Throw if ECKey.recoverPubBytesFromSignature results in point at infinity

ethereum · May 3, 2018 · df3350b · df3350b
1 parent 17dfc1e
commit df3350b
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diff --git a/ethereumj-core/src/main/java/org/ethereum/crypto/ECKey.java b/ethereumj-core/src/main/java/org/ethereum/crypto/ECKey.java
@@ -1107,6 +1107,9 @@ public static byte[] recoverPubBytesFromSignature(int recId, ECDSASignature sig,
         BigInteger srInv = rInv.multiply(sig.s).mod(n);
         BigInteger eInvrInv = rInv.multiply(eInv).mod(n);
         ECPoint.Fp q = (ECPoint.Fp) ECAlgorithms.sumOfTwoMultiplies(CURVE.getG(), eInvrInv, R, srInv);
+        // result sanity check: point must not be at infinity
+        if (q.isInfinity())
+            return null;
         return q.getEncoded(/* compressed */ false);
     }
 

diff --git a/ethereumj-core/src/test/java/org/ethereum/crypto/ECKeyTest.java b/ethereumj-core/src/test/java/org/ethereum/crypto/ECKeyTest.java
@@ -250,6 +250,22 @@ public void testVerifySignature3() throws SignatureException {
         // todo: add test assertion when the sign/verify part actually works.
     }
 
+    @Test // result is a point at infinity
+    public void testVerifySignature4() {
+
+        byte[] hash = Hex.decode("acb1c19ac0832320815b5e886c6b73ad7d6177853d44b026f2a7a9e11bb899fc");
+        byte[] r = Hex.decode("89ea49159b334f9aebbf54481b69d000d285baa341899db355a4030f6838394e");
+        byte[] s = Hex.decode("540e9f9fa17bef441e32d98d5f4554cfefdc6a56101352e4b92efafd0d9646e8");
+        byte v = (byte) 28;
+
+        ECDSASignature sig = ECKey.ECDSASignature.fromComponents(r, s, v);
+
+        try {
+            ECKey.signatureToKey(hash, sig);
+            fail("Result is a point at infinity, recovery must fail");
+        } catch (SignatureException e) {
+        }
+    }
 
     @Test
     public void testSValue() throws Exception {