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Library and CLI for computing O(K)Hash checksums.

Project description



O(K)hash (pronounced OK hash or oꭓash) is a hash function with $O(1)$ complexity based on SHA-256. It is designed to efficiently calculate hashes for large files by reading only a fixed subset of data from random positions within the file. The 'K' parameter denotes the strength of the hashing, with lower values reading less data. For example, a hash with K=1 reads only 1KiB of data, while a hash with K=2 reads 1MiB of data. The hash results are downgradable, meaning a hash of strength K=3 can validate a file hash calculated with K=1.


Calculating the hash of a large file normally involves reading the entire file, which can be time-consuming, especially with slow I/O operations. O(K)hash addresses this issue by reading a fixed number of bytes from random positions inside the file, providing a constant time complexity of $O(1)$. This approach generates a reliable fingerprint for identifying duplicate files and validating files efficiently.


After all, it's just an OK hash:

  • Not Suitable for Detecting Corruptions: O(K)hash is not suitable for detecting file corruptions that do not change the size of the file. In the case of a bit flip or small corruptions, the probability of detecting corruption is lower than: $\frac{base size}{file size}$.
  • Consider File Size Checking: Depending on the nature and number of large files you are working with, it may be more effective to check the file size before calculating a conventional hash to ensure data integrity.



You can install O(K)hash using pip:

pip install okhash


  • Calculate O(K)Hash of a String:

    import okhash
    data = "Hello, world!"
    checksum = okhash.okhash(data.encode('utf-8'), K=3)
  • Calculate & compare O(K)Hash of Files:

    import okhash
    file1_checksum = okhash.okhash_filepath("file1.bin")
    file2_checksum = okhash.okhash_filepath("file2.bin")
    if okhash.compare_okhashes(file1_checksum, file2_checksum):
        print("Checksums match.")
        print("Checksums do not match.")

Command Line Usage

  • Calculate Checksums: To calculate checksums for a file with a specified K value (default is K=2), use the following command:

    python3 -m okhash -K 3 file.bin
  • Check Checksums: The result of the previous command can be used to check checksums for multiple files:

    python3 -m okhash *.bin > okhashes.txt
    python3 -m okhash --check okhashes.txt
  • Additional Options:

    python3 -m okhash --help

The Strengths (K)

Here's a table describing the strengths (K) and their corresponding parameters:

K Base Size (Subset Data Size for Hash Calculation) Block Size
1 1024 B = 1 KiB 1024 B
2 1048576 B = 1 MiB 4096 B
3 1073741824 B = 1 GiB 262144 B
4 1099511627776 B = 1 TiB 16777216 B
K $2^{10K}$ $1024 \times \lceil \frac{2^{6K}}{1024} \rceil$

The minimum file size for a given K is equal to twice the base size; otherwise, the hash calculation will resort to SHA-256 for the entire file.


O(K)hash is released under the MIT License.

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