%20Advanced%20Encryption%20Standard,encrypt%20the%20password%2Dprotected%20workbook. https://answers.microsoft.com/en-us/msoffice/forum/all/what-... They apparently use AES-128. Not quite the level of Bitwarden, which uses hashing (argon2 or PBKDF2) and AES-CBC-256 simultaneously.