grind for low r, for psbt ensure if a witness UTXO is provided, no non-witness signature may be created

src/main/java/com/sparrowwallet/drongo/crypto/ECKey.java

@@ -461,6 +461,10 @@ public class ECKey implements EncryptableItem {
             return bos;
         }
 
+        protected boolean hasLowR() {
+            return r.toByteArray().length <= 32;
+        }
+
         @Override
         public boolean equals(Object o) {
             if (this == o) return true;
@@ -517,11 +521,18 @@ public class ECKey implements EncryptableItem {
             throw new IllegalArgumentException("Private key cannot be null");
         }
 
-        ECDSASigner signer = new ECDSASigner(new HMacDSAKCalculator(new SHA256Digest()));
+        ECDSASignature signature;
+        int counter = 0;
+        do {
+            ECDSASigner signer = new ECDSASigner(new HMacDSANonceKCalculator(new SHA256Digest(), counter));
             ECPrivateKeyParameters privKey = new ECPrivateKeyParameters(privateKeyForSigning, CURVE);
             signer.init(true, privKey);
             BigInteger[] components = signer.generateSignature(input.getBytes());
-        return new ECDSASignature(components[0], components[1]).toCanonicalised();
+            signature = new ECDSASignature(components[0], components[1]).toCanonicalised();
+            counter++;
+        } while(!signature.hasLowR());
+
+        return signature;
     }
 
