B1 is an open archive file format that supports data compression and archiving^{[citation needed]}. B1 files use the file extension ".b1" or ".B1" and the MIME media type application/x-b1. B1 incorporates the LZMA compression algorithm.^[1] B1 archive combines a number of files and folders into one or more volumes, optionally adding compression and encryption. Construction of the B1 archive involves creating a binary stream of records and building volumes of that stream. The B1 archive format supports password-based AES-256 encryption.^[2] B1 files are created and opened with its native open-source B1 Pack Tool, as well as B1 Free Archiver utility.^[3][4]

B1 Pack Project

B1 Pack is an open-source software project that produces a cross-platform command-line tool and a Java library for creating and extracting file archives in the B1 archive format. Source code of the project is published at GitHub.^[5] B1 Pack Project is released under the Apache License.^[6] The B1 Pack Tool module builds a single executable JAR file which can create, list, and extract B1 archive files from a command-line interface.^[7]

B1 format features

• Support for Unicode names for files inside an archive.
• Archives and the files inside it can be of any size.
• Support for split archives, that consist of several parts.
• Integrity check with the Adler-32 algorithm.
• Data compression using the LZMA algorithm.
• Supports encryption with the AES algorithm.^[8]

API features

• Instant creation of an archive without reading from/writing to a file system.
• Producing only a byte range of an archive, e.g. for resuming downloads.
• Streaming archive content without prior knowledge of all the files being packaged.