WIP JWK-to-PEM

lib/asn1.js

@@ -1,8 +1,80 @@
 'use strict';
 
-var ASN1 = module.exports = function ASN1() {
+//
+// A dumbed-down, minimal ASN.1 parser / packer combo
+//
+// Note: generally I like to write congruent code
+// (i.e. output can be used as input and vice-versa)
+// However, this seemed to be more readable and easier
+// to use written as-is, asymmetrically.
+// (I also generally prefer to export objects rather
+// functions but, yet again, asthetics one in this case)
+
+var Enc = require('./encoding.js');
+
+//
+// Packer
+//
+
+// Almost every ASN.1 type that's important for CSR
+// can be represented generically with only a few rules.
+var ASN1 = module.exports = function ASN1(/*type, hexstrings...*/) {
+  var args = Array.prototype.slice.call(arguments);
+  var typ = args.shift();
+  var str = args.join('').replace(/\s+/g, '').toLowerCase();
+  var len = (str.length/2);
+  var lenlen = 0;
+  var hex = typ;
+
+  // We can't have an odd number of hex chars
+  if (len !== Math.round(len)) {
+    throw new Error("invalid hex");
+  }
+
+  // The first byte of any ASN.1 sequence is the type (Sequence, Integer, etc)
+  // The second byte is either the size of the value, or the size of its size
+
+  // 1. If the second byte is < 0x80 (128) it is considered the size
+  // 2. If it is > 0x80 then it describes the number of bytes of the size
+  //    ex: 0x82 means the next 2 bytes describe the size of the value
+  // 3. The special case of exactly 0x80 is "indefinite" length (to end-of-file)
+
+  if (len > 127) {
+    lenlen += 1;
+    while (len > 255) {
+      lenlen += 1;
+      len = len >> 8;
+    }
+  }
+
+  if (lenlen) { hex += Enc.numToHex(0x80 + lenlen); }
+  return hex + Enc.numToHex(str.length/2) + str;
 };
 
+// The Integer type has some special rules
+ASN1.UInt = function UINT() {
+  var str = Array.prototype.slice.call(arguments).join('');
+  var first = parseInt(str.slice(0, 2), 16);
+
+  // If the first byte is 0x80 or greater, the number is considered negative
+  // Therefore we add a '00' prefix if the 0x80 bit is set
+  if (0x80 & first) { str = '00' + str; }
+
+  return ASN1('02', str);
+};
+
+// The Bit String type also has a special rule
+ASN1.BitStr = function BITSTR() {
+  var str = Array.prototype.slice.call(arguments).join('');
+  // '00' is a mask of how many bits of the next byte to ignore
+  return ASN1('03', '00' + str);
+};
+
+
+//
+// Parser
+//
+
 ASN1.ELOOP = "uASN1.js Error: iterated over 15+ elements (probably a malformed file)";
 ASN1.EDEEP = "uASN1.js Error: element nested 10+ layers deep (probably a malformed file)";
 // Container Types are Sequence 0x30, Octect String 0x04, Array? (0xA0, 0xA1)

lib/encoding.js

@@ -15,6 +15,14 @@ Enc.bufToHex = function toHex(u8) {
   return hex.join('').toLowerCase();
 };
 
+Enc.numToHex = function numToHex(d) {
+  d = d.toString(16);
+  if (d.length % 2) {
+    return '0' + d;
+  }
+  return d;
+};
+
 Enc.bufToBase64 = function toHex(u8) {
   // we want to maintain api compatability with browser APIs,
   // so we assume that this could be a Uint8Array