libjava/classpath/gnu/java/security/sig/dss/DSSSignatureX509Codec.java

   1 /* DSSSignatureX509Codec.java -- X.509 encoder/decoder for DSS signatures
   2    Copyright (C) 2006 Free Software Foundation, Inc.
   3
   4 This file is 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, or (at your option)
   9 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; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 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
  33 or based on this library.  If you modify this library, you may extend
  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.dss;
  40
  41 import gnu.java.security.Registry;
  42 import gnu.java.security.der.DER;
  43 import gnu.java.security.der.DERReader;
  44 import gnu.java.security.der.DERValue;
  45 import gnu.java.security.der.DERWriter;
  46 import gnu.java.security.sig.ISignatureCodec;
  47 import gnu.java.security.util.DerUtil;
  48
  49 import java.io.ByteArrayOutputStream;
  50 import java.io.IOException;
  51 import java.math.BigInteger;
  52 import java.security.InvalidParameterException;
  53 import java.util.ArrayList;
  54
  55 /**
  56  * An implementation of an {@link ISignatureCodec} that knows to encode and
  57  * decode DSS signatures into the raw bytes which would constitute a DER-encoded
  58  * form of the ASN.1 structure defined in RFC-2459, and RFC-2313 as described in
  59  * the next paragraphs.
  60  * <p>
  61  * Digital signatures when transmitted in an X.509 certificates are encoded
  62  * in DER (Distinguished Encoding Rules) as a BIT STRING; i.e.
  63  *
  64  * <pre>
  65  * Certificate ::= SEQUENCE {
  66  *   tbsCertificate       TBSCertificate,
  67  *   signatureAlgorithm   AlgorithmIdentifier,
  68  *   signature            BIT STRING
  69  * }
  70  * </pre>
  71  * <p>
  72  * The output of the encoder, and the input of the decoder, of this codec are
  73  * then the <i>raw</i> bytes of such a BIT STRING; i.e. not the DER-encoded
  74  * form itself.
  75  * <p>
  76  * RFC-2459 states that, for the Digital Signature Standard (DSS), which
  77  * generates two MPIs, commonly called <code>r</code> and <code>s</code>, as the
  78  * result of digitally signing a message, these two numbers will be transferred
  79  * as the following ASN.1 structure:
  80  *
  81  * <pre>
  82  *   Dss-Sig-Value ::= SEQUENCE {
  83  *     r  INTEGER,
  84  *     s  INTEGER
  85  *   }
  86  * </pre>
  87  * <p>
  88  * Client code that needs to build a DER BIT STRING <b>MUST</b> construct such
  89  * an ASN.1 value. The following is an example of how to do this:
  90  * <p>
  91  * <pre>
  92  * ...
  93  * import gnu.java.security.der.BitString;
  94  * import gnu.java.security.der.DER;
  95  * import gnu.java.security.der.DERValue;
  96  * ...
  97  * DERValue bitString = new DERValue(DER.BIT_STRING, new BitString(sigBytes));
  98  * ...
  99  * </pre>
 100  */
 101 public class DSSSignatureX509Codec
 102     implements ISignatureCodec
 103 {
 104   // implicit 0-arguments constructor
 105
 106   public int getFormatID()
 107   {
 108     return Registry.X509_ENCODING_ID;
 109   }
 110
 111   /**
 112    * Encodes a DSS Signature output as the <i>signature</i> raw bytes which can
 113    * be used to construct an ASN.1 DER-encoded BIT STRING as defined in the
 114    * documentation of this class.
 115    *
 116    * @param signature the output of the DSS signature algorithm; i.e. the value
 117    *          returned by the invocation of
 118    *          {@link gnu.java.security.sig.ISignature#sign()} method. In the
 119    *          case of a DSS signature this is an array of two MPIs called
 120    *          <code>r</code> and <code>s</code>.
 121    * @return the raw bytes of a DSS signature which could be then used as the
 122    *         contents of a BIT STRING as per rfc-2459.
 123    * @throws InvalidParameterException if an exception occurs during the
 124    *           marshalling process.
 125    */
 126   public byte[] encodeSignature(Object signature)
 127   {
 128     BigInteger[] rs = (BigInteger[]) signature;
 129
 130     DERValue derR = new DERValue(DER.INTEGER, rs[0]);
 131     DERValue derS = new DERValue(DER.INTEGER, rs[1]);
 132
 133     ArrayList dssSigValue = new ArrayList(2);
 134     dssSigValue.add(derR);
 135     dssSigValue.add(derS);
 136     DERValue derDssSigValue = new DERValue(DER.CONSTRUCTED | DER.SEQUENCE,
 137                                            dssSigValue);
 138     byte[] result;
 139     ByteArrayOutputStream baos = new ByteArrayOutputStream();
 140     try
 141       {
 142         DERWriter.write(baos, derDssSigValue);
 143         result = baos.toByteArray();
 144       }
 145     catch (IOException x)
 146       {
 147         InvalidParameterException y = new InvalidParameterException();
 148         y.initCause(x);
 149         throw y;
 150       }
 151
 152     return result;
 153   }
 154
 155   /**
 156    * Decodes a <i>signature</i> as defined in the documentation of this class.
 157    *
 158    * @param input the byte array to unmarshall into a valid DSS signature
 159    *          instance; i.e. an array of two MPIs. MUST NOT be null.
 160    * @return an array of two MPIs, <code>r</code> and <code>s</code> in this
 161    *         order, decoded from the designated <code>input</code>.
 162    * @throw InvalidParameterException if an exception occurs during the
 163    *        unmarshalling process.
 164    */
 165   public Object decodeSignature(byte[] input)
 166   {
 167     if (input == null)
 168       throw new InvalidParameterException("Input bytes MUST NOT be null");
 169
 170     BigInteger r, s;
 171     DERReader der = new DERReader(input);
 172     try
 173       {
 174         DERValue derDssSigValue = der.read();
 175         DerUtil.checkIsConstructed(derDssSigValue, "Wrong Dss-Sig-Value field");
 176
 177         DERValue val = der.read();
 178         DerUtil.checkIsBigInteger(val, "Wrong R field");
 179         r = (BigInteger) val.getValue();
 180         val = der.read();
 181         DerUtil.checkIsBigInteger(val, "Wrong S field");
 182         s = (BigInteger) val.getValue();
 183       }
 184     catch (IOException x)
 185       {
 186         InvalidParameterException y = new InvalidParameterException();
 187         y.initCause(x);
 188         throw y;
 189       }
 190
 191     return new BigInteger[] { r, s };
 192   }
 193 }