question: public static String gensalt ( int log_rounds , SecureRandom random ) { if ( log_rounds < 4 || log_rounds > 31 ) { throw new IllegalArgumentException ( "Bad number of rounds" ) ; } StringBuilder rs = new StringBuilder ( ) ; byte rnd [ ] = new byte [ BCRYPT_SALT_LEN ] ; random . nextBytes ( rnd ) ; rs . append ( "$2a$" ) ; if ( log_rounds < 10 ) { rs . append ( "0" ) ; } rs . append ( log_rounds ) ; rs . append ( "$" ) ; encode_base64 ( rnd , rnd . length , rs ) ; return rs . toString ( ) ; }
target:  Generate a salt for use with the BCrypt.hashpw() method