sjlver / psst Goto Github PK

The current page (under /docs/index.html) just redirects to GitHub. It would be a bit nicer to put some content there.

After 15 minutes of reading the documentation, I am 50% sure that each blank for the secret should contain a single letter out of the alphabet of 25 distinct tokens (with X and J merged together), although the gap is large enough for a short word.

I understand that for the author this is super-obvious, but me, as a causal visitor who is not familiar with Shamir's secret sharing (and uses this work to try to familiarize oneself with the concept), this piece of information is missing with no place even to deduce it.

If the ambiguity is there on purpose because e.g. there are several operating modes the psst can operate - e.g. a secret comprised from 25-level tokens, or just digits, or maybe some other type of data - please provide an example. That can be in a form of a photo of the filled in form. Even better yet would be an accompanying video of the process of filling in the form and then recovering the secret.

And thank you for sharing this! :-)

Currently, psst only has an A4 worksheet.

Description here: https://www.vice.com/en/article/jp5xwy/itll-take-more-than-glitter-nail-polish-to-stop-snooping

Essentially, glitter nail polish is a "physically unclonable function". To use it:

• Fold the shares
• Add some glitter nail polish
• Take a picture

Before secret recovery, compare the share to its picture to check whether the nail polish has been tampered with.

Something like this (from https://news.ycombinator.com/item?id=38963197)

The 25 rows of the table correspond to the 25 linear polynomials in GF(5), evaluated at x=0, 1, 2, 3, and 4.
GF(5) is the "field" that psst uses. It just means that all math is performed using only digits 0 to 4, and we take the remainder modulo 5 after each operation. A linear polynomial has the form ax + b. There are 25 of them because a and b can each take one of the five values.

For example, consider the polynomial 3x + 0. If you evaluate it at x=0, the result is 0. At x=1, it's 3. At x=2, it's 6, which corresponds to 1 in GF(5). At x=3, the result is 4, and at x=4, the result is 2. These values (0 3 1 4 2) form the fourth line in the table above.

The table on the first page of the worksheet and the table on each share all have the same rows. They are just sorted differently, to make it easier to lookup a given row.