Ninety Nine Nights 2

"
Security:
-> Custom XOR Encryption
-> Custom Checksum (2x)
"

private void Encrypt(byte[] data, int offset, int size) {
    int next = 0;
    for (int i = offset; i < (offset + size); ++i) {
        next = ((data[i] ^ next) + (i - offset)) ^ 0xBB;
        data[i] = (byte) next;
    }
}

private void Decrypt(byte[] data, int offset, int size) {
    int last = 0, next;
    for (int i = offset; i < (offset + size); ++i) {
        next = ((data[i] ^ 0xBB) - (i - offset)) ^ last;
        last = data[i];
        data[i] = (byte) next;
    }
}

private int CalculateChecksum(byte[] data, int offset, int size) {
    int sum = 0;
    for (int i = offset; i < (offset + size); ++i)
        sum += data[i] ^ (i - offset);

    return sum;
}

"
Read Save:
"

byte[] data = File.ReadAllBytes(fileName);
Decrypt(data, 0x34, 0x3560);

"
Write Save:
"

byte[] data = File.ReadAllBytes(fileName);
using (var xIO = new MasterIO(data, Endian.BIG)) {
    xIO.Position = 20;
    xIO.Writer.WriteInt32(CalculateChecksum(data, 0x34, 0x3560));
    xIO.Writer.WriteInt32(0);

    xIO.Position -= 4;
    xIO.Writer.WriteInt32(CalculateChecksum(data, 0, 0x34));
    Encrypt(data, 0x34, 0x3560);
}