mysto / node-fpe Goto Github PK

Larger radix values are currently failing with a primitive number issue. Radix is the size of the alphabet used, so numerics (0..9) is Radix 10 and mono-case English would be Radix 26. It fails with Radix is 20 or more due to overflow.

JavaScript represents all numbers in double precision floating point and has a range of +/- 2^53 for the mantissa. For example,

> Math.pow(2, 53)        // OK
9007199254740992
> Math.pow(2, 53) + 1  // not OK
9007199254740992

The solution is to use BigNum. For this, the Math.pow function needs to be implemented directly as a function instead of using the math library using numbers. I tried a recursive version, but that blew the stack. So, a simple loop is likely what's needed.

Or perhaps we can use the ** operator:

2n**63n-1n
9223372036854775807n

See also:

• https://github.com/tc39/proposal-bigint

Hi, I tried to make the library compatible with the browser environment, and since BigInt only works on iOS14+, I used the big-integer library(https://www.npmjs.com/package/big-integer) as a polyfill.

I modified the following in FF3Cipher.js to support running scripts:

add require:
const BigInt = require("big-integer");
change line 45:
0n => BigInt(0)
change line 258&367:
let y = BigInt("0x" + s.tostring("hex")); => let y = BigInt(s.tostring("hex"), 16);

However, when the test script was executed, the actual result did not match the expected result.

not ok 9 should be strictly equal
  ---
    operator: equal
    expected: '869304086633418279'
    actual:   '750918814058654607'
    at: Test.<anonymous> (/GitHub/node-fpe/test/FF3CipherTest.js:50:5)
    stack: |-
      Error: should be strictly equal

I tried to modify some other places, but the problem could not be solved. Could you please help to fix the problem?

Thanks!