fix(sdk): parse the component sizes (#286)

we serialize the components `r` and `s` of an ECDSA signature as: ``` | length of r in bytes (1 byte) | r | length of s in bytes (1 byte) | s | ``` The change to the spec is implemented [here](opentdf/spec#17) and hasn't been merged yet --------- Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: mkleene

sdk/src/main/java/io/opentdf/platform/sdk/ECCMode.java

@@ -55,12 +55,6 @@ public byte getECCModeAsByte() {
  return (byte) value;
  }
 
- public static int getECDSASignatureStructSize(NanoTDFType.ECCurve curve) {
- int keySize = curve.getKeySize();
- return (1 + keySize + 1 + keySize);
- }
-
-
  @Nonnull
  public NanoTDFType.ECCurve getCurve() {
  return NanoTDFType.ECCurve.fromCurveMode(data.curveMode);

sdk/src/main/java/io/opentdf/platform/sdk/PolicyInfo.java

@@ -3,8 +3,8 @@
 import java.nio.ByteBuffer;
 
 public class PolicyInfo {
+ private static final int DEFAULT_BINDING_SIZE = 8;
  private NanoTDFType.PolicyType type;
- private boolean hasECDSABinding;
  private byte[] body;
  private byte[] binding;
 
@@ -13,7 +13,6 @@ public PolicyInfo() {
 
  public PolicyInfo(ByteBuffer buffer, ECCMode eccMode) {
  this.type = NanoTDFType.PolicyType.values()[buffer.get()];
- this.hasECDSABinding = eccMode.isECDSABindingEnabled();
 
  if (this.type == NanoTDFType.PolicyType.REMOTE_POLICY) {
 
@@ -45,13 +44,40 @@ public PolicyInfo(ByteBuffer buffer, ECCMode eccMode) {
  }
  }
 
- int bindingBytesSize = 8; // GMAC length
- if (this.hasECDSABinding) { // ECDSA - The size of binding depends on the curve.
- bindingBytesSize = ECCMode.getECDSASignatureStructSize(eccMode.getCurve());
+ this.binding = readBinding(buffer, eccMode);
+ }
+
+ static byte[] readBinding(ByteBuffer buffer, ECCMode eccMode) {
+ byte[] binding;
+ if (eccMode.isECDSABindingEnabled()) { // ECDSA - The size of binding depends on the curve.
+ int rSize = getSize(buffer.get(), eccMode.getCurve());
+ byte[] rBytes = new byte[rSize];
+ buffer.get(rBytes);
+ int sSize = getSize(buffer.get(), eccMode.getCurve());
+ byte[] sBytes = new byte[sSize];
+ buffer.get(sBytes);
+ binding = ByteBuffer.allocate(rSize + sSize + 2)
+ .put((byte) rSize)
+ .put(rBytes)
+ .put((byte) sSize)
+ .put(sBytes)
+ .array();
+ } else {
+ binding = new byte[DEFAULT_BINDING_SIZE];
+ buffer.get(binding);
  }
 
- this.binding = new byte[bindingBytesSize];
- buffer.get(this.binding);
+ return binding;
+ }
+
+ private static int getSize(byte size, NanoTDFType.ECCurve curve) {
+ int elementSize = Byte.toUnsignedInt(size);
+ if (elementSize > curve.getKeySize()) {
+ throw new SDK.MalformedTDFException(
+ String.format("Invalid ECDSA binding size. Expected signature components to be at most %d bytes but got (%d) bytes for curve %s.",
+ curve.getKeySize(), elementSize, curve.getCurveName()));
+ }
+ return elementSize;
  }
 
  public int getTotalSize() {
@@ -64,7 +90,6 @@ public int getTotalSize() {
  if (type == NanoTDFType.PolicyType.EMBEDDED_POLICY_PLAIN_TEXT ||
  type == NanoTDFType.PolicyType.EMBEDDED_POLICY_ENCRYPTED) {
 
- int policySize = body.length;
  totalSize = (1 + Short.BYTES + body.length + binding.length);
  } else {
  throw new RuntimeException("Embedded policy with key access is not supported.");

sdk/src/main/java/io/opentdf/platform/sdk/SDK.java

@@ -166,7 +166,7 @@ public static Manifest readManifest(SeekableByteChannel tdfBytes) throws SDKExce
  * to get the {@link Manifest} from a TDF.
  * @param manifest The {@link Manifest} containing the policy.
  * @return The decoded {@link PolicyObject}.
- * @throws SDKException if there is an error during decoding.
+ * @throws {@link SDKException} if there is an error during decoding.
  */
  public static PolicyObject decodePolicyObject(Manifest manifest) throws SDKException {
  return Manifest.decodePolicyObject(manifest);
@@ -176,6 +176,15 @@ public String getPlatformUrl() {
  return platformUrl;
  }
 
