* Digital signatures when transmitted in an X.509 certificates are encoded * in DER (Distinguished Encoding Rules) as a BIT STRING; i.e. * *
* Certificate ::= SEQUENCE {
* tbsCertificate TBSCertificate,
* signatureAlgorithm AlgorithmIdentifier,
* signature BIT STRING
* }
*
* * The output of the encoder, and the input of the decoder, of this codec are * then the raw bytes of such a BIT STRING; i.e. not the DER-encoded * form itself. *
* RFC-2459 states that, for the Digital Signature Standard (DSS), which
* generates two MPIs, commonly called r and s, as the
* result of digitally signing a message, these two numbers will be transferred
* as the following ASN.1 structure:
*
*
* Dss-Sig-Value ::= SEQUENCE {
* r INTEGER,
* s INTEGER
* }
*
* * Client code that needs to build a DER BIT STRING MUST construct such * an ASN.1 value. The following is an example of how to do this: *
*
* ... * import gnu.java.security.der.BitString; * import gnu.java.security.der.DER; * import gnu.java.security.der.DERValue; * ... * DERValue bitString = new DERValue(DER.BIT_STRING, new BitString(sigBytes)); * ... **/ public class DSSSignatureX509Codec implements ISignatureCodec { // implicit 0-arguments constructor public int getFormatID() { return Registry.X509_ENCODING_ID; } /** * Encodes a DSS Signature output as the signature raw bytes which can * be used to construct an ASN.1 DER-encoded BIT STRING as defined in the * documentation of this class. * * @param signature the output of the DSS signature algorithm; i.e. the value * returned by the invocation of * {@link gnu.java.security.sig.ISignature#sign()} method. In the * case of a DSS signature this is an array of two MPIs called *
r and s.
* @return the raw bytes of a DSS signature which could be then used as the
* contents of a BIT STRING as per rfc-2459.
* @throws InvalidParameterException if an exception occurs during the
* marshalling process.
*/
public byte[] encodeSignature(Object signature)
{
BigInteger[] rs = (BigInteger[]) signature;
DERValue derR = new DERValue(DER.INTEGER, rs[0]);
DERValue derS = new DERValue(DER.INTEGER, rs[1]);
ArrayList dssSigValue = new ArrayList(2);
dssSigValue.add(derR);
dssSigValue.add(derS);
DERValue derDssSigValue = new DERValue(DER.CONSTRUCTED | DER.SEQUENCE,
dssSigValue);
byte[] result;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
try
{
DERWriter.write(baos, derDssSigValue);
result = baos.toByteArray();
}
catch (IOException x)
{
InvalidParameterException y = new InvalidParameterException();
y.initCause(x);
throw y;
}
return result;
}
/**
* Decodes a signature as defined in the documentation of this class.
*
* @param input the byte array to unmarshall into a valid DSS signature
* instance; i.e. an array of two MPIs. MUST NOT be null.
* @return an array of two MPIs, r and s in this
* order, decoded from the designated input.
* @throw InvalidParameterException if an exception occurs during the
* unmarshalling process.
*/
public Object decodeSignature(byte[] input)
{
if (input == null)
throw new InvalidParameterException("Input bytes MUST NOT be null");
BigInteger r, s;
DERReader der = new DERReader(input);
try
{
DERValue derDssSigValue = der.read();
DerUtil.checkIsConstructed(derDssSigValue, "Wrong Dss-Sig-Value field");
DERValue val = der.read();
DerUtil.checkIsBigInteger(val, "Wrong R field");
r = (BigInteger) val.getValue();
val = der.read();
DerUtil.checkIsBigInteger(val, "Wrong S field");
s = (BigInteger) val.getValue();
}
catch (IOException x)
{
InvalidParameterException y = new InvalidParameterException();
y.initCause(x);
throw y;
}
return new BigInteger[] { r, s };
}
}