Source for gnu.java.security.sig.rsa.EMSA_PSS

   1: /* EMSA_PSS.java --
   2:    Copyright (C) 2001, 2002, 2003, 2006 Free Software Foundation, Inc.
   3: 
   4: This file is a part of GNU Classpath.
   5: 
   6: GNU Classpath is free software; you can redistribute it and/or modify
   7: it under the terms of the GNU General Public License as published by
   8: the Free Software Foundation; either version 2 of the License, or (at
   9: your option) any later version.
  10: 
  11: GNU Classpath is distributed in the hope that it will be useful, but
  12: WITHOUT ANY WARRANTY; without even the implied warranty of
  13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14: General Public License for more details.
  15: 
  16: You should have received a copy of the GNU General Public License
  17: along with GNU Classpath; if not, write to the Free Software
  18: Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
  19: USA
  20: 
  21: Linking this library statically or dynamically with other modules is
  22: making a combined work based on this library.  Thus, the terms and
  23: conditions of the GNU General Public License cover the whole
  24: combination.
  25: 
  26: As a special exception, the copyright holders of this library give you
  27: permission to link this library with independent modules to produce an
  28: executable, regardless of the license terms of these independent
  29: modules, and to copy and distribute the resulting executable under
  30: terms of your choice, provided that you also meet, for each linked
  31: independent module, the terms and conditions of the license of that
  32: module.  An independent module is a module which is not derived from
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  34: this exception to your version of the library, but you are not
  35: obligated to do so.  If you do not wish to do so, delete this
  36: exception statement from your version.  */
  37: 
  38: 
  39: package gnu.java.security.sig.rsa;
  40: 
  41: import gnu.java.security.Configuration;
  42: import gnu.java.security.hash.HashFactory;
  43: import gnu.java.security.hash.IMessageDigest;
  44: import gnu.java.security.util.Util;
  45: 
  46: import java.util.Arrays;
  47: import java.util.logging.Logger;
  48: 
  49: /**
  50:  * An implementation of the EMSA-PSS encoding/decoding scheme.
  51:  * <p>
  52:  * EMSA-PSS coincides with EMSA4 in IEEE P1363a D5 except that EMSA-PSS acts on
  53:  * octet strings and not on bit strings. In particular, the bit lengths of the
  54:  * hash and the salt must be multiples of 8 in EMSA-PSS. Moreover, EMSA4 outputs
  55:  * an integer of a desired bit length rather than an octet string.
  56:  * <p>
  57:  * EMSA-PSS is parameterized by the choice of hash function Hash and mask
  58:  * generation function MGF. In this submission, MGF is based on a Hash
  59:  * definition that coincides with the corresponding definitions in IEEE Std
  60:  * 1363-2000, PKCS #1 v2.0, and the draft ANSI X9.44. In PKCS #1 v2.0 and the
  61:  * draft ANSI X9.44, the recommended hash function is SHA-1, while IEEE Std
  62:  * 1363-2000 recommends SHA-1 and RIPEMD-160.
  63:  * <p>
  64:  * References:
  65:  * <ol>
  66:  * <li><a
  67:  * href="http://www.cosic.esat.kuleuven.ac.be/nessie/workshop/submissions/rsa-pss.zip">
  68:  * RSA-PSS Signature Scheme with Appendix, part B.</a><br>
  69:  * Primitive specification and supporting documentation.<br>
  70:  * Jakob Jonsson and Burt Kaliski.</li>
  71:  * </ol>
  72:  */
  73: public class EMSA_PSS
  74:     implements Cloneable
  75: {
  76:   private static final Logger log = Logger.getLogger(EMSA_PSS.class.getName());
  77: 
  78:   /** The underlying hash function to use with this instance. */
  79:   private IMessageDigest hash;
  80: 
  81:   /** The output size of the hash function in octets. */
  82:   private int hLen;
  83: 
  84:   /**
  85:    * Trivial private constructor to enforce use through Factory method.
  86:    *
  87:    * @param hash the message digest instance to use with this scheme instance.
  88:    */
  89:   private EMSA_PSS(IMessageDigest hash)
  90:   {
  91:     super();
  92: 
  93:     this.hash = hash;
  94:     hLen = hash.hashSize();
  95:   }
  96: 
  97:   /**
  98:    * Returns an instance of this object given a designated name of a hash
  99:    * function.
 100:    *
 101:    * @param mdName the canonical name of a hash function.
 102:    * @return an instance of this object configured for use with the designated
 103:    *         options.
