On Android Space RPG3 (free) and Space RPG4 ($3?) are really good spiritual successors as well.

Some of the original team are also working on a spiritual successor. Have been for a while. Don't remember what it's called though.

The New System

As Ambrosia's Matt Slot explains, the old system continued to allow a lot of piracy, so in the early 2000's they decided to switch to a more challenging registration system. This new method was based on polynomial hashing and included a timestamp so that codes could be expired and renewed. Ambrosia now had better control over code distribution, but they assumed their renewal server would never be shut down...

They also took more aggressive steps to reduce key sharing. The registration app checks against a list of blacklisted codes, and if found to be using one, the number of licenses is internally perturbed so that subsequent calculations fail. To combat tampering, your own information can get locally blacklisted in a similar manner if too many failed attempts occur, at least until the license file is deleted. Furthermore, the app attempts to verify the system time via a remote time server to minimize registration by changing the computer's clock.

You can disable the internet connection, set the clock back, and enter codes. There's also a renewal bot for EV: Nova. But let us look at the algorithm more closely.

64-bit Codes

The first noticeable difference is that registration codes in v2 are now 12 digits, containing both letters and numbers. This is due to a move from a 32-bit internal code to a 64-bit one. Rather than add an ASCII offset to hex digits, every letter or number in a new registration code has a direct mapping to a chunk of 5 bits. Using 5 bits per digit supports up to 32 values, or almost all letters of the alphabet and digits up to 9 (O, I, 0, and 1 were excluded given their visual similarities).

The resulting 64 bits (really only 60 because the upper 4 are unused: 12 digits * 5 bits each = 60) are a combination of two other hashes XOR'd together. This is a notable change from v1 because it only used the registration code to verify against the hashing algorithm. Only the licensee name, number of copies, and game name were really used. In v2, the registration code is itself a hash which contains important information like a code's timestamp.

Two Hashes

To extract such information from the registration code, we must reverse the XOR operation and split out the two hashes which were combined. Fortunately, XOR is reversible, and we can compute one of the hashes. The first hash, which I'll call the userkey, is actually quite similar to v1's algorithm. It loops through the licensee name, adding the ASCII value, number of copies, and shifting bits. This is repeated with the game name. An important change is including multiplication by a factor based on the string size.

The second hash, which I'll call the basekey, is the secret sauce of v2; it's what you pay Ambrosia to generate when registering a product. It is not computed by the registration app, but there are several properties by which it must be validated.

The chart below visualizes the relationships among the various hashes, using the well-known "Barbara Kloeppel" code for EV: Nova.

TEXTCODE:
------------------
| L4B5-9HJ5-P3NB |
------------------                    HASH1 (userkey):
	|                             calculated from licensee name,
        |                             copies, and game name
BINCODE:                              ----------------------
5 bits per character,             /-> | 0x0902f8932acce305 |
plus factors & rotations         /    ----------------------
----------------------          /
| 0x0008ecc1c2ee5e00 |   <-- XOR
----------------------          \
	                         \    ----------------------
	                          \-> | 0x090a1452e822bd05 |
	                              ----------------------
	                              HASH2 (basekey):
	                              generated by Ambrosia,
	                              extracted via XOR