+ /**
+ * Indicates that the TDF is malformed in some way
+ */
+ public static class MalformedTDFException extends SDKException {
+ public MalformedTDFException(String errorMessage) {
+ super(errorMessage);
+ }
+ }
+
  /**
  * {@link SplitKeyException} is thrown when the SDK encounters an error related to
  * the inability to reconstruct a split key during decryption.

sdk/src/test/java/io/opentdf/platform/sdk/PolicyInfoTest.java

@@ -2,6 +2,13 @@
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+
+import java.math.BigInteger;
+import java.nio.ByteBuffer;
+import java.util.Arrays;
+import java.util.Random;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
 import static org.junit.jupiter.api.Assertions.*;
 
 class PolicyInfoTest {
@@ -58,4 +65,78 @@ void settingAndGettingPolicyBinding() {
  policyInfo.setPolicyBinding(binding);
  assertArrayEquals(binding, policyInfo.getPolicyBinding());
  }
+
+
+ BigInteger getRandomBigInteger(Random rand, int byteLength) {
+ return new BigInteger((1+rand.nextInt(byteLength-1))*8, rand);
+ }
+
+ @Test
+ void testReadingSignatureWithComponentSizes() {
+ var rand = new Random();
+ var curve = NanoTDFType.ECCurve.SECP256R1;
+ for (var i = 0; i < 100; i++) {
+ var rBytes = getRandomBigInteger(rand, curve.getKeySize()).toByteArray();
+ var sBytes = getRandomBigInteger(rand, curve.getKeySize()) .toByteArray();
+ var buffer = ByteBuffer.allocate(rBytes.length + sBytes.length + 2);
+ buffer.put((byte)rBytes.length);
+ buffer.put(rBytes);
+ buffer.put((byte) sBytes.length);
+ buffer.put(sBytes);
+
+ var originalSig = Arrays.copyOf(buffer.array(), buffer.position());
+
+ buffer.flip();
+
+ ECCMode eccMode = new ECCMode();
+ eccMode.setECDSABinding(true);
+ eccMode.setEllipticCurve(curve);
+
+ byte[] signature = PolicyInfo.readBinding(buffer, eccMode);
+ assertThat(signature).containsExactly(originalSig);
+ // make sure we read all bytes so that reading continues after us in the TDF
+ assertThat(buffer.position()).isEqualTo(buffer.capacity());
+ }
+ }
+
+ @Test
+ void testParsingTooBigSignatureComponents() {
+ {
+ var rand = new Random();
+ var curve = NanoTDFType.ECCurve.SECP256R1;
+ var rBytes = new BigInteger((curve.getKeySize() + 1) * 8, rand).toByteArray();
+ var sBytes = getRandomBigInteger(rand, curve.getKeySize()).toByteArray();
+ var buffer = ByteBuffer.allocate(rBytes.length + sBytes.length + 2);
+ buffer.put((byte) rBytes.length);
+ buffer.put(rBytes);
+ buffer.put((byte) sBytes.length);
+ buffer.put(sBytes);
+
+ buffer.flip();
+
+ ECCMode eccMode = new ECCMode();
+ eccMode.setECDSABinding(true);
+ eccMode.setEllipticCurve(curve);
+ assertThrows(SDK.MalformedTDFException.class, () -> PolicyInfo.readBinding(buffer, eccMode));
+ }
+
+ {
+ var rand = new Random();
+ var curve = NanoTDFType.ECCurve.SECP256R1;
+ var rBytes = getRandomBigInteger(rand, curve.getKeySize()).toByteArray();
+ var sBytes = new BigInteger((curve.getKeySize() + 1) * 8, rand).toByteArray();
+ var buffer = ByteBuffer.allocate(rBytes.length + sBytes.length + 2);
+ buffer.put((byte) rBytes.length);
+ buffer.put(rBytes);
+ buffer.put((byte) sBytes.length);
+ buffer.put(sBytes);
+
+ buffer.flip();
+
+ ECCMode eccMode = new ECCMode();
+ eccMode.setECDSABinding(true);
+ eccMode.setEllipticCurve(curve);
+ assertThrows(SDK.MalformedTDFException.class, () -> PolicyInfo.readBinding(buffer, eccMode));
+ }
+ }
 }