convert signature to DER format (java expects this)

lbalmaceda · lbalmaceda · commit 72704dd0236f · 2016-11-04T18:47:51.000-03:00
diff --git a/lib/src/main/java/com/auth0/jwtdecodejava/algorithms/Algorithm.java b/lib/src/main/java/com/auth0/jwtdecodejava/algorithms/Algorithm.java
@@ -79,7 +79,7 @@ public static Algorithm HMAC512(String secret) {
      * @return a valid ECDSA256 Algorithm.
      */
     public static Algorithm ECDSA256(PublicKey publicKey) {
-        return new ECDSAAlgorithm("ES256", "SHA256withECDSA", publicKey);
+        return new ECDSAAlgorithm("ES256", "SHA256withECDSA", 32, publicKey);
     }
 
     /**
@@ -89,7 +89,7 @@ public static Algorithm ECDSA256(PublicKey publicKey) {
      * @return a valid ECDSA384 Algorithm.
      */
     public static Algorithm ECDSA384(PublicKey publicKey) {
-        return new ECDSAAlgorithm("ES384", "SHA384withECDSA", publicKey);
+        return new ECDSAAlgorithm("ES384", "SHA384withECDSA", 48, publicKey);
     }
 
     /**
@@ -99,7 +99,7 @@ public static Algorithm ECDSA384(PublicKey publicKey) {
      * @return a valid ECDSA512 Algorithm.
      */
     public static Algorithm ECDSA512(PublicKey publicKey) {
-        return new ECDSAAlgorithm("ES512", "SHA512withECDSA", publicKey);
+        return new ECDSAAlgorithm("ES512", "SHA512withECDSA", 66, publicKey);
     }
 
     public static Algorithm none() {
diff --git a/lib/src/main/java/com/auth0/jwtdecodejava/algorithms/ECDSAAlgorithm.java b/lib/src/main/java/com/auth0/jwtdecodejava/algorