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 5, 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

We know that one BKS format is IBM BookManager BookShelf. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

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

We know that one BKS format is IBM Softcopy Reader (Bookmanager) Book File. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

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

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