Handle leading zeros in (r|s)-parameters of ECDSA signature

org/xbill/DNS/DNSSEC.java

@@ -775,42 +775,86 @@ private static class ECKeyInfo {
 	return signature;
 }
 
-private static byte []
-ECDSASignaturefromDNS(byte [] signature, ECKeyInfo keyinfo)
-	throws DNSSECException, IOException
-{
-	if (signature.length != keyinfo.length * 2)
-		throw new SignatureVerificationException();
-
-	DNSInput in = new DNSInput(signature);
-	DNSOutput out = new DNSOutput();
-
-	byte [] r = in.readByteArray(keyinfo.length);
-	int rlen = keyinfo.length;
-	if (r[0] < 0)
-		rlen++;
-
-	byte [] s = in.readByteArray(keyinfo.length);
-	int slen = keyinfo.length;
-	if (s[0] < 0)
-		slen++;
-
-	out.writeU8(ASN1_SEQ);
-	out.writeU8(rlen + slen + 4);
-
-	out.writeU8(ASN1_INT);
-	out.writeU8(rlen);
-	if (rlen > keyinfo.length)
-		out.writeU8(0);
-	out.writeByteArray(r);
-
-	out.writeU8(ASN1_INT);
-	out.writeU8(slen);
-	if (slen > keyinfo.length)
-		out.writeU8(0);
-	out.writeByteArray(s);
+/**
+ * 
+ * Convert a DNS standard ECDSA signature (defined in RFC 6605) into a JCE
+ * standard ECDSA signature, which is encoded in ASN.1.
+ * 
+ * The format of the ASN.1 signature is
+ * 
+ * ASN1_SEQ . seq_length . ASN1_INT . r_length . R . ANS1_INT . s_length . S
+ * 
+ * where R and S may have a leading zero byte if without it the values would be
+ * negative.
+ *
+ * The format of the DNSSEC signature is just R . S where R and S are both
+ * exactly "length" bytes.
+ * 
+ * @param signature
+ *            The binary signature data from an RRSIG record.
+ * @return signature data that may be used in a JCE Signature object for
+ *         verification purposes.
+ */
+public static byte[] convertECDSASignature(byte[] signature) {
+	/**
+	 * This method is a patch for the problem of leading zeros that keep the the
+	 * public key from being verified even if it is valid
+	 * See: https://github.com/ibauersachs/dnssecjava/issues/14
+	 * 
+	 * This patch was obtained from:
+	 * https://github.com/dblacka/jdnssec-tools/pull/4/commits/ca2a9324858b6b5a87fde8ce8a5fb2365c85db35
+	 * and
+	 * https://github.com/gryphius/dnsjava/commit/b4216b35a8386cf47e2c59a875c655d584624d1d
+	 */
+	{
+		byte r_src_pos, r_src_len, r_pad, s_src_pos, s_src_len, s_pad, len;
+
+		r_src_len = s_src_len = (byte) (signature.length / 2);
+		r_src_pos = 0;
+		r_pad = 0;
+		s_src_pos = (byte) (r_src_pos + r_src_len);
+		s_pad = 0;
+		len = (byte) (6 + r_src_len + s_src_len);
+
+		// multiple leading zeroes are forbidden
+		while (signature[r_src_pos] == 0 && r_src_len > 0) {
+			r_src_pos++;
+			r_src_len--;
+			len--;
+		}
+		while (signature[s_src_pos] == 0 && s_src_len > 0) {
+			s_src_pos++;
+			s_src_len--;
+			len--;
+		}
 
-	return out.toByteArray();
+		// except when they are mandatory
+		if (r_src_len > 0 && signature[r_src_pos] < 0) {
+			r_pad = 1;
+			len++;
+		}
+		if (s_src_len > 0 && signature[s_src_pos] < 0) {
+			s_pad = 1;
+			len++;
+		}
+		byte[] sig = new byte[len];
+		byte pos = 0;
+
+		sig[pos++] = ASN1_SEQ;
+		sig[pos++] = (byte) (len - 2);
+		sig[pos++] = ASN1_INT;
+		sig[pos++] = (byte) (r_src_len + r_pad);
+		pos += r_pad;
+		System.arraycopy(signature, r_src_pos, sig, pos, r_src_len);
+		pos += r_src_len;
+
+		sig[pos++] = ASN1_INT;
+		sig[pos++] = (byte) (s_src_len + s_pad);
+		pos += s_pad;
+		System.arraycopy(signature, s_src_pos, sig, pos, s_src_len);
+
+		return sig;
+	}
 }
 
 private static byte []
@@ -869,12 +913,10 @@ private static class ECKeyInfo {
 								   GOST);
 				break;
 			case Algorithm.ECDSAP256SHA256:
-				signature = ECDSASignaturefromDNS(signature,
-								  ECDSA_P256);
+				signature = convertECDSASignature(signature);
 				break;
 			case Algorithm.ECDSAP384SHA384:
-				signature = ECDSASignaturefromDNS(signature,
-								  ECDSA_P384);
+				signature = convertECDSASignature(signature);
 				break;
 			default:
 				throw new UnsupportedAlgorithmException(alg);