Bcrypt Prefix

[Kangaroot]

Help to work out prefix for bcrypt hash to crack.

I have digest for bcrypt hash and know that it has 4 rounds, which doesn't explain me what prefix will have to come with hash.

$2a$10
$2a$13
$2y$10
$2b$10

Please anyone can explain which prefix have to be used?

[undeath]

if your cost factor is 4 (note: bcrypt does not have a iteration/round indicator) your prefix is probably $2y$4

[Kangaroot]

thank you