As a 7z archive, it supports AES-256 encryption , large file sizes (up to 16 exabytes), and "solid" compression, where multiple similar files are grouped to save more space. How to Access the Content
The "b1" prefix strongly suggests a connection to the B1 Free Archiver project. This tool uses its own format ( .b1 ) but also supports and produces standard .7z files. b1db.7z
Since it is a standard 7z-compliant file, you do not need the specific B1 software to open it. You can use: As a 7z archive, it supports AES-256 encryption