question: public static String toBase58WithChecksum ( byte [ ] b ) { byte [ ] cs = Hash . hash ( b ) ; byte [ ] extended = new byte [ b . length + 4 ] ; System . arraycopy ( b , 0 , extended , 0 , b . length ) ; System . arraycopy ( cs , 0 , extended , b . length , 4 ) ; return toBase58 ( extended ) ; }
target:  Encode in base58 with an added checksum of four bytes.