CVE-2018-5382

The default BKS keystore use an HMAC that is only 16 bits long, which can allow an attacker to compromise the integrity of a BKS keystore. Bouncy Castle release 1.47 changes the BKS format to a format which uses a 160 bit HMAC instead. This applies to any BKS keystore generated prior to BC 1.47. For situations where people need to create the files for legacy reasons a specific keystore type "BKS-V1" was introduced in 1.49. It should be noted that the use of "BKS-V1" is discouraged by the library authors and should only be used where it is otherwise safe to do so, as in where the use of a 16 bit checksum for the file integrity check is not going to cause a security issue in itself.

The first version of a BKS file contains a design flaw in the determination of the key size used to protect the data inside of the keystore. A SHA-1 hash function, which is 160 bits in length, is used in the BKS HMAC code. In a RFC7292-compliant cryptographic algorithm, the MAC key size is the same size as the hash function being used. This means that the MAC key size should be 160 bits long for BKS files. However, the Bouncy Castle code for version 1 BKS files uses only 16 bits for the MAC key size. This means that regardless of password complexity, a BKS version 1 file can only have 65,536 different encryption keys. A valid password for a keystore can be brute-forced by attempting each of these key values, which can take only seconds.