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# Bluecrypt ASN.1 Parser
An ASN.1 parser in less than 100 lines of Vanilla JavaScript,
An ASN.1 decoder in less than 100 lines of Vanilla JavaScript,
part of the Bluecrypt suite.
<br>
<small>(< 150 with newlines and comments)</small>
@ -17,6 +17,10 @@ part of the Bluecrypt suite.
* [x] Online [Demo](https://coolaj86.com/demos/asn1-parser/)
* [ ] Node.js (built, publishing soon)
### Need an ASN.1 Builder too?
Check out https://git.coolaj86.com/coolaj86/asn1-packer.js/
# Demo
<https://coolaj86.com/demos/asn1-parser/>

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// Copyright 2018 AJ ONeal. All rights reserved
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
;(function (exports) {
'use strict';
@ -13,87 +17,102 @@ var PEM = exports.PEM;
// Parser
//
ASN1.ELOOP = "uASN1.js Error: iterated over 15+ elements (probably a malformed file)";
ASN1.EDEEP = "uASN1.js Error: element nested 20+ layers deep (probably a malformed file)";
// Although I've only seen 9 max in https certificates themselves,
// but each domain list could have up to 100
ASN1.ELOOPN = 102;
ASN1.ELOOP = "uASN1.js Error: iterated over " + ASN1.ELOOPN + "+ elements (probably a malformed file)";
// I've seen https certificates go 29 deep
ASN1.EDEEPN = 60;
ASN1.EDEEP = "uASN1.js Error: element nested " + ASN1.EDEEPN + "+ layers deep (probably a malformed file)";
// Container Types are Sequence 0x30, Container Array? (0xA0, 0xA1)
// Value Types are Integer 0x02, Null 0x05, Object ID 0x06, Value Array? (0x82)
// Value Types are Boolean 0x01, Integer 0x02, Null 0x05, Object ID 0x06, String 0x0C, 0x16, 0x13, 0x1e Value Array? (0x82)
// Bit String (0x03) and Octet String (0x04) may be values or containers
// Sometimes Bit String is used as a container (RSA Pub Spki)
ASN1.CTYPES = [ 0x30, 0x31, 0xa0, 0xa1 ];
ASN1.VTYPES = [ 0x02, 0x05, 0x06, 0x82 ];
ASN1.parse = function parseAsn1(buf, depth, ws) {
if (!ws) { ws = ''; }
if (!depth) { depth = 0; }
if (depth >= 20) { throw new Error(ASN1.EDEEP); }
ASN1.VTYPES = [ 0x01, 0x02, 0x05, 0x06, 0x0c, 0x82 ];
ASN1.parse = function parseAsn1Helper(buf) {
//var ws = ' ';
function parseAsn1(buf, depth, eager) {
if (depth.length >= ASN1.EDEEPN) { throw new Error(ASN1.EDEEP); }
var index = 2; // we know, at minimum, data starts after type (0) and lengthSize (1)
var asn1 = { type: buf[0], lengthSize: 0, length: buf[1] };
var child;
var iters = 0;
var adjust = 0;
var adjustedLen;
var index = 2; // we know, at minimum, data starts after type (0) and lengthSize (1)
var asn1 = { type: buf[0], lengthSize: 0, length: buf[1] };
var child;
var iters = 0;
var adjust = 0;
var adjustedLen;
// Determine how many bytes the length uses, and what it is
if (0x80 & asn1.length) {
asn1.lengthSize = 0x7f & asn1.length;
// I think that buf->hex->int solves the problem of Endianness... not sure
asn1.length = parseInt(Enc.bufToHex(buf.slice(index, index + asn1.lengthSize)), 16);
index += asn1.lengthSize;
}
// High-order bit Integers have a leading 0x00 to signify that they are positive.
