sum32: Compute the 32-bit FITS 1’s complement checksum

Package: fitsutil

Usage

sum32 input

Parameters

input [string]

A list of files, often but not exclusively FITS images.

verbose = no

Report verbose information for each file?

nimages

[Output] The number of images in the input list.

Description

SUM32 computes the 32-bit 1's complement checksum for a list of files. This is the algorithm used for the standard FITS checksum [1]. Any 32-bit checksum will generate a 10 digit hash value. The special feature of the 1's complement checksum is that this hash is straightforward to invert (and thus is not suited to protect against explicit mischief).

Since the checksum can be computed, it is possible to force a file's checksum to a specific value. Without this feature it would be impossible to convey a checksum within the original file. Files (typically FITS) that have been so treated will be reported as "sum_zeroed" in the task output. The file size in bytes is also reported.

Examples

1. Report the 1's complement checksum for a list of files:

fitsutil> sum32 *.fits
sum_zeroed       584640 test1.fits.fz
1363490151       532800 test2.fits
2002849261       172800 test3.fits

References

[1] http://fits.gsfc.nasa.gov/registry/checksum.html