1. Completely immutable
2. Could not be maliciously altered by the reader
3. Could not masquerade as a keyboard or a mouse
I've got some external USB readers/burners that excel for exactly this sort of thing, and just about anything that will run a modern OS will boot from them.
Admittedly this was almost 20 years ago at this point so maybe some things have improved since then but my understanding is that consumer media uses a different, ink-based technology to write data to disk, and that ink can degrade pretty quickly. This is in contrast to commercial optical media in which the data is stamped into the disk in a manner more akin to a vinyl record.
Some forms of writeable disc media don't use dyes and can last for over 100 years. Check out the link.
But, to your point, one of the variables that affect longevity is the quality of the manufacturing. If you're buying the least expensive media you can find, then the lifespan is indeed shorter. For my cheapo CD-Rs, I've found that they last 5-10 years. You can also make them last longer by storing them in better conditions (vertically, not laying flat, in an airtight container in the freezer).
I tend to go with cheap media, so my personal habit is to burn new copies of my storage discs every 5 years.
One variable I'm recently able to validate (wow, 20 years later!) is write speed. Discs written (for archival) at slower speeds still work. Discs I wrote as fast as possible on my way out the door have mostly failed by now.
Verbatim DVD-R UltraLife Gold Archival Grade 95355
Of course you need Reed Solomon across drives (Eg raidz) regardless of media
A modern computer is really a distributed system, but not a lot of people frame the discussion that way.
> The embedded microcontroller is typically a heavily modified 8051 or ARM CPU. In modern implementations, the microcontroller will approach 100 MHz performance levels, and also have several hardware accelerators on-die.
Wouldn't the laser of a CD/DVD writer be powerful enough to alter the data after the fact? Not to overwrite it with completely arbitrary data, but flipping a few well-chosen bits should in principle be able to create a backdoor that wasn't there before (if it's a live or install disk, for example).
The issue here is that you can't "unburn" a bit that has been burned. Since you burn 0s, not 1s, all you can do is make more bits 0 -- which would then be corrected by the error correction mechanism. You could alter the EC codes, but that would render them useless and eliminate the ability to correct errors, causing the data to be unreadable by a normal drive due to EC failure.
So, in practice, they're pretty safe. The worst thing that an attacker could do is to render the media unusable.
I don't remember if it required the disc to be un-finalized or not. It probably did.
But this is really an edge case
If not, then you "just" have to find the right spots where such a simultaneous alteration of the payload and the EC code is possible, and which also happens to result in a desirable behavior change.
So you'd have to find mutations that are big enough to not be automatically corrected (more than 2 bits, you can't change, say a single 0x30 to 0x31), and also happen have the right signature so they don't flag as erasures, so you can't freely change bytes to just anything. And then you have to also satisfy the outer code that your modified byte after interleaving is correct. And do it all by only bring able to bit-flip in one direction. The only upside is that you can also flip bits in the correction bytes if you need.
Also, if the data you're modifying has any coding or compression (ZIP, Word documents, videos, most images), or there are checksums, you have to not upset that. And if it's encrypted, you won't know what to change in the first place.
So it's theoretically possible, but it would be very tricky and highly unlikely that you could change a useful piece of data unless you were extremely lucky with what the data was, what you wanted it to be, and where it was on the disk.
If you're concerned about people modifying your CD-R: encrypt and SHA-256 the whole thing and you'll be fine. I assume this threat model mostly targets governments, so they should first do both of those things and maybe also stop leaving them on trains.