Question: How to determine the max. number of digits `encryptNumber()` will return? about feistel-cipher

[cyrildever]

Hi @anthonylau,
Actually, the library doesn't provide a way to do it directly.

You should do it yourself by using some sort of wrapping function, eg. if you want a 10-digit length number with 0 padding:

const pad10Zero = (numberToPad: number): string => numberToPad.toString().padStart(10, '0')
const encryptedNumber = 987654
// 0000987654
console.log(pad10Zero(encryptedNumber))

Beware that the encrypted padded number is now a string, not a number anymore. It is just meant to be used in text, not for calculus.

Hope it helps.

[anthonylau]

Hi @cyrildever,

Thanks for the reply. What I want to know is the max. length of the encryptedNumber() result for a given input. So that I can have a fixed length output which never exceed the predefined size. For example,

encryptNumber(1).toString().padStart(5); // output: 00123
encryptNumber(2).toString().padStart(5); // output: 123456 , exceed length 5 which is unexpected

My use case is, encrypt a number and within a certain range. For example, given input 1234, the output should be within 0-99999.

[cyrildever]

Hi @anthonylau,
Unfortunately, there is no way to predetermine that considering the library don't know what's coming into it. But, normally, an incoming 6-figure number should return a 6-figure max number (considering 123456 could return 123, ie. 000123). Tell me if you see it otherwise.
So, it all depends on your knowledge of your incoming data.