Bukkit

*** As of Minecraft 1.2, Mojang removed the map seed from SMP! ***

*** It is no longer present in the 0x01 Login and 0x09 Respawn packets, therefore the offline seed attack which NoSeed protected against in 1.1 is no longer possible. ***

*** The cheat protection NoSeed provided is now part of the design of vanilla Minecraft, thanks to the new Anvil chunk format. NoSeed is now obsolete as of Minecraft 1.2.***

Ever want to hide the map seed?

Easily visible by opening the F3 debug screen, this number can be loaded into a new single-player game to create a nearly identical world offline to X-ray at your leisure, loaded into AMIDST to quickly find strongholds and villages, or other tools to gain an unfair advantage against other players.

NoSeed hides the true level seed from the F3 screen, replacing it with a random value having no relation to the actual seed. An effective anti-cheat measure.

Features:

• No client mods required
• No chunk re-generation needed
• No changes to your world save file
• Configurable in-game
• Permission support
• (Misfeature) Biome inaccuracies (see limitations below)

Installation

Important: NoSeed has not yet been updated for 1.1-R4. Only use with 1.1-R3 at this time.

To use NoSeed, you must add the -javaagent:plugins/NoSeed.jar command-line flag to CraftBukkit, as the very first argument. For example:

java -javaagent:plugins/NoSeed.jar -mx4G -jar craftbukkit-1.1-R3.jar

You can keep all your other flags, as long as -javaagent:plugins/NoSeed.jar is listed first.

If everything is working correctly, the first line of output will be:

[NoSeed] Initializing

Important: If this flag is missing, NoSeed will not function. You must be able to specify custom flags to use NoSeed.

Once NoSeed is installed, login to your server, and press F3. You should now see a fake seed in place of the real world seed. If desired, you can change the fake seed to your liking, see below.

Commands

/seed: View the fake seed, and the last real seed replaced. Requires noseed.get permission.

/seed [number]: Change the fake seed. Requires noseed.set permission.

/seed flat: Toggle between forcing Superflat and using the existing world type. Requires noseed.set permission.

All changes take effect immediately and will apply to new users logging in.

Permissions

noseed.set (op): Allows you to change the fake seed

noseed.get (op): Allows you to view the real seed

Configuration

fakeSeed: The fake seed to be used. This can be set using /seed in the game, or changed in config.yml. If no seed is given, a default pseudorandom number is generated and saved here on first use of /save.

lastRealSeed (read only): For convenience, the real seed which was last replaced is written here when you type /seed.

forceFlat: true to force the world type to Superflat, false to not override the world type. Superflat is on by default.

Limitations

Important caveat: Biome colors and weather may be unexpectedly changed.

You can try to workaround the problem by experimenting with different fake seeds and toggling forceFlat, but a complete fix requires client modification to obtain the biome data from the server, rather than generating it client-side from the seed.

Secondly, world generation is pseudorandom, not cryptographically secure. Theoretically, a sufficiently advanced attacker could reverse-engineer the actual seed from the map contents. So far, this attack has not been demonstrated (as far as I know) and is believed to currently only be theoretical.

See also

If the biome scrambling is untenable, you may find other anti-cheat plugins preferrable.

For example, ChunkScrambler uses a different seed for ore (etc.) generation, leaving biomes intact. NoSeed in contrast does not alter chunk generation, but rewrites the login packet to send a fake seed to the client, at the expense of accurate biome colors.

News 2012/02/10: "Biome data will be saved with the chunks in the new world format. " - _jeb. This would potentially allow the biome problem with NoSeed to be solved.

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