Source Code Cross Referenced for RandomGUID.java in  » Project-Management » EmForce » ru » emdev » EmForge » util » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Project Management » EmForce » ru.emdev.EmForge.util 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        package ru.emdev.EmForge.util;
002:
003:        /*
004:         * RandomGUID
005:         * @version 1.2.1 11/05/02
006:         * @author Marc A. Mnich
007:         *
008:         * From www.JavaExchange.com, Open Software licensing
009:         *
010:         * 11/05/02 -- Performance enhancement from Mike Dubman.  
011:         *             Moved InetAddr.getLocal to static block.  Mike has measured
012:         *             a 10 fold improvement in run time.
013:         * 01/29/02 -- Bug fix: Improper seeding of nonsecure Random object
014:         *             caused duplicate GUIDs to be produced.  Random object
015:         *             is now only created once per JVM.
016:         * 01/19/02 -- Modified random seeding and added new constructor
017:         *             to allow secure random feature.
018:         * 01/14/02 -- Added random function seeding with JVM run time
019:         *
020:         */
021:
022:        import java.net.*;
023:        import java.util.*;
024:        import java.security.*;
025:
026:        /*
027:         * In the multitude of java GUID generators, I found none that
028:         * guaranteed randomness.  GUIDs are guaranteed to be globally unique
029:         * by using ethernet MACs, IP addresses, time elements, and sequential
030:         * numbers.  GUIDs are not expected to be random and most often are
031:         * easy/possible to guess given a sample from a given generator.
032:         * SQL Server, for example generates GUID that are unique but
033:         * sequencial within a given instance.
034:         *
035:         * GUIDs can be used as security devices to hide things such as
036:         * files within a filesystem where listings are unavailable (e.g. files
037:         * that are served up from a Web server with indexing turned off).
038:         * This may be desireable in cases where standard authentication is not
039:         * appropriate. In this scenario, the RandomGUIDs are used as directories.
040:         * Another example is the use of GUIDs for primary keys in a database
041:         * where you want to ensure that the keys are secret.  Random GUIDs can
042:         * then be used in a URL to prevent hackers (or users) from accessing
043:         * records by guessing or simply by incrementing sequential numbers.
044:         *
045:         * There are many other possiblities of using GUIDs in the realm of
046:         * security and encryption where the element of randomness is important.
047:         * This class was written for these purposes but can also be used as a
048:         * general purpose GUID generator as well.
049:         *
050:         * RandomGUID generates truly random GUIDs by using the system's
051:         * IP address (name/IP), system time in milliseconds (as an integer),
052:         * and a very large random number joined together in a single String
053:         * that is passed through an MD5 hash.  The IP address and system time
054:         * make the MD5 seed globally unique and the random number guarantees
055:         * that the generated GUIDs will have no discernable pattern and
056:         * cannot be guessed given any number of previously generated GUIDs.
057:         * It is generally not possible to access the seed information (IP, time,
058:         * random number) from the resulting GUIDs as the MD5 hash algorithm
059:         * provides one way encryption.
060:         *
061:         * ----> Security of RandomGUID: <-----
062:         * RandomGUID can be called one of two ways -- with the basic java Random
063:         * number generator or a cryptographically strong random generator
064:         * (SecureRandom).  The choice is offered because the secure random
065:         * generator takes about 3.5 times longer to generate its random numbers
066:         * and this performance hit may not be worth the added security
067:         * especially considering the basic generator is seeded with a
068:         * cryptographically strong random seed.
069:         *
070:         * Seeding the basic generator in this way effectively decouples
071:         * the random numbers from the time component making it virtually impossible
072:         * to predict the random number component even if one had absolute knowledge
073:         * of the System time.  Thanks to Ashutosh Narhari for the suggestion
074:         * of using the static method to prime the basic random generator.
075:         *
076:         * Using the secure random option, this class compies with the statistical
077:         * random number generator tests specified in FIPS 140-2, Security
078:         * Requirements for Cryptographic Modules, secition 4.9.1.
079:         *
080:         * I converted all the pieces of the seed to a String before handing
081:         * it over to the MD5 hash so that you could print it out to make
082:         * sure it contains the data you expect to see and to give a nice
083:         * warm fuzzy.  If you need better performance, you may want to stick
084:         * to byte[] arrays.
085:         *
086:         * I believe that it is important that the algorithm for
087:         * generating random GUIDs be open for inspection and modification.
088:         * This class is free for all uses.