     /**

src/main/java/com/sparrowwallet/drongo/crypto/HMacDSANonceKCalculator.java

@@ -0,0 +1,160 @@
+package com.sparrowwallet.drongo.crypto;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+import com.sparrowwallet.drongo.Utils;
+import org.bouncycastle.crypto.Digest;
+import org.bouncycastle.crypto.macs.HMac;
+import org.bouncycastle.crypto.params.KeyParameter;
+import org.bouncycastle.crypto.signers.DSAKCalculator;
+import org.bouncycastle.util.Arrays;
+import org.bouncycastle.util.BigIntegers;
+
+/**
+ * A deterministic K calculator based on the algorithm in section 3.2 of RFC 6979.
+ * This is a copy of org.bouncycastle.crypto.signers.HMacDSAKCalculator, with support for section 3.6 of RFC 6979 (additional data)
+ */
+public class HMacDSANonceKCalculator implements DSAKCalculator {
+    private static final BigInteger ZERO = BigInteger.valueOf(0);
+
+    private final HMac hMac;
+    private final byte[] K;
+    private final byte[] V;
+    private final long counter;
+
+    private BigInteger n;
+
+    /**
+     * Base constructor.
+     *
+     * @param digest digest to build the HMAC on.
+     * @param counter additional data as per RFC 6979 3.6
+     */
+    public HMacDSANonceKCalculator(Digest digest, int counter) {
+        this.hMac = new HMac(digest);
+        this.V = new byte[hMac.getMacSize()];
+        this.K = new byte[hMac.getMacSize()];
+        this.counter = Integer.toUnsignedLong(counter);
+    }
+
+    public boolean isDeterministic()
+    {
+        return true;
+    }
+
+    public void init(BigInteger n, SecureRandom random)
+    {
+        throw new IllegalStateException("Operation not supported");
+    }
+
+    public void init(BigInteger n, BigInteger d, byte[] message)
+    {
+        this.n = n;
+
+        Arrays.fill(V, (byte)0x01);
+        Arrays.fill(K, (byte)0);
+
+        int size = BigIntegers.getUnsignedByteLength(n);
+        byte[] x = new byte[size];
+        byte[] dVal = BigIntegers.asUnsignedByteArray(d);
+
+        System.arraycopy(dVal, 0, x, x.length - dVal.length, dVal.length);
+
+        byte[] m = new byte[size];
+
+        BigInteger mInt = bitsToInt(message);
+
+        if (mInt.compareTo(n) >= 0)
+        {
+            mInt = mInt.subtract(n);
+        }
+
+        byte[] mVal = BigIntegers.asUnsignedByteArray(mInt);
+
+        System.arraycopy(mVal, 0, m, m.length - mVal.length, mVal.length);
+
+        BigInteger additional = BigInteger.valueOf(counter);
+        byte[] aData = Utils.bigIntegerToBytes(additional, size);
+
+        hMac.init(new KeyParameter(K));
+
+        hMac.update(V, 0, V.length);
+        hMac.update((byte)0x00);
+        hMac.update(x, 0, x.length);
+        hMac.update(m, 0, m.length);
+        hMac.update(aData, 0, aData.length);
+
+        hMac.doFinal(K, 0);
+
+        hMac.init(new KeyParameter(K));
+
+        hMac.update(V, 0, V.length);
+
+        hMac.doFinal(V, 0);
+
+        hMac.update(V, 0, V.length);
+        hMac.update((byte)0x01);
+        hMac.update(x, 0, x.length);
+        hMac.update(m, 0, m.length);
+
+        hMac.doFinal(K, 0);
+
+        hMac.init(new KeyParameter(K));
+
+        hMac.update(V, 0, V.length);
+
+        hMac.doFinal(V, 0);
+    }
+
+    public BigInteger nextK()
+    {
+        byte[] t = new byte[BigIntegers.getUnsignedByteLength(n)];
+
+        for (;;)
+        {
+            int tOff = 0;
+
+            while (tOff < t.length)
+            {
+                hMac.update(V, 0, V.length);
+
+                hMac.doFinal(V, 0);
+
+                int len = Math.min(t.length - tOff, V.length);
+                System.arraycopy(V, 0, t, tOff, len);
+                tOff += len;
+            }
+
+            BigInteger k = bitsToInt(t);
+
+            if (k.compareTo(ZERO) > 0 && k.compareTo(n) < 0)
+            {
+                return k;
+            }
+
+            hMac.update(V, 0, V.length);
+            hMac.update((byte)0x00);
+
+            hMac.doFinal(K, 0);
+
+            hMac.init(new KeyParameter(K));
+
+            hMac.update(V, 0, V.length);
+
+            hMac.doFinal(V, 0);
+        }
+    }
+
+    private BigInteger bitsToInt(byte[] t)
+    {
+        BigInteger v = new BigInteger(1, t);
+
+        if (t.length * 8 > n.bitLength())
+        {
+            v = v.shiftRight(t.length * 8 - n.bitLength());
+        }
+
+        return v;
+    }
+}

src/main/java/com/sparrowwallet/drongo/psbt/PSBTInput.java

@@ -334,7 +334,7 @@ public class PSBTInput {
 
     public Script getSigningScript() {
         int vout = (int)transaction.getInputs().get(index).getOutpoint().getIndex();
-        Script signingScript = getNonWitnessUtxo() != null ? getNonWitnessUtxo().getOutputs().get(vout).getScript() : getWitnessUtxo().getScript();
+        Script signingScript = getWitnessUtxo() != null ? getWitnessUtxo().getScript() : getNonWitnessUtxo().getOutputs().get(vout).getScript();
 
         if(P2SH.isScriptType(signingScript)) {
             if(getRedeemScript() != null) {
@@ -363,11 +363,11 @@ public class PSBTInput {
 
     private Sha256Hash getHashForSignature(Script connectedScript, SigHash localSigHash) {
         Sha256Hash hash;
-        if (getNonWitnessUtxo() != null) {
+        if(getWitnessUtxo() != null) {
-            hash = transaction.hashForSignature(index, connectedScript, localSigHash);
-        } else {
             long prevValue = getWitnessUtxo().getValue();
             hash = transaction.hashForWitnessSignature(index, connectedScript, prevValue, localSigHash);
+        } else {
+            hash = transaction.hashForSignature(index, connectedScript, localSigHash);
         }
 
         return hash;