 104:    */
 105:   public static EMSA_PSS getInstance(String mdName)
 106:   {
 107:     IMessageDigest hash = HashFactory.getInstance(mdName);
 108:     return new EMSA_PSS(hash);
 109:   }
 110: 
 111:   public Object clone()
 112:   {
 113:     return getInstance(hash.name());
 114:   }
 115: 
 116:   /**
 117:    * The encoding operation EMSA-PSS-Encode computes the hash of a message
 118:    * <code>M</code> using a hash function and maps the result to an encoded
 119:    * message <code>EM</code> of a specified length using a mask generation
 120:    * function.
 121:    *
 122:    * @param mHash the byte sequence resulting from applying the message digest
 123:    *          algorithm Hash to the message <i>M</i>.
 124:    * @param emBits the maximal bit length of the integer OS2IP(EM), at least
 125:    *          <code>8.hLen + 8.sLen + 9</code>.
 126:    * @param salt the salt to use when encoding the output.
 127:    * @return the encoded message <code>EM</code>, an octet string of length
 128:    *         <code>emLen = CEILING(emBits / 8)</code>.
 129:    * @exception IllegalArgumentException if an exception occurs.
 130:    */
 131:   public byte[] encode(byte[] mHash, int emBits, byte[] salt)
 132:   {
 133:     int sLen = salt.length;
 134:     // 1. If the length of M is greater than the input limitation for the hash
 135:     // function (2**61 - 1 octets for SHA-1) then output "message too long"
 136:     // and stop.
 137:     // 2. Let mHash = Hash(M), an octet string of length hLen.
 138:     if (hLen != mHash.length)
 139:       throw new IllegalArgumentException("wrong hash");
 140:     // 3. If emBits < 8.hLen + 8.sLen + 9, output 'encoding error' and stop.
 141:     if (emBits < (8 * hLen + 8 * sLen + 9))
 142:       throw new IllegalArgumentException("encoding error");
 143:     int emLen = (emBits + 7) / 8;
 144:     // 4. Generate a random octet string salt of length sLen; if sLen = 0,
 145:     // then salt is the empty string.
 146:     // ...passed as argument to accomodate JCE
 147:     // 5. Let M0 = 00 00 00 00 00 00 00 00 || mHash || salt;
 148:     // M0 is an octet string of length 8 + hLen + sLen with eight initial zero
 149:     // octets.
 150:     // 6. Let H = Hash(M0), an octet string of length hLen.
 151:     byte[] H;
 152:     int i;
 153:     synchronized (hash)
 154:       {
 155:         for (i = 0; i < 8; i++)
 156:           hash.update((byte) 0x00);
 157: 
 158:         hash.update(mHash, 0, hLen);
 159:         hash.update(salt, 0, sLen);
 160:         H = hash.digest();
 161:       }
 162:     // 7. Generate an octet string PS consisting of emLen - sLen - hLen - 2
 163:     // zero octets. The length of PS may be 0.
 164:     // 8. Let DB = PS || 01 || salt.
 165:     byte[] DB = new byte[emLen - sLen - hLen - 2 + 1 + sLen];
 166:     DB[emLen - sLen - hLen - 2] = 0x01;
 167:     System.arraycopy(salt, 0, DB, emLen - sLen - hLen - 1, sLen);
 168:     // 9. Let dbMask = MGF(H, emLen - hLen - 1).
 169:     byte[] dbMask = MGF(H, emLen - hLen - 1);
 170:     if (Configuration.DEBUG)
 171:       {
 172:         log.fine("dbMask (encode): " + Util.toString(dbMask));
 173:         log.fine("DB (encode): " + Util.toString(DB));
 174:       }
 175:     // 10. Let maskedDB = DB XOR dbMask.
 176:     for (i = 0; i < DB.length; i++)
 177:       DB[i] = (byte)(DB[i] ^ dbMask[i]);
 178:     // 11. Set the leftmost 8emLen - emBits bits of the leftmost octet in
 179:     // maskedDB to zero.
 180:     DB[0] &= (0xFF >>> (8 * emLen - emBits));
 181:     // 12. Let EM = maskedDB || H || bc, where bc is the single octet with
 182:     // hexadecimal value 0xBC.
 183:     byte[] result = new byte[emLen];
 184:     System.arraycopy(DB, 0, result, 0, emLen - hLen - 1);
 185:     System.arraycopy(H, 0, result, emLen - hLen - 1, hLen);
 186:     result[emLen - 1] = (byte) 0xBC;
 187:     // 13. Output EM.
 188:     return result;
 189:   }
 190: 
 191:   /**
 192:    * The decoding operation EMSA-PSS-Decode recovers the message hash from an
 193:    * encoded message <code>EM</code> and compares it to the hash of
 194:    * <code>M</code>.