// Bit Streams use the first byte to signify padding, which x.509 doesn't use.
if (0x00 === buf[index] && (0x02 === asn1.type || 0x03 === asn1.type)) {
// However, 0x00 on its own is a valid number
if (asn1.length > 1) {
index += 1;
adjust = -1;
// Determine how many bytes the length uses, and what it is
if (0x80 & asn1.length) {
asn1.lengthSize = 0x7f & asn1.length;
// I think that buf->hex->int solves the problem of Endianness... not sure
asn1.length = parseInt(Enc.bufToHex(buf.slice(index, index + asn1.lengthSize)), 16);
index += asn1.lengthSize;
}
}
adjustedLen = asn1.length + adjust;
//console.warn(ws + '0x' + Enc.numToHex(asn1.type), index, 'len:', asn1.length, asn1);
function parseChildren(eager) {
asn1.children = [];
//console.warn('1 len:', (2 + asn1.lengthSize + asn1.length), 'idx:', index, 'clen:', 0);
while (iters < 15 && index < (2 + asn1.length + asn1.lengthSize)) {
iters += 1;
child = ASN1.parse(buf.slice(index, index + adjustedLen), (depth || 0) + 1, ws + ' ');
// The numbers don't match up exactly and I don't remember why...
// probably something with adjustedLen or some such, but the tests pass
index += (2 + child.lengthSize + child.length);
//console.warn('2 len:', (2 + asn1.lengthSize + asn1.length), 'idx:', index, 'clen:', (2 + child.lengthSize + child.length));
if (index > (2 + asn1.lengthSize + asn1.length)) {
if (!eager) { console.error(JSON.stringify(asn1, ASN1._replacer, 2)); }
throw new Error("Parse error: child value length (" + child.length
+ ") is greater than remaining parent length (" + (asn1.length - index)
+ " = " + asn1.length + " - " + index + ")");
// High-order bit Integers have a leading 0x00 to signify that they are positive.
// Bit Streams use the first byte to signify padding, which x.509 doesn't use.
if (0x00 === buf[index] && (0x02 === asn1.type || 0x03 === asn1.type)) {
// However, 0x00 on its own is a valid number
if (asn1.length > 1) {
index += 1;
adjust = -1;
}
asn1.children.push(child);
//console.warn(ws + '0x' + Enc.numToHex(asn1.type), index, 'len:', asn1.length, asn1);
}
if (index !== (2 + asn1.lengthSize + asn1.length)) {
//console.warn('index:', index, 'length:', (2 + asn1.lengthSize + asn1.length));
throw new Error("premature end-of-file");
}
if (iters >= 15) { throw new Error(ASN1.ELOOP); }
adjustedLen = asn1.length + adjust;
delete asn1.value;
return asn1;
//console.warn(depth.join(ws) + '0x' + Enc.numToHex(asn1.type), index, 'len:', asn1.length, asn1);
function parseChildren(eager) {
asn1.children = [];
//console.warn('1 len:', (2 + asn1.lengthSize + asn1.length), 'idx:', index, 'clen:', 0);
while (iters < ASN1.ELOOPN && index < (2 + asn1.length + asn1.lengthSize)) {
iters += 1;
depth.length += 1;
child = parseAsn1(buf.slice(index, index + adjustedLen), depth, eager);
depth.length -= 1;
// The numbers don't match up exactly and I don't remember why...
