The SALT usually is private and they could be store in the code or in the OS. I fact, I don’t know why it shouldn’t be private.
If one of then (code or OS) is vulnerated then it’s game over, no matter if the information is secret or not. Why? Simple, the hacker could write a “call to home” or “log a text file with every user and password”.
The main problem of a simple salt is hacker could know the key so he could guess the SALT (and vulnerating the whole system).
Let’s say the encryption is simple MD5(SALT+KEY) and the key is 911.
It is the encryption: 28456ed50235b894b55239a6491534b3
And we try force brute:
- a911 -> 7f40a739acbc8a018388329cbc26207d
- b911 -> e82b3127a3dcb54006a068f97e9f2137
- c911 -> 91f5403cacd34744a8fde575541c7d8e
- ….
- (and finally) spiderman911 and it matches (ends with 911 and it’s the md5) -> 28456ed50235b894b55239a6491534b3
The SALT then is “spiderman”
But other SALTs could also matches, for example
- sadk34383scjklHOID>hoirghsd6554679rd9ew&)/=&323dsfid’gjkfdpo fgkrdpfkg´fpdkgdfkgfdkg´pdkfgdvfdgidfgqcxkc vñkc´bnpo43¿’911 -> 28456ed50235b894b55239a6491534b3 where “sadk34383scjklHOID>hoirghsd6554679rd9ew&)/=&323dsfid’gjkfdpo fgkrdpfkg´fpdkgdfkgfdkg´pdkfgdvfdgidfgqcxkc vñkc´bnpo43¿” this salt also matches!.
md5 has collisions, so there is an unlimited number of SALTs (because of collisions). However, one of them works for every case.
MD5 is trivial but it has 2'339'099'464'253'592'691 possible combinations. That’s it 2 exabytes. Google has around 100 exabytes in total, so 2 exabytes is a lot of information.
But, the number of combinations for SALTs are unlimited.
