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(MrgOpener): guess index encryption key.

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This commit is contained in:
morkt 2015-07-14 17:47:13 +04:00
parent d312da7de5
commit f883d9d4af
1 changed files with 33 additions and 0 deletions
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33
ArcFormats/ArcMRG.cs
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@ -66,10 +66,17 @@ namespace GameRes.Formats.FC01
var index = new byte[index_size];
if (index.Length != file.View.Read (0x10, index, 0, index_size))
return null;
/*
var key_src = KnownKey;
if (key1index >= key_src.Item1.Length || key2index >= key_src.Item2.Length)
return null;
byte index_key = (byte)(key_src.Item1[key1index] + key_src.Item2[key2index]);
*/
var key = GuessKey (file, index);
if (null == key)
throw new UnknownEncryptionScheme();
byte index_key = key.Value;
int remaining = index.Length;
for (int i = 0; i < index.Length; ++i)
{
@ -132,6 +139,32 @@ namespace GameRes.Formats.FC01
}
return input;
}
private byte? GuessKey (ArcView file, byte[] index)
{
uint actual_offset = (uint)file.MaxOffset;
byte v = index[index.Length-1]; // last_offset
v = (byte)(v << 1 | v >> 7);
byte key = (byte)(v ^ (actual_offset >> 24));
int remaining = 1;
uint last_offset = (byte)(v ^ key);
key -= (byte)++remaining;
for (int i = index.Length-2; i >= index.Length-4; --i)
{
v = index[i];
v = (byte)(v << 1 | v >> 7);
last_offset = (last_offset << 8) | (uint)(v ^ key);
key -= (byte)++remaining;
}
if (last_offset != actual_offset)
return null;
while (remaining < index.Length)
key -= (byte)++remaining;
return key;
}
}
/// <summary>