 195:    *
 196:    * @param mHash the byte sequence resulting from applying the message digest
 197:    *          algorithm Hash to the message <i>M</i>.
 198:    * @param EM the <i>encoded message</i>, an octet string of length
 199:    *          <code>emLen = CEILING(emBits/8).
 200:    * @param emBits the maximal bit length of the integer OS2IP(EM), at least
 201:    * <code>8.hLen + 8.sLen + 9</code>.
 202:    * @param sLen the length, in octets, of the expected salt.
 203:    * @return <code>true</code> if the result of the verification was
 204:    * <i>consistent</i> with the expected reseult; and <code>false</code> if the
 205:    * result was <i>inconsistent</i>.
 206:    * @exception IllegalArgumentException if an exception occurs.
 207:    */
 208:   public boolean decode(byte[] mHash, byte[] EM, int emBits, int sLen)
 209:   {
 210:     if (Configuration.DEBUG)
 211:       {
 212:         log.fine("mHash: " + Util.toString(mHash));
 213:         log.fine("EM: " + Util.toString(EM));
 214:         log.fine("emBits: " + String.valueOf(emBits));
 215:         log.fine("sLen: " + String.valueOf(sLen));
 216:       }
 217:     if (sLen < 0)
 218:       throw new IllegalArgumentException("sLen");
 219:     // 1. If the length of M is greater than the input limitation for the hash
 220:     // function (2**61 ? 1 octets for SHA-1) then output 'inconsistent' and
 221:     // stop.
 222:     // 2. Let mHash = Hash(M), an octet string of length hLen.
 223:     if (hLen != mHash.length)
 224:       {
 225:         if (Configuration.DEBUG)
 226:           log.fine("hLen != mHash.length; hLen: " + String.valueOf(hLen));
 227:         throw new IllegalArgumentException("wrong hash");
 228:       }
 229:     // 3. If emBits < 8.hLen + 8.sLen + 9, output 'decoding error' and stop.
 230:     if (emBits < (8 * hLen + 8 * sLen + 9))
 231:       {
 232:         if (Configuration.DEBUG)
 233:           log.fine("emBits < (8hLen + 8sLen + 9); sLen: "
 234:                    + String.valueOf(sLen));
 235:         throw new IllegalArgumentException("decoding error");
 236:       }
 237:     int emLen = (emBits + 7) / 8;
 238:     // 4. If the rightmost octet of EM does not have hexadecimal value bc,
 239:     // output 'inconsistent' and stop.
 240:     if ((EM[EM.length - 1] & 0xFF) != 0xBC)
 241:       {
 242:         if (Configuration.DEBUG)
 243:           log.fine("EM does not end with 0xBC");
 244:         return false;
 245:       }
 246:     // 5. Let maskedDB be the leftmost emLen ? hLen ? 1 octets of EM, and let
 247:     // H be the next hLen octets.
 248:     // 6. If the leftmost 8.emLen ? emBits bits of the leftmost octet in
 249:     // maskedDB are not all equal to zero, output 'inconsistent' and stop.
 250:     if ((EM[0] & (0xFF << (8 - (8 * emLen - emBits)))) != 0)
 251:       {
 252:         if (Configuration.DEBUG)
 253:           log.fine("Leftmost 8emLen - emBits bits of EM are not 0s");
 254:         return false;
 255:       }
 256:     byte[] DB = new byte[emLen - hLen - 1];
 257:     byte[] H = new byte[hLen];
 258:     System.arraycopy(EM, 0, DB, 0, emLen - hLen - 1);
 259:     System.arraycopy(EM, emLen - hLen - 1, H, 0, hLen);
 260:     // 7. Let dbMask = MGF(H, emLen ? hLen ? 1).
 261:     byte[] dbMask = MGF(H, emLen - hLen - 1);
 262:     // 8. Let DB = maskedDB XOR dbMask.
 263:     int i;
 264:     for (i = 0; i < DB.length; i++)
 265:       DB[i] = (byte)(DB[i] ^ dbMask[i]);
 266:     // 9. Set the leftmost 8.emLen ? emBits bits of DB to zero.
 267:     DB[0] &= (0xFF >>> (8 * emLen - emBits));
 268:     if (Configuration.DEBUG)
 269:       {
 270:         log.fine("dbMask (decode): " + Util.toString(dbMask));
 271:         log.fine("DB (decode): " + Util.toString(DB));
 272:       }
 273:     // 10. If the emLen -hLen -sLen -2 leftmost octets of DB are not zero or
 274:     // if the octet at position emLen -hLen -sLen -1 is not equal to 0x01,
 275:     // output 'inconsistent' and stop.
