Encryption.md

Save File Encyption

Progression (save) files in Mediocre games are encrypted, but usually with very weak encryption (e.g. ciphers that have been known to be broken for centuries).

Background

In the user data folder for Smash Hit, there are a few different files: one for achivements, one for the configuration, quicksave info, key.dat and the save progression file.

The save progression file is progression.xml and is the only encrypted file.

Helpful knowledge

The encryption is essentially just a Vigenère cipher applied in addition to a Cesar cipher. (Yes. Please click the links.)

To explain it in short:

• Cesar chiphers work by taking each byte in a message and adding a constant value to it, called the shift. For example, you could have the message be the digits 5902359 and shift each character in it by one which results in 6013460.
  • Note that the arithmetic is modular ("clock face arithmetic"), so you "cut off" any extra digits or bits you don't need. For example 9 + 1 = 10, but we only the the first digit, so it's 0.
• Vigenère ciphers work simiarly, but change according to a repating key instead of one constant value. For example, you might have the message 5902359 and then the key 14. The key will expand out to 1414141 to repeat as long as the message, and then the two are added to get the encrypted text:

	5	9	0	2	3	5	9
+	1	4	1	4	1	4	1
-	-	-	-	-	-	-	-
	6	3	1	6	4	9	0

Encryption

For the byte at index n, the chipertext is Key[n % KeyLength] + (PlaintextLength & 0xff) added to the original byte. (Or to say it differently: that is the keystream at each byte.)

Mathematical description

Given a plaintext $p$ (of length $|p|$) and a key $k$ (of length $|k|$), the encryption function $e(p, k)$ encrypts a byte of plaintext $p_i$ as:

$$e(p, k) = (p_i + (k_{i \mod |k|} + |p|)) \mod 256$$

Given a ciphertext $c$ (of length $|c|$) and a key $k$ (of length $|k|$), the decryption function $d(c, k)$ decrypts a byte of plaintext $c_i$ as:

$$d(c, k) = (c_i - (k_{i \mod |k|} + |c|)) \mod 256$$

Keys

For quick reference, here are the keys for some of the games:

Game	Key	Unleetspeaked
Sprinkle	HulT3T__R0ck5!	Hultet Rocks!3
Sprinkle Jr	HulT3T__R0ck5!	Hultet Rocks!3
Sprinkle Islands	0u1er0ck5	Ouie rocks
Granny Smith	gr4nny0n5k47es	Granny On Stakes
Smash Hit	5m45hh1t41ght	Smash Hit Aight
Beyondium	d1r4c15Da5h1T	DIRAC Is Da Shit2
Does not Commute	d035n0tc0mmut3inl33t	Does not commute in leet
PinOut	n01t15ntp1n0ut1s	No it isn't, PinOut is

1. The free versions of the first few games appear to share the encryption keys with their paid versions.
2. DIRAC was the former name of Beyondium.
3. Not sure what it means.