BKS File

What are BKS files and how to open them

Are you having problems opening a BKS file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your BKS files.

What is a BKS file?

BKS files have multiple uses, and BouncyCastle Key Store is one of them. Read more about the other uses further down the page.

BouncyCastle Key Store

The BouncyCastle Key Store is a file format used in Java (and Android) applications to securely store cryptographic items such as private keys, public keys, trusted certificates, and secret keys. The format is implemented by the Bouncy Castle cryptographic library and often bears the extension .bks. These files serve as keystores or truststores: a keystore holds private key(s) with their certificate chain(s), while a truststore contains only trusted certificates.

A program called KeyStore Explorer can both create and modify .bks keystores. Users generate a keystore by choosing the BKS type, assigning a password, and adding entries - these may include private key entries (protected by the keystore password and an entry-specific password), trusted certificates, or secret keys. Once populated, the keystore is saved in the .bks format. Other tools that rely on the Bouncy Castle provider (such as Java's keytool when configured appropriately) can load or convert these files, extract certificate chains, change passwords, and migrate entries to other keystore formats.

There are two major versions of the BKS format: version 1 ("BKS-V1") and version 2. Version 1 was used in older releases of Bouncy Castle (up to version 1.46), but had a weakness: its keystore-level integrity uses a very short (16-bit) HMAC, making it vulnerable to trivially forged integrity checks. Starting in Bouncy Castle 1.47, the default BKS format was changed to version 2, which uses a full 160-bit SHA-1 based MAC instead. In later versions (from 1.49 onwards), "BKS-V1" is still supported only for legacy compatibility.

Technically, a BKS file is a binary structure that begins with a four-byte integer indicating the format version. It ends with a null byte followed by a SHA-1 hash (20 bytes) which serves as a message authentication code (MAC) for the keystore contents. These layout details apply to version 2; version 1 uses a truncated MAC.

How to open BKS files

We have identified one BKS opener that is compatible with this specific type of BKS file.

Programs that open BouncyCastle Key Store files

Last updated: August 24, 2026

All known file formats using extension .BKS

While BouncyCastle Key Store is a popular type of BKS-file, we know of 3 different uses of the .BKS file extension. Different software may use files with the same extension for different types of data.

IBM BookManager BookShelf

IBM BookManager BookShelf is a format used by IBM BookManager and IBM Softcopy Reader to represent a logical bookshelf: a curated list of one or more books grouped for easier browsing and searching. A bookshelf file stores metadata such as book titles, file names, authors, last updated date, and often the location of an associated search index; its primary role is to help users organize and access related BookManager book files.

These files are created by the BookManager toolset (including BUILD and READ components) and by IBM Softcopy Reader. Users (or administrators) define which books belong to each bookshelf, and then the file is used to navigate among those books and perform searches across them. For IBM's softcopy collections, bookshelves can include books in the proprietary BookManager format and may also reference PDF documents when using an extended shelf feature. The bookshelf is often indexed via a companion index file to speed up full-text searches across all contained books.

Textual in nature, the bookshelf file begins with the ASCII signature "BKSHELF=" at its very start. It contains internal tags such as BKIDATETIME, BKNAME, BKSDATETIME, BKDATETIME, BKIBOOKS, BKSINDEX, BKSLEXIS, BKSTITLE, BKFLAG, BKNAME, which mark fields like the bookshelf's title, the books it refers to, its date metadata, flags, and indexing references.

While we have not verified the apps ourselves yet, our users have suggested three different BKS openers which you will find listed below.

IBM Softcopy Reader (Bookmanager) Book File

IBM Softcopy Reader Bookmanager Book File is a bookshelf definition used by IBM's BookManager system, mainly by the Softcopy Reader software. It organizes a logical grouping of books or documentation topics so that related materials can be browsed or searched together. The file specifies which BookManager books are included, their titles, descriptions, and where they are located in a directory or network setup. It is not the book content itself but a catalog for referring to books from a shelf.

This format is created by BookManager Build tools or by Softcopy collection kits, and is used together with IBM Softcopy Reader (which comprises Book Reader and Shelf Organizer components). Shelf Organizer reads the bookshelf file to display the list of books, manage their organization (by name, date, title), locate the physical files, and enable searches across all books in the shelf. When an associated index file (.BKI) exists, the Software can use it to speed up searches through the entire bookshelf.

Files in this format are text-based; they list book file names, descriptions, and path locations. A bookshelf file bears the extension .bks, and it includes metadata such as bookshelf title, name, date last updated, and may reference a search index. A bookshelves structure defined in a .bks file can span multiple directories and include books physically stored in different collection paths.

The file begins with an ASCII signature, commonly "BKSHELF=" at offset 0, and uses internal field labels such as "BKNAME", "BKFLAG", "BKSTITLE", "BKSINDEX" to mark entries for each book. It also contains timestamps fields like "BKDATETIME" or "BKIDATETIME" among others. This signature and keyword structure helps identify the file as belonging to this specific format.

Various apps that use files with this extension

These apps are known to open certain types of BKS files. Remember, different programs may use BKS files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about BKS file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.