Bcrypt

This KDF was added in v0.5.0.

Bcrypt is an adaptive function based on the Blowfish cipher. This KDF is recommended as it automatically incorporates a random 16 byte salt, configurable cost parameter (or "work factor"), and is hardened against brute-force attacks using GPGPU (which share memory between cores) by requiring access to "large" blocks of memory during the key derivation. It is less resistant to FPGA brute-force attacks where the gate arrays have access to individual embedded RAM blocks.

Because the length of a Bcrypt-derived hash is always 184 bits, the hash output (not including the algorithm, work factor, or salt) is then fed to a SHA-512 digest and truncated to the desired key length. This provides the benefit of the avalanche effect over the input. This key stretching mechanism was introduced in Apache NiFi 1.12.0.

The recommended minimum work factor is 12 (212 key derivation rounds) (as of 2/1/2016 on commodity hardware) and should be increased to the threshold at which legitimate systems will encounter detrimental delays (see schedule below or use BcryptCipherProviderGroovyTest#testDefaultConstructorShouldProvideStrongWorkFactor() to calculate safe minimums).

The salt format is $2a$10$ABCDEFGHIJKLMNOPQRSTUV. The salt is delimited by $ and the three sections are as follows:

• 2a - the version of the format. An extensive explanation can be found here. NiFi currently uses 2a for all salts generated internally.

• 10 - the work factor. This is actually the log2 value, so the total iteration count would be 210 (1024) in this case.

• ABCDEFGHIJKLMNOPQRSTUV - the 22 character, Radix64-encoded, unpadded, raw salt value. This decodes to a 16 byte salt used in the key derivation.