In a Nutshell

This is an implementation of finite set encryption algorithm. Basically it creates a cryptographic bijective mapping between two identical finite sets. In practise this can be used for example mapping a range of integers (e.g. 0..10000000) to the same range but in pseudorandom order. The mapping is keyed and cryptographically strong, so with a different key, the mapping is also different.

Reference

Fsmixer(key, setSize)

const Fsmixer = require('fsmixer');
const BitBuf = require('bitbuf');
const assert = require('assert');

var m = 13;
var x = new Fsmixer('verysecret', m);
for (var i = 0; i < m; i++) {
    var j = x.encrypt(i);
    var k = x.decrypt(j);
    console.log(i, j, k);
    assert.equal(i, k);
}

var m = 13;
var x = new Fsmixer('verysecret2', m);
for (var i = 0; i < m; i++) {
    var j = x.encrypt(i);
    var k = x.decrypt(j);
    console.log(i, j, k);
    assert.equal(i, k);
}

Just figure it out.

About Data Types

The data set size is passed to the constructor as number, which must pass the check with Number.isSafeInteger() and be greater or equal to two, or as a string representing a decimal integer greater or equal to two, or BigBum object again greater or equal to two.

If the data set size is greater than what can pass the check with Number.isSafeInteger() (i.e. 2^53-1), it must always be passed as a string or BigNum.

Encrypt and decrypt methods return an integer. If the sata set size is smaller or equal than 2^53-1, it is returned as a number. If however the data set size is greater than 2^53-1, both methods, encrypt and decrypt, always return a BigNum instead of a number. This solely depends on the actual size of the data set, not the type of the variable with which it was passed to the constructor.

References

This is original work, but the finishing touches are somewhat inspired by a publication from Terence Spies [email protected].

https://csrc.nist.gov/csrc/media/projects/block-cipher-techniques/documents/bcm/proposed-modes/ffsem/ffsem-spec.pdf

Author

Timo J. Rinne [email protected]

License

GPL-2.0