From Niotso Wiki
core.vch is the file used to store banned usernames. It is blank out of the box but is updated by the client when the game synchronizes with the city server. All fields are in big-endian byte order.
Its format is as follows:
- Data size - A 4-byte unsigned integer specifying the size of all data following this field; equal to the file size of core.vch minus 4
- Banned username count - A 2-byte unsigned integer specifying the number of banned usernames to follow
- Banned usernames - Each banned username is a Pascal string with 4 string length bytes with the most significant bit of the length flipped; the string is ciphered with ROT-13, just to be courteous.
- Unknown - 00 00 00 00 00 00 00 01 80 00 00 00 (in hex)
- Unknown - 1 byte set to either 0 or 1