Issue 4465 - Move rsa module from adblockpluschrome

lib/rsa.js

Index: lib/rsa.js
diff --git a/lib/rsa.js b/lib/rsa.js
new file mode 100644
index 0000000000000000000000000000000000000000..6c6638cb266a491b0813a3169534c61f4aba9d48
--- /dev/null
+++ b/lib/rsa.js
@@ -0,0 +1,191 @@
+/*
+ * This file is part of Adblock Plus <https://adblockplus.org/>,
+ * Copyright (C) 2006-2016 Eyeo GmbH
+ *
+ * Adblock Plus is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * Adblock Plus is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * This is a specialized RSA library meant only to verify SHA1-based signatures.
+ */
+
+let {BigInteger} = require("jsbn");
+let Rusha = require("rusha");
+
+let rusha = new Rusha();
+
+// Define ASN.1 templates for the data structures used
+function seq()
+{
+  return {type: 0x30, children: Array.prototype.slice.call(arguments)};
+}
+function obj(id)
+{
+  return {type: 0x06, content: id};
+}
+function bitStr(contents)
+{
+  return {type: 0x03, encapsulates: contents};
+}
+function intResult(id)
+{
+  return {type: 0x02, out: id};
+}
+function octetResult(id)
+{
+  return {type: 0x04, out: id};
+}
+
+// See http://www.cryptopp.com/wiki/Keys_and_Formats#RSA_PublicKey
+// 2A 86 48 86 F7 0D 01 01 01 means 1.2.840.113549.1.1.1
+var publicKeyTemplate = seq(seq(obj("\x2A\x86\x48\x86\xF7\x0D\x01\x01\x01"), {}), bitStr(seq(intResult("n"), intResult("e"))));
+
+// See http://tools.ietf.org/html/rfc3447#section-9.2 step 2
+// 2B 0E 03 02 1A means 1.3.14.3.2.26
+var signatureTemplate = seq(seq(obj("\x2B\x0E\x03\x02\x1A"), {}), octetResult("sha1"));
+
+/**
+ * Reads ASN.1 data matching the template passed in. This will throw an
+ * exception if the data format doesn't match the template. On success an
+ * object containing result properties is returned.
+ *
+ * See http://luca.ntop.org/Teaching/Appunti/asn1.html for info on the format.
+ */
+function readASN1(data, templ)
+{
+  var pos = 0;
+  function next()
+  {
+    return data.charCodeAt(pos++);
+  }
+
+  function readLength()
+  {
+    var len = next();
+    if (len & 0x80)
+    {
+      var cnt = len & 0x7F;
+      if (cnt > 2 || cnt == 0)
+        throw "Unsupported length";
+
+      len = 0;
+      for (var i = 0; i < cnt; i++)
+        len += next() << (cnt - 1 - i) * 8;
+      return len;
+    }
+    else
+      return len;
+  }
+
+  function readNode(curTempl)
+  {
+    var type = next();
+    var len = readLength();
+    if ("type" in curTempl && curTempl.type != type)
+      throw "Unexpected type";
+    if ("content" in curTempl && curTempl.content != data.substr(pos, len))
+      throw "Unexpected content";
+    if ("out" in curTempl)
+      out[curTempl.out] = new BigInteger(data.substr(pos, len), 256);
+    if ("children" in curTempl)
+    {
+      var i, end;
+      for (i = 0, end = pos + len; pos < end; i++)
+      {
+        if (i >= curTempl.children.length)
+          throw "Too many children";
+        readNode(curTempl.children[i]);
+      }
+      if (i < curTempl.children.length)
+        throw "Too few children";
+      if (pos > end)
+        throw "Children too large";
+    }
+    else if ("encapsulates" in curTempl)
+    {
+      if (next() != 0)
+        throw "Encapsulation expected";
+      readNode(curTempl.encapsulates);
+    }
+    else
+      pos += len;
+  }
+
+  var out = {};
+  readNode(templ);
+  if (pos != data.length)
+    throw "Too much data";
+  return out;
+}
+
+/**
+ * Reads a BER-encoded RSA public key. On success returns an object with the
+ * properties n and e (the components of the key), otherwise null.
+ */
+function readPublicKey(key)
+{
+  try
+  {
+    return readASN1(atob(key), publicKeyTemplate);
+  }
+  catch (e)
+  {
+    console.log("Invalid RSA public key: " + e);
+    return null;
+  }
+}
+
+/**
+ * Checks whether the signature is valid for the given public key and data.
+ */
+function verifySignature(key, signature, data)
+{
+  var keyData = readPublicKey(key);
+  if (!keyData)
+    return false;
+
+  // We need the exponent as regular number
+  keyData.e = parseInt(keyData.e.toString(16), 16);
+
+  // Decrypt signature data using RSA algorithm
+  var sigInt = new BigInteger(atob(signature), 256);
+  var digest = sigInt.modPowInt(keyData.e, keyData.n).toString(256);
+
+  try
+  {
+    var pos = 0;
+    function next()
+    {
+      return digest.charCodeAt(pos++);
+    }
+
+    // Skip padding, see http://tools.ietf.org/html/rfc3447#section-9.2 step 5
+    if (next() != 1)
+      throw "Wrong padding in signature digest";
+    while (next() == 255) {}
+    if (digest.charCodeAt(pos - 1) != 0)
+      throw "Wrong padding in signature digest";
+
+    // Rest is an ASN.1 structure, get the SHA1 hash from it and compare to
+    // the real one
+    var sha1 = readASN1(digest.substr(pos), signatureTemplate).sha1;
+    var expected = new BigInteger(rusha.digest(data), 16);
+    return (sha1.compareTo(expected) == 0);
+  }
+  catch (e)
+  {
+    console.log("Invalid encrypted signature: " + e);
+    return false;
+  }
+}
+exports.verifySignature = verifySignature;