Need help with decrypting packets

What are you actually getting when you decrypt the first few bytes? Strings in rotmg packets have a short (Int16) before the actual string to indicate the length of the string. The build version string is 7 characters long, so the first 2 bytes of the decrypted hello packet should be 00 07. The build version itself will be the next 7 bytes, which are 58 32 31 2e 30 2e 32.

Thanks for those links, definitely going to check out them.

I'm getting bc f7 6f ef dd da 15 b2 b0. Obviously not the build version.

I'm starting to think that the rc4 implementation of the website is not correct or something like that. So I'll code my own, based on the ones the projects willfuttbuck sent use, and see how it goes.

You said you aren't counting the first 5 bytes for the build version, but are you still decrypting those 5 bytes anyway? The first 5 bytes are not encrypted so trying to decrypt them will advance the RC4 state too far and cause all subsequent decryptions to be wrong.

You mean the bytes indicating packet length and id? No, I'm not decrypting those. I know they are not encrypted.

In that case you're probably right about the website.
The RotMG_Clientless repo uses the openssl rc4 implementation, but the nrelay repo has its own implementation which is at src/crpyto/rc4.ts in case you want a reference.

Ok, the website is not the problem. I copied the exact same code of the KRelay's RC4 implementation and it gives me the same results as the website.

Are the keys really 311f80691451c71b09a13a2a6e / 72c5583cafb6818995cbd74b80? I transform them to bytes as an hex string, not an ASCII string. The same with the packet bytes: I copy the hex string from wireshark and transform them into bytes as an hex string, not an ASCII string.

Maybe the hello packet isn't really the first packet but I don't think so, wireshark tells me it's the first packet the client sends when you connect to the game.

Or maybe it has something to do with the byte order (BE/LE) but I don't know exactly how that works.

Figured it out, I don't know why but those keys are wrong lol. I have the right keys now.

Thanks for the help though!