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A reverse engineer's checksum toolbox

License: MIT License

Rust 95.83% C++ 3.78% Shell 0.39%

reverse-engineering checksums

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dtolnay-contrib ffy00 nx6110a5100 pfemidi tomspectre zzzdaxia

delsum's Issues

algorithm question

are there any plans to support other algorithms, for example, some like the SDBM hash? http://www.cse.yorku.ca/~oz/hash.html#sdbm

u32 sdbm_hash(const u8* data, u32 len, u32 init)
{
    u32 crc = init;
    
    while (len--)
        crc = (crc * 0x1003f) + *data++;

    return (crc);
}

Is this tool still compatible?

I noticed it's been a few years since the last release. Not sure if I'm doing something wrong in the installation. Using Cargo I get an error with funty

failed to select a version for the requirement "funty" = 1.2

unclear how to make use of this

In your article about IT8586E reversing, the checksum calculation procedure is unclear.

You say poly is 0x8005. I downloaded two EC dumps for the 15IKB device, one is actual dump, other is extracted from BIOS update file.

The delsum tool seems to work fine as i get same results with it as with windows HxD editor.
However, inputting 0x8005 and all other parameters as you suggest i end up with checksum that does not exist anywhere in EC dump.
Can you explain this part better? Is the checksum location in dump known and does it need to be cleared to FF before calculating checksum?

Support changing the handled data size

I am working with a CRC algorithm found in STM32.

Python algorithm:

words = struct.unpack('I'*data_len, data)  # unpack into 4 byte words

crc = 0xFFFFFFFF

for word in words:
    crc ^= word
    for _ in range(32):  # 0 .. 31
        if crc & 0x80000000:  # 32th bit is set
            crc = (crc << 1) ^ 0x04C11DB7
        else:
            crc = (crc << 1)
    crc &= 0xFFFFFFFF

# crc should hold the final value now

This is the algorithm implemented by the CRC peripheral. The description should be on page 6 of AN4187.

It looks to me like it is a derivation of the standard CRC algorithm but with a different size for the handled data. 32 bits instead of 8, correct?

If so, would it be possible to support this option?

Problem with reversing checksum algorithm of protocol messages

Hi, I have several ICMP messages and want to reverse the checksum algorithm of these messages using delsum. Here are some messages, shown in hex

08004ab69c480007648b1224000eaf3908090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f3031323334353637
080038fa9c480008648b1225000ec0f308090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f3031323334353637
080027409c480009648b1226000ed2ab08090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f3031323334353637

Since the checksum file of ICMP is 2-3 bytes (starting from 0).
First, I tried to convert each hex stream to a file, e.g., echo "08004ab69c480007648b1224000eaf3908090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f3031323334353637" | xxd -r -p > file1.

Then, I tried delsum by command

delsum reverse -m 'crc width=16 init=0' -c b64a,fa38,4027 file1 file2 file3

But there is no output. I'm not sure if I'm using delsum correctly. Could you please help me? Thanks so much.

4Bit checksum possible?

It is more a question than an issue, but I haven't found that information. Interpretation of that output

./delsum reverse -m 'crc width=4' -c E,D,8 file_a file_b file_c

Could not read checksums: Odd number of digits

makes me believe that it isn't at the moment.

Second in README.md it is given this example of part:

$ delsum check -m 'modsum width=16 module=ffff' -c 1234,5678,abcd file_a file_b file_c
modsum width=16 module=ffff:
    0x8:-0x3

I think the code should be:
$ delsum **part** -m 'modsum width=16 module=ffff' -c 1234,5678,abcd file_a file_b file_c

The same is for reverse where it is written:

$ delsum check -m 'crc width=32' -c 700b14f5,e1207917,79741cb2 file_a file_b file_c

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