@bsv/sdk
Version:
BSV Blockchain Software Development Kit
92 lines • 3.13 kB
JavaScript
import { SHA256HMAC } from './Hash.js';
import { toHex, toArray } from './utils.js';
/**
* This class behaves as a HMAC-based deterministic random bit generator (DRBG). It implements a deterministic random number generator using SHA256HMAC HASH function. It takes an initial entropy and nonce when instantiated for seeding purpose.
* @class DRBG
*
* @constructor
* @param entropy - Initial entropy either in number array or hexadecimal string.
* @param nonce - Initial nonce either in number array or hexadecimal string.
*
* @throws Throws an error message 'Not enough entropy. Minimum is 256 bits' when entropy's length is less than 32.
*
* @example
* const drbg = new DRBG('af12de...', '123ef...');
*/
export default class DRBG {
K;
V;
constructor(entropy, nonce) {
entropy = toArray(entropy, 'hex');
nonce = toArray(nonce, 'hex');
if (entropy.length < 32) {
throw new Error('Not enough entropy. Minimum is 256 bits');
}
const seed = entropy.concat(nonce);
this.K = new Array(32);
this.V = new Array(32);
for (let i = 0; i < 32; i++) {
this.K[i] = 0x00;
this.V[i] = 0x01;
}
this.update(seed);
}
/**
* Generates HMAC using the K value of the instance. This method is used internally for operations.
*
* @method hmac
* @returns The SHA256HMAC object created with K value.
*
* @example
* const hmac = drbg.hmac();
*/
hmac() {
return new SHA256HMAC(this.K);
}
/**
* Updates the `K` and `V` values of the instance based on the seed.
* The seed if not provided uses `V` as seed.
*
* @method update
* @param seed - an optional value that used to update `K` and `V`. Default is `undefined`.
* @returns Nothing, but updates the internal state `K` and `V` value.
*
* @example
* drbg.update('e13af...');
*/
update(seed) {
let kmac = this.hmac().update(this.V).update([0x00]);
if (seed !== undefined) {
kmac = kmac.update(seed);
}
this.K = kmac.digest();
this.V = this.hmac().update(this.V).digest();
if (seed === undefined) {
return;
}
this.K = this.hmac().update(this.V).update([0x01]).update(seed).digest();
this.V = this.hmac().update(this.V).digest();
}
/**
* Generates deterministic random hexadecimal string of given length.
* In every generation process, it also updates the internal state `K` and `V`.
*
* @method generate
* @param len - The length of required random number.
* @returns The required deterministic random hexadecimal string.
*
* @example
* const randomHex = drbg.generate(256);
*/
generate(len) {
let temp = [];
while (temp.length < len) {
this.V = this.hmac().update(this.V).digest();
temp = temp.concat(this.V);
}
const res = temp.slice(0, len);
this.update();
return toHex(res);
}
}
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