It uses the XOR-cipher to compute a checksum digest. Basically, it splits the data in chunks whose length is the same as the digest size (padding with 0), and XORs all chunks between each other into a new chunk that's used as output.
This isn't a good hash function. It lacks the Avalanche Effect, because flipping 1 input bit flips 1 output bit.
The raw digest size is 64bit (8Byte) by default, but can be set to any valid usize value with the --length option. The actual size is bigger because the raw digest is expanded to hexadecimal by default. I choose 8, because CRC32 uses 4 and MD5 uses 16, and to make it easier for downgrade implementations to replicate, because 64b fits within a CPU register and can be emulated using 2 u32s
The initialization-vector is hardcoded to be 0
Both the naming and behavior are influenced by cksum, md5sum, and b3sum.
To install latest release from crates.io registry:
sh
cargo install xorsum
This isn't guaranteed to be the latest version, but it will never throw compilation errors.
To install latest dev crate from GH:
sh
cargo install --git https://github.com/Rudxain/xorsum.git
This is the most recent version. Compilation isn't guaranteed. Semver may be broken. And --help may not reflect actual program behavior.
To get an already-compiled non-dev executable, go to GH releases.
Argument "syntax" (any order is allowed, but it's good practice to place options near each other):
sh
xorsum [OPTION]... [FILE]...
For ℹinfo about options, run:
sh
xorsum --help
```sh
echo -n > a xorsum --length 4 a
echo -n aaaa > a xorsum a -l 4
echo -n aaaa | xorsum -l 4
xorsum a --brief #-l 8 is implicit
``
Note:echo -nhas [different behavior depending on OS and binary version](https://unix.stackexchange.com/a/65819), it might include line endings like\n(LF) or\r\n` (CR-LF). The outputs shown in the example are the (usually desired) result of NOT including a new-line.
PowerShell will ignore -n because echo is an alias of Write-Output and therefore can't recognize -n. Write-Host -NoNewline can't be piped nor redirected, so it's not a good alternative.
--length doesn't truncate the digest:
sh
xorsum some_big_file -b -l 3 #"00ff55"
xorsum some_big_file -b -l 2 #"69aa" NOT "00ff"
As you can see, -l can return very different hashes from the same input. This property can be exploited to emulate the Avalanche Effect (to some extent)
What if you have a file named "-"? ```sh echo bruh > -
OPTION, use "./" relative pathxorsum ./- ```
If you have 2 copies of a file and 1 is corrupted, you can attempt to "triangulate" the index of a corrupted byte, without manually searching the entire file. This is useful when dealing with big raw-binary files ```sh xorsum a b
-l 8xorsum a b -l 3
xorsum a b -l 2
-l values, to solve it easier.``
There are programs (like [diff`](https://en.wikipedia.org/wiki/Diff)) that compare bytes for you, and are much more efficient and user-friendly. But if you are into math puzzles, this is a good way to pass the time by solving systems of linear modular equations
I was surprised that I couldn't find any implementation of a checksum algorithm completely based on the XOR op. So I posted this for the sake of completeness, and because I'm learning Rust. I also made this for people with low-power devices
DO NOT USE FOR 🔐CRYPTOGRAPHIC PURPOSES. The algorithm is not crypto-secure
DO NOT SHARE HASHES OF PRIVATE DATA. You might be leaking sensitive information. Small hashes and bigger files tend to be safer, because the sbox will (probably) have enough bytes to "mix well"