Maybe you remember the old software distribution models. People had obtained a trail version and bought a software key afterwards which means they received a combination of alphabetic and numeric characters and activated the full version. Other folks usually found a way how to circumvent that procedure plus developed software to let others do so again. I just took a deeper look into one of those tools and it was really disappointing:
$ objdump -Dj .text keygen | grep '<.*>:' 08048410 <_start>: 08048434 <call_gmon_start>: 08048460 <__do_global_dtors_aux>: 080484a0 <frame_dummy>: 080484d4 <_Z5crc32mPhj>: 0804864c <_Z9getserialPc>: 080486cc <main>: 080487f0 <__libc_csu_init>: 08048850 <__libc_csu_fini>: 080488a0 <__i686.get_pc_thunk.bx>: 080488b0 <__do_global_ctors_aux>:
Apparently the program does nothing else then using a simple cyclic redundancy check which is equal to the following ruby code:
#!/usr/bin/env ruby require 'zlib' print 'Name: ' puts "Serial: %X" % Zlib::crc32('StudioEnterprise' + gets.strip + '12182039') + '12182039'
I had to reverse engineer the whole program to make sure there is no magic in it. There isn’t. Check out the Wikipedia if you want to know more about the division in the ring of polynomials over the finite field $ (Z_2,+,\cdot) $.