// Copyright (c) 1999-2004 Brian Wellington (bwelling@xbill.org)
package org.xbill.DNS.security;
import java.security.SignatureException;
import java.security.interfaces.DSAParams;
import java.util.Arrays;
import org.xbill.DNS.*;
/**
* Converts DSA signatures between the SIG record format (as specified
* in RFC 2536) and the format used by Java DSA routines (DER-encoded).
*
* @author Brian Wellington
*/
public class DSASignature {
static final int ASN1_SEQ = 0x30;
static final int ASN1_INT = 0x2;
private DSASignature() {}
/**
* Converts the signature field in a SIG record to the
* format expected by the DSA verification routines.
*/
static byte []
create(SIGRecord sigrec) {
final int len = 20;
int n = 0;
byte rlen, slen, seqlen;
byte [] sigdata = sigrec.getSignature();
rlen = len;
if (sigdata[1] < 0)
rlen++;
slen = len;
if (sigdata[1] < 0)
slen++;
/* 4 = 2 * (INT, value) */
seqlen = (byte) (rlen + slen + 4);
/* 2 = 1 * (SEQ, value) */
byte [] array = new byte[seqlen + 2];
array[n++] = ASN1_SEQ;
array[n++] = (byte) seqlen;
array[n++] = ASN1_INT;
array[n++] = rlen;
if (rlen > len)
array[n++] = 0;
for (int i = 0; i < len; i++, n++)
array[n] = sigdata[1 + i];
array[n++] = ASN1_INT;
array[n++] = slen;
if (slen > len)
array[n++] = 0;
for (int i = 0; i < len; i++, n++)
array[n] = sigdata[1 + len + i];
return array;
}
/**
* Converts the signature generated by DSA signature routines to
* the one expected inside a SIG record.
*/
static byte []
create(DSAParams params, byte [] sig)
throws SignatureException
{
int rLength, sLength;
int rOffset, sOffset;
if ((sig[0] != ASN1_SEQ) || (sig[2] != ASN1_INT))
throw new SignatureException("Expected SEQ, INT");
rLength = sig[3];
rOffset = 4;
if (sig[rOffset] == 0) {
rLength--;
rOffset++;
}
if (sig[rOffset+rLength] != ASN1_INT)
throw new SignatureException("Expected INT");
sLength = sig[rOffset + rLength + 1];
sOffset = rOffset + rLength + 2;
if (sig[sOffset] == 0) {
sLength--;
sOffset++;
}
if ((rLength > 20) || (sLength > 20))
throw new SignatureException("DSA R/S too long");
byte[] newSig = new byte[41];
Arrays.fill(newSig, (byte) 0);
newSig[0] = (byte) ((params.getP().bitLength() - 512)/64);
System.arraycopy(sig, rOffset, newSig, 1 + (20 - rLength), rLength);
System.arraycopy(sig, sOffset, newSig, 21 + (20 - sLength), sLength);
return newSig;
}
}