demo & proof of concept

2025-03-15 08:38:55 +00:00 · 2024-08-15 22:48:04 +02:00 · 2024-08-15 22:48:04 +02:00 · 44f96fffe9
commit 44f96fffe9
2 changed files with 159 additions and 0 deletions
--- a/index.html
+++ b/index.html
@ -0,0 +1,106 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <script src="main.js"></script>
+  <style>
+    .captcha {
+      width: 300px;
+      height: 70px;
+      padding: 20px;
+      border: 1px solid grey;
+      box-sizing: border-box;
+      font-size: 20px;
+      font-family: sans-serif;
+    }
+    
+    .captcha span {
+      position: relative;
+      top: -9px;
+    }
+    
+    .captcha .checkbox {
+      position: relative;
+      margin: 0;
+      margin-right: 20px;
+      height: 30px;
+      width: 30px;
+      display: inline-block;
+      background-color: white;
+      cursor: pointer;
+      border: 1px solid black;
+      border-radius: 3px;
+    }
+    
+    .captcha .checkbox:hover {
+      background-color: lightgrey;
+    }
+    
+    .captcha .checkbox.checked {
+      background-color: #2196F3;
+    }
+    
+    .captcha .checkbox.checked::before {
+      position: absolute;
+      display: block;
+      content: "";
+      width: 7px;
+      height: 15px;
+      top: 2px;
+      left: 9px;
+      border: white solid;
+      border-width: 0 5px 5px 0;
+      transform: rotate(45deg);
+    }
+    
+    .captcha .checkbox.loading {
+    }
+    
+    .captcha .checkbox.loading::before {
+      content: "";
+      display: block;
+      position: absolute;
+      top: 2.5px;
+      left: 2.5px;
+      width: 17px;
+      height: 17px;
+      border: 4px solid;
+      border-radius: 50%;
+      border-color: black transparent black transparent;
+      animation: captchaLoading infinite 1s;
+    }
+    
+    @keyframes captchaLoading {
+      to{
+        transform: rotate(.5turn)
+      }
+    }
+
+    
+  </style>
+  <script>
+    window.addEventListener("load", () => {
+      [...document.querySelectorAll(".captcha .checkbox")].forEach(c => c.addEventListener("click", async function() {
+        const result = document.getElementById("result");
+        result.innerText = "Calculating..."; 
+      
+        this.classList.add("loading");
+        
+        const challenge = makeSuffix(Math.floor(Math.random() * Number.MAX_SAFE_INTEGER)) + ":" + makeSuffix(new Date().valueOf()) + ":";
+        
+        const response = await findHashWithPrefix(15, challenge);
+        result.innerText = "Challenge Response: " + response;
+        
+        this.classList.remove("loading");
+        this.classList.add("checked");
+      }));
+    });
+  </script>
+</head>
+<body>
+  <div class="captcha">
+    <div class="checkbox"></div>
+    <span>I am not a robot.</span>
+  </div>
+  <div id="result"></div>
+</body>
+</html>
--- a/main.js
+++ b/main.js
@ -0,0 +1,53 @@
+const hexCharset = "0123456789abcdef".split("");
+const suffixCharset = [
+    "0123456789", 
+    "abcdefghijklmnopqrstuvwxyz",
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZ", 
+    "+-",
+].flatMap(set => set.split(""));
+const suffixCharsetBits = 6;
+
+const sha256 = "SHA-256";
+
+Uint8Array.prototype.toHex = function() {
+    return [...this].map(c => hexCharset[c >> 4] + hexCharset[c & 15]).join("");
+};
+
+Uint8Array.prototype.hasPrefix = function(array, bits) {
+    for(let i = 0; i < array.length && i * 8 < bits; i++) {
+        const bitsForByte = Math.min(8, bits - i * 8);
+        const bitMask = ((1 << bitsForByte) - 1) << (8 - bitsForByte);
+        
+        if ((this[i] & bitMask) != (array[i] & bitMask)) {
+            return false;
+        }
+    }
+    return true;
+};
+
+async function digest(algo, input) {
+    return new Uint8Array(await crypto.subtle.digest(algo, new TextEncoder().encode(input)));
+}
+
+function makeSuffix(index) {
+    let result = "";
+    
+    while (index > 0) {
+        result += suffixCharset[index & ((1 << suffixCharsetBits) - 1)];
+        index >>= suffixCharsetBits;
+    }
+    
+    return result;
+}
+
+async function findHashWithPrefix(hashPrefixBits, inputPrefix) {
+    const hashPrefix = new Uint8Array(Array(Math.ceil(hashPrefixBits / 8)).map(c => 0));
+    let iteration = 0;
+    
+    do {
+        var message = inputPrefix + makeSuffix(iteration++)
+        var hash = await digest(sha256, message);
+    } while (!hash.hasPrefix(hashPrefix, hashPrefixBits));
+    
+    return message;
+}