089:         *
090:         *
091:         * - Marc
092:         */
093:
094:        public class RandomGUID extends Object {
095:
096:            public String valueBeforeMD5 = "";
097:            public String valueAfterMD5 = "";
098:            private static Random myRand;
099:            private static SecureRandom mySecureRand;
100:
101:            private static String s_id;
102:
103:            /*
104:             * Static block to take care of one time secureRandom seed.
105:             * It takes a few seconds to initialize SecureRandom.  You might
106:             * want to consider removing this static block or replacing
107:             * it with a "time since first loaded" seed to reduce this time.
108:             * This block will run only once per JVM instance.
109:             */
110:
111:            static {
112:                mySecureRand = new SecureRandom();
113:                long secureInitializer = mySecureRand.nextLong();
114:                myRand = new Random(secureInitializer);
115:                try {
116:                    s_id = InetAddress.getLocalHost().toString();
117:                } catch (UnknownHostException e) {
118:                    e.printStackTrace();
119:                }
120:
121:            }
122:
123:            /*
124:             * Default constructor.  With no specification of security option,
125:             * this constructor defaults to lower security, high performance.
126:             */
127:            public RandomGUID() {
128:                getRandomGUID(false);
129:            }
130:
131:            /*
132:             * Constructor with security option.  Setting secure true
133:             * enables each random number generated to be cryptographically
134:             * strong.  Secure false defaults to the standard Random function seeded
135:             * with a single cryptographically strong random number.
136:             */
137:            public RandomGUID(boolean secure) {
138:                getRandomGUID(secure);
139:            }
140:
141:            /*
142:             * Method to generate the random GUID
143:             */
144:            private void getRandomGUID(boolean secure) {
145:                MessageDigest md5 = null;
146:                StringBuffer sbValueBeforeMD5 = new StringBuffer();
147:
148:                try {
149:                    md5 = MessageDigest.getInstance("MD5");
150:                } catch (NoSuchAlgorithmException e) {
151:                    System.out.println("Error: " + e);
152:                }
153:
154:                try {
155:                    long time = System.currentTimeMillis();
156:                    long rand = 0;
157:
158:                    if (secure) {
159:                        rand = mySecureRand.nextLong();
160:                    } else {
161:                        rand = myRand.nextLong();
162:                    }
163:
164:                    // This StringBuffer can be a long as you need; the MD5
165:                    // hash will always return 128 bits.  You can change
166:                    // the seed to include anything you want here.
167:                    // You could even stream a file through the MD5 making
168:                    // the odds of guessing it at least as great as that
169:                    // of guessing the contents of the file!
170:                    sbValueBeforeMD5.append(s_id);
171:                    sbValueBeforeMD5.append(":");
172:                    sbValueBeforeMD5.append(Long.toString(time));
173:                    sbValueBeforeMD5.append(":");
174:                    sbValueBeforeMD5.append(Long.toString(rand));
175:
176:                    valueBeforeMD5 = sbValueBeforeMD5.toString();
177:                    md5.update(valueBeforeMD5.getBytes());
178:
179:                    byte[] array = md5.digest();
180:                    StringBuffer sb = new StringBuffer();
181:                    for (int j = 0; j < array.length; ++j) {
182:                        int b = array[j] & 0xFF;
183:                        if (b < 0x10)
184:                            sb.append('0');
185:                        sb.append(Integer.toHexString(b));
186:                    }
187:
188:                    valueAfterMD5 = sb.toString();
189:
190:                } catch (Exception e) {
191:                    System.out.println("Error:" + e);
192:                }
193:            }
194:
195:            /*
196:             * Convert to the standard format for GUID
197:             * (Useful for SQL Server UniqueIdentifiers, etc.)
198:             * Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6
199:             */
200:            public String toString() {
201:                String raw = valueAfterMD5.toUpperCase();
202:                StringBuffer sb = new StringBuffer();
203:                sb.append(raw.substring(0, 8));
204:                sb.append("-");
205:                sb.append(raw.substring(8, 12));
206:                sb.append("-");
207:                sb.append(raw.substring(12, 16));
208:                sb.append("-");
209:                sb.append(raw.substring(16, 20));
210:                sb.append("-");
211:                sb.append(raw.substring(20));
212:
213:                return sb.toString();
214:            }
215:
216:            /*
217:             * Demonstraton and self test of class
218:             */
219:            public static void main(String args[]) {
220:                for (int i = 0; i < 100; i++) {
221:                    RandomGUID myGUID = new RandomGUID();
222:                    System.out.println("Seeding String="
223:                            + myGUID.valueBeforeMD5);
224:                    System.out.println("rawGUID=" + myGUID.valueAfterMD5);
225:                    System.out.println("RandomGUID=" + myGUID.toString());
226:                }
227:            }
228:        }
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