Cloudera Docs

Bcrypt

  • This KDF was added in v0.5.0.

  • https://en.wikipedia.org/wiki/Bcrypt is an adaptive function based on the https://en.wikipedia.org/wiki/Blowfish_(cipher) 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 https://en.wikipedia.org/wiki/General-purpose_computing_on_graphics_processing_units (which share memory between cores) by requiring access to "large" blocks of memory during the key derivation. It is less resistant to https://en.wikipedia.org/wiki/Field-programmable_gate_array 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 http://blog.ircmaxell.com/2012/12/seven-ways-to-screw-up-bcrypt.html. 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.