/**

 * DER

 * 

 * A basic class to parse DER structures.

 * It is very incomplete, but sufficient to extract whatever data we need so far.

 * Copyright (c) 2007 Henri Torgemane

 * 

 * See LICENSE.txt for full license information.

 */

package com.hurlant.util.der

{

	import com.hurlant.math.BigInteger;

	

	import flash.utils.ByteArray;

	import com.hurlant.util.der.Sequence;

	import com.hurlant.util.Hex;

	

	// goal 1: to be able to parse an RSA Private Key PEM file.

	// goal 2: to parse an X509v3 cert. kinda.

	

	/**

	 * DER for dummies:

	 * http://luca.ntop.org/Teaching/Appunti/asn1.html

	 * 

	 * This class does the bare minimum to get by. if that.

	 */

	public class DER

	{

		public static var indent:String = "";

		

		public static function parse(der:ByteArray, structure:*=null):IAsn1Type {

/* 			if (der.position==0) {

				trace("DER.parse: "+Hex.fromArray(der));

			}

 */			// type

			var type:int = der.readUnsignedByte();

			var constructed:Boolean = (type&0x20)!=0;

			type &=0x1F;

			// length

			var len:int = der.readUnsignedByte();

			if (len>=0x80) {

				// long form of length

				var count:int = len & 0x7f;

				len = 0;

				while (count>0) {

					len = (len<<8) | der.readUnsignedByte();

					count--;

				}

			}

			// data

			var b:ByteArray

			switch (type) {

				case 0x00: // WHAT IS THIS THINGY? (seen as 0xa0)

					// (note to self: read a spec someday.)

					// for now, treat as a sequence.

				case 0x10: // SEQUENCE/SEQUENCE OF. whatever

					// treat as an array

					var p:int = der.position;

					var o:Sequence = new Sequence(type, len);

					var arrayStruct:Array = structure as Array;

					if (arrayStruct!=null) {

						// copy the array, as we destroy it later.

						arrayStruct = arrayStruct.concat();

					}

					while (der.position < p+len) {

						var tmpStruct:Object = null

						if (arrayStruct!=null) {

							tmpStruct = arrayStruct.shift();

						}

						if (tmpStruct!=null) {

							while (tmpStruct && tmpStruct.optional) {

								// make sure we have something that looks reasonable. XXX I'm winging it here..

								var wantConstructed:Boolean = (tmpStruct.value is Array);

								var isConstructed:Boolean = isConstructedType(der);

								if (wantConstructed!=isConstructed) {

									// not found. put default stuff, or null

									o.push(tmpStruct.defaultValue);

									o[tmpStruct.name] = tmpStruct.defaultValue;

									// try the next thing

									tmpStruct = arrayStruct.shift();

								} else {

									break;

								}

							}

						}

						if (tmpStruct!=null) {

							var name:String = tmpStruct.name;

							var value:* = tmpStruct.value;

							if (tmpStruct.extract) {

								// we need to keep a binary copy of this element

								var size:int = getLengthOfNextElement(der);

								var ba:ByteArray = new ByteArray;

								ba.writeBytes(der, der.position, size);

								o[name+"_bin"] = ba;

							}

							var obj:IAsn1Type = DER.parse(der, value);

							o.push(obj);

							o[name] = obj;

						} else {

							o.push(DER.parse(der));

						}

					}

					return o;

				case 0x11: // SET/SET OF

					p = der.position;

					var s:Set = new Set(type, len);

					while (der.position < p+len) {

						s.push(DER.parse(der));

					}

					return s;

				case 0x02: // INTEGER

					// put in a BigInteger

					b = new ByteArray;

					der.readBytes(b,0,len);

					b.position=0;

					return new Integer(type, len, b);

				case 0x06: // OBJECT IDENTIFIER:

					b = new ByteArray;

					der.readBytes(b,0,len);

					b.position=0;

					return new ObjectIdentifier(type, len, b);

				default:

					trace("I DONT KNOW HOW TO HANDLE DER stuff of TYPE "+type);

					// fall through

				case 0x03: // BIT STRING

					if (der[der.position]==0) {

						//trace("Horrible Bit String pre-padding removal hack."); // I wish I had the patience to find a spec for this.

						der.position++;

						len--;

					}

				case 0x04: // OCTET STRING

					// stuff in a ByteArray for now.

					var bs:ByteString = new ByteString(type, len);

					der.readBytes(bs,0,len);

					return bs;

				case 0x05: // NULL

					// if len!=0, something's horribly wrong.

					// should I check?

					return null;

				case 0x13: // PrintableString

					var ps:PrintableString = new PrintableString(type, len);

					ps.setString(der.readMultiByte(len, "US-ASCII"));

					return ps;

				case 0x22: // XXX look up what this is. openssl uses this to store my email.

				case 0x14: // T61String - an horrible format we don't even pretend to support correctly

					ps = new PrintableString(type, len);

					ps.setString(der.readMultiByte(len, "latin1"));

					return ps;

				case 0x17: // UTCTime

					var ut:UTCTime = new UTCTime(type, len);

					ut.setUTCTime(der.readMultiByte(len, "US-ASCII"));

					return ut;

			}

		}

		

		private static function getLengthOfNextElement(b:ByteArray):int {

			var p:uint = b.position;

			// length

			b.position++;

			var len:int = b.readUnsignedByte();

			if (len>=0x80) {

				// long form of length

				var count:int = len & 0x7f;

				len = 0;

				while (count>0) {

					len = (len<<8) | b.readUnsignedByte();

					count--;

				}

			}

			len += b.position-p; // length of length

			b.position = p;

			return len;

		}

		private static function isConstructedType(b:ByteArray):Boolean {

			var type:int = b[b.position];

			return (type&0x20)!=0;

		}

		

		public static function wrapDER(type:int, data:ByteArray):ByteArray {

			var d:ByteArray = new ByteArray;

			d.writeByte(type);

			var len:int = data.length;

			if (len<128) {

				d.writeByte(len);

			} else if (len<256) {

				d.writeByte(1 | 0x80);

				d.writeByte(len);

			} else if (len<65536) {

				d.writeByte(2 | 0x80);

				d.writeByte(len>>8);

				d.writeByte(len);

			} else if (len<65536*256) {

				d.writeByte(3 | 0x80);

				d.writeByte(len>>16);

				d.writeByte(len>>8);

				d.writeByte(len);

			} else {

				d.writeByte(4 | 0x80);

				d.writeByte(len>>24);

				d.writeByte(len>>16);

				d.writeByte(len>>8);

				d.writeByte(len);

			}

			d.writeBytes(data);

			d.position=0;

			return d;

			

		}

	}

}