1package main
2 
3import (
4	"crypto/hmac"
5	"crypto/sha256"
6	"encoding/hex"
7	"fmt"
8	"math/bits"
9	"net/http"
10	"strconv"
11	"strings"
12)
13 
14// VerifyPoW verifies client proof in O(1) time
15func VerifyPoW(secretKey, token string, nonce int64, context string) (bool, error) {
16	parts := strings.Split(token, ".")
17	if len(parts) != 2 {
18		return false, fmt.Errorf("invalid token format")
19	}
20	payloadB64, sig := parts[0], parts[1]
21 
22	// 1. Verify HMAC-SHA256 signature
23	mac := hmac.New(sha256.New, []byte(secretKey))
24	mac.Write([]byte(payloadB64))
25	expectedSig := hex.EncodeToString(mac.Sum(nil))
26	if !hmac.Equal([]byte(sig), []byte(expectedSig)) {
27		return false, fmt.Errorf("signature mismatch")
28	}
29 
30	// 2. Count leading zero bits of candidate hash
31	candidate := fmt.Sprintf("salt:%d:%s", nonce, context)
32	h := sha256.Sum256([]byte(candidate))
33	
34	var zeroBits int
35	for _, b := range h {
36		if b == 0 {
37			zeroBits += 8
38		} else {
39			zeroBits += bits.LeadingZeros8(b)
40			break
41		}
42	}
43	return zeroBits >= 16, nil
44}

1// Background Web Worker PoW Solver (worker.js)
2self.onmessage = async (e) => {
3  const { salt, context, difficulty } = e.data;
4  const encoder = new TextEncoder();
5  let nonce = 0;
6  
7  while (true) {
8    const candidate = `${salt}:${nonce}:${context}`;
9    const buf = await crypto.subtle.digest("SHA-256", encoder.encode(candidate));
10    const bytes = new Uint8Array(buf);
11    
12    // Count leading zero bits
13    let zeroBits = 0;
14    for (let i = 0; i < bytes.length; i++) {
15      if (bytes[i] === 0) zeroBits += 8;
16      else { zeroBits += Math.clz32(bytes[i]) - 24; break; }
17    }
18    
19    if (zeroBits >= difficulty) {
20      self.postMessage({ solved: true, nonce });
21      return;
22    }
23    nonce++;
24  }
25};

1import hashlib, hmac
2 
3def verify_pow(secret_key: str, token: str, nonce: int, context: str) -> bool:
4    parts = token.split(".")
5    if len(parts) != 2:
6        return False
7    payload_b64, signature = parts
8    
9    # 1. Verify HMAC
10    expected = hmac.new(secret_key.encode(), payload_b64.encode(), hashlib.sha256).hexdigest()
11    if not hmac.compare_digest(signature, expected):
12        return False
13        
14    # 2. Check hash difficulty
15    candidate = f"salt:{nonce}:{context}".encode()
16    digest = hashlib.sha256(candidate).digest()
17    
18    zero_bits = 0
19    for byte in digest:
20        if byte == 0:
21            zero_bits += 8
22        else:
23            zero_bits += (8 - byte.bit_length())
24            break
25            
26    return zero_bits >= 16

1<?php
2function verify_pow($secret_key, $token, $nonce, $context) {
3    $parts = explode(".", $token);
4    if (count($parts) !== 2) return false;
5    list($payload_b64, $signature) = $parts;
6 
7    // 1. Verify HMAC
8    $expected = hash_hmac("sha256", $payload_b64, $secret_key);
9    if (!hash_equals($signature, $expected)) return false;
10 
11    // 2. Check hash candidate
12    $candidate = "salt:" . $nonce . ":" . $context;
13    $raw_hash = hash("sha256", $candidate, true);
14 
15    $zero_bits = 0;
16    for ($i = 0; $i < strlen($raw_hash); $i++) {
17        $byte = ord($raw_hash[$i]);
18        if ($byte === 0) {
19            $zero_bits += 8;
20        } else {
21            $zero_bits += (8 - strlen(decbin($byte)));
22            break;
23        }
24    }
25    return $zero_bits >= 16;
26}

1#!/bin/sh
2# POSIX-compliant PoW solver
3SALT="a1b2c3d4e5f67890"
4CTX="job_context_fingerprint"
5 
6nonce=0
7while :; do
8    hash=$(printf "%s:%s:%s" "$SALT" "$nonce" "$CTX" | sha256sum | awk "{print \$1}")
9    case "$hash" in
10        0000*)
11            printf "Solved! Nonce: %s Hash: %s\n" "$nonce" "$hash"
12            break
13            ;;
14    esac
15    nonce=$((nonce + 1))
16done