acme.js/asn1/packer.js

'use strict';

var ASN1 = module.exports;
var Enc = require('@root/encoding/hex');

//
// Packer
//

// Almost every ASN.1 type that's important for CSR
// can be represented generically with only a few rules.
function Any(/*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;
}
ASN1.Any = Any;

// 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 Any('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 Any('03', '00' + str);
};

ASN1.pack = function(arr) {
	var typ = Enc.numToHex(arr[0]);
	var str = '';
	if (Array.isArray(arr[1])) {
		arr[1].forEach(function(a) {
			str += ASN1.pack(a);
		});
	} else if ('string' === typeof arr[1]) {
		str = arr[1];
	} else {
		throw new Error('unexpected array');
	}
	if ('03' === typ) {
		return ASN1.BitStr(str);
	} else if ('02' === typ) {
		return ASN1.UInt(str);
	} else {
		return Any(typ, str);
	}
};