floph - the Floppy Hasher

This is a C64 tool to hash files or whole disks directly on the 1541 floppy, using 64 bit FNV-1a. So it allows to check integrity on real original hardware. It could for example be used to verify hashes after downloading some disk images and transfering them to a physical floppy disk, given the publisher also published a floph (FNV-1a) hash to compare to.

IMPORTANT: FNV-1a is not a cryptographically secure hash function. Such a hash function (e.g. SHA-256 or SHA-512) would be required to protect against intentional, malicious tampering, but those functions are impossible to implement on a 1MHz MOS-6502 machine with limited RAM.

With FNV-1a, you should assume collision attacks are feasible for a determined attacker, so expect this tool to only protect against accidental corruption, e.g. "bitrot".

Features

• Hash any regular, non-locked and not opened file of type PRG, SEQ or USR.
• Hash a whole disk (currently only standard 35 tracks).
• Detect and identify available drives on startup.
• May run on any 1541, 1570 or 1571.
• A simple TUI allows to select a file or the whole disk using cursor keys and start hashing with <RETURN>.
• Clean exit is always possible with <RUN/STOP>.
• Show a progress bar while hashing. For files, this can only be correct if the number of blocks in the directory was correct.

Hashing a whole disk uses a fixed sector interleave of 11. In this mode, most errors are tolerated, if they occur, the error code is hashed instead of the sector contents. This should allow to correctly hash disks that e.g. use errors for copy protection purposes.

After detection and identification of connected drives, a little menu is shown, allowing to pick any supported drive, or cancel and exit without uploading and starting floph's drive code.

Screenshots

Missing (future) features

Here's a rough list of what to possibly add later:

• Configurable number of tracks for whole-disk hashing, to allow 40- and 42-track disks.
• Persist a pre-calculated whole-disk hash in some unused area of the BAM, allowing an automatic verify later.
• For file hashes, maybe persist them in some regular (SEQ?) file.

pfloph, the "PC Floppy Hasher"

Included with floph comes a little C program allowing to calculate the same hashes of plain files or d64 disk images on the PC command line.

Usage:

pfloph [-d] [file]

• -d: Select "disk mode", input is expected to be a d64 image.
• file: The file to hash, if omitted, it is expected on standard input to allow usage with pipes.

Building

Build requirements:

• GNU make
• A C compiler (for pfloph)
• cc65
• c1541 from vice (for creating test disks)

To build floph.prg and pfloph, just type

make

A disk image for testing (with lots of files added) can be created with

make disk

For the same disk, but containing a single sector error, type

make errdisk