// probably something with adjustedLen or some such, but the tests pass
index += (2 + child.lengthSize + child.length);
//console.warn('2 len:', (2 + asn1.lengthSize + asn1.length), 'idx:', index, 'clen:', (2 + child.lengthSize + child.length));
if (index > (2 + asn1.lengthSize + asn1.length)) {
if (!eager) { console.error(JSON.stringify(asn1, ASN1._replacer, 2)); }
throw new Error("Parse error: child value length (" + child.length
+ ") is greater than remaining parent length (" + (asn1.length - index)
+ " = " + asn1.length + " - " + index + ")");
}
asn1.children.push(child);
//console.warn(depth.join(ws) + '0x' + Enc.numToHex(asn1.type), index, 'len:', asn1.length, asn1);
}
if (index !== (2 + asn1.lengthSize + asn1.length)) {
//console.warn('index:', index, 'length:', (2 + asn1.lengthSize + asn1.length));
throw new Error("premature end-of-file");
}
if (iters >= ASN1.ELOOPN) { throw new Error(ASN1.ELOOP); }
delete asn1.value;
return asn1;
}
// Recurse into types that are _always_ containers
if (-1 !== ASN1.CTYPES.indexOf(asn1.type)) { return parseChildren(eager); }
// Return types that are _always_ values
asn1.value = buf.slice(index, index + adjustedLen);
if (-1 !== ASN1.VTYPES.indexOf(asn1.type)) { return asn1; }
// For ambigious / unknown types, recurse and return on failure
// (and return child array size to zero)
try { return parseChildren(true); }
catch(e) { asn1.children.length = 0; return asn1; }
}
// Recurse into types that are _always_ containers
if (-1 !== ASN1.CTYPES.indexOf(asn1.type)) { return parseChildren(); }
// Return types that are _always_ values
asn1.value = buf.slice(index, index + adjustedLen);
if (-1 !== ASN1.VTYPES.indexOf(asn1.type)) { return asn1; }
// For ambigious / unknown types, recurse and return on failure
// (and return child array size to zero)
try { return parseChildren(true); }
catch(e) { asn1.children.length = 0; return asn1; }
var asn1 = parseAsn1(buf, []);
var len = buf.byteLength || buf.length;
if (len !== 2 + asn1.lengthSize + asn1.length) {
throw new Error("Length of buffer does not match length of ASN.1 sequence.");
}
return asn1;
};
ASN1._replacer = function (k, v) {
if ('type' === k) { return '0x' + Enc.numToHex(v); }

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<body>
<h1>Bluecrypt ASN.1 Parser</h1>
<h2>PEM (base64-encoded DER)</h2>
<textarea class="js-input" placeholder="Paste a PEM here">-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEIT1SWLxsacPiE5Z16jkopAn8/+85
rMjgyCokrnjDft6Y/YnA4A50yZe7CnFsqeDcpnPbubP6cpYiVcnevNIYyg==
-----END PUBLIC KEY-----</textarea>
<h2>Hex</h2>
<pre><code class="js-hex"> </code></pre>
<h2>ASN.1 Array</h2>
<pre><code class="js-array"> </code></pre>
<h2>ASN.1 Object</h2>
<pre><code class="js-json"> </code></pre>
<br>
<p>Made with <a href="https://git.coolaj86.com/coolaj86/asn1-parser/">asn1-parser.js</a></p>
<p>Made with <a href="https://git.coolaj86.com/coolaj86/asn1-parser.js/">asn1-parser.js</a></p>
<script src="./asn1-parser.js"></script>
<script>
var $input = document.querySelector('.js-input');
function toArray(next) {
console.log(next);
if (next.value) {
return [next.type, Enc.bufToHex(next.value)];
}
return [next.type, next.children.map(function (child) {
return toArray(child);
})];
}
function convert() {
console.log('keyup');
var pem = PEM.parseBlock(document.querySelector('.js-input').value);
var hex = Enc.bufToHex(pem.der);
document.querySelector('.js-hex').innerText = hex
.match(/.{2}/g).join(' ').match(/.{1,24}/g).join(' ').match(/.{1,50}/g).join('\n');
var json = ASN1.parse(pem.der);
var json;
try {
var pem = PEM.parseBlock(document.querySelector('.js-input').value);
var hex = Enc.bufToHex(pem.der);
var arr = [];
document.querySelector('.js-hex').innerText = hex
.match(/.{2}/g).join(' ').match(/.{1,24}/g).join(' ').match(/.{1,50}/g).join('\n');
json = ASN1.parse(pem.der);
} catch(e) {
json = { error: { message: e.message } };
}
document.querySelector('.js-json').innerText = JSON.stringify(json, ASN1._replacer, 2);
document.querySelector('.js-array').innerText = JSON.stringify(toArray(json), null, 2);
}
$input.addEventListener('keyup', convert);

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{
"name": "asn1-parser",
"version": "1.1.1",
"version": "1.1.8",
"description": "An ASN.1 parser in less than 100 lines of Vanilla JavaScript, part of the Bluecrypt suite.",
"homepage": "https://git.coolaj86.com/coolaj86/asn1-parser.js",
"main": "asn1-parser.js",
"scripts": {
"prepare": "uglifyjs asn1-parser.js > asn1-parser.min.js"
},
"directories": {
"lib": "lib"
},