 276:     // IMPORTANT (rsn): this is an error in the specs, the index of the 0x01
 277:     // byte should be emLen -hLen -sLen -2 and not -1! authors have been advised
 278:     for (i = 0; i < (emLen - hLen - sLen - 2); i++)
 279:       {
 280:         if (DB[i] != 0)
 281:           {
 282:             if (Configuration.DEBUG)
 283:               log.fine("DB[" + String.valueOf(i) + "] != 0x00");
 284:             return false;
 285:           }
 286:       }
 287:     if (DB[i] != 0x01)
 288:       { // i == emLen -hLen -sLen -2
 289:         if (Configuration.DEBUG)
 290:           log.fine("DB's byte at position (emLen -hLen -sLen -2); i.e. "
 291:                    + String.valueOf(i) + " is not 0x01");
 292:         return false;
 293:       }
 294:     // 11. Let salt be the last sLen octets of DB.
 295:     byte[] salt = new byte[sLen];
 296:     System.arraycopy(DB, DB.length - sLen, salt, 0, sLen);
 297:     // 12. Let M0 = 00 00 00 00 00 00 00 00 || mHash || salt;
 298:     // M0 is an octet string of length 8 + hLen + sLen with eight initial
 299:     // zero octets.
 300:     // 13. Let H0 = Hash(M0), an octet string of length hLen.
 301:     byte[] H0;
 302:     synchronized (hash)
 303:       {
 304:         for (i = 0; i < 8; i++)
 305:           hash.update((byte) 0x00);
 306: 
 307:         hash.update(mHash, 0, hLen);
 308:         hash.update(salt, 0, sLen);
 309:         H0 = hash.digest();
 310:       }
 311:     // 14. If H = H0, output 'consistent.' Otherwise, output 'inconsistent.'
 312:     return Arrays.equals(H, H0);
 313:   }
 314: 
 315:   /**
 316:    * A mask generation function takes an octet string of variable length and a
 317:    * desired output length as input, and outputs an octet string of the desired
 318:    * length. There may be restrictions on the length of the input and output
 319:    * octet strings, but such bounds are generally very large. Mask generation
 320:    * functions are deterministic; the octet string output is completely
 321:    * determined by the input octet string. The output of a mask generation
 322:    * function should be pseudorandom, that is, it should be infeasible to
 323:    * predict, given one part of the output but not the input, another part of
 324:    * the output. The provable security of RSA-PSS relies on the random nature of
 325:    * the output of the mask generation function, which in turn relies on the
 326:    * random nature of the underlying hash function.
 327:    *
 328:    * @param Z a seed.
 329:    * @param l the desired output length in octets.
 330:    * @return the mask.
 331:    * @exception IllegalArgumentException if the desired output length is too
 332:    *              long.
 333:    */
 334:   private byte[] MGF(byte[] Z, int l)
 335:   {
 336:     // 1. If l > (2**32).hLen, output 'mask too long' and stop.
 337:     if (l < 1 || (l & 0xFFFFFFFFL) > ((hLen & 0xFFFFFFFFL) << 32L))
 338:       throw new IllegalArgumentException("mask too long");
 339:     // 2. Let T be the empty octet string.
 340:     byte[] result = new byte[l];
 341:     // 3. For i = 0 to CEILING(l/hLen) ? 1, do
 342:     int limit = ((l + hLen - 1) / hLen) - 1;
 343:     IMessageDigest hashZ = null;
 344:     hashZ = (IMessageDigest) hash.clone();
 345:     hashZ.digest();
 346:     hashZ.update(Z, 0, Z.length);
 347:     IMessageDigest hashZC = null;
 348:     byte[] t;
 349:     int sofar = 0;
 350:     int length;
 351:     for (int i = 0; i < limit; i++)
 352:       {
 353:         // 3.1 Convert i to an octet string C of length 4 with the primitive
 354:         // I2OSP: C = I2OSP(i, 4).
 355:         // 3.2 Concatenate the hash of the seed Z and C to the octet string T:
 356:         // T = T || Hash(Z || C)
 357:         hashZC = (IMessageDigest) hashZ.clone();
 358:         hashZC.update((byte)(i >>> 24));
 359:         hashZC.update((byte)(i >>> 16));
 360:         hashZC.update((byte)(i >>> 8));
 361:         hashZC.update((byte) i);
 362:         t = hashZC.digest();
 363:         length = l - sofar;
 364:         length = (length > hLen ? hLen : length);
 365:         System.arraycopy(t, 0, result, sofar, length);
 366:         sofar += length;
 367:       }
 368:     // 4. Output the leading l octets of T as the octet string mask.
 369:     return result;
 370:   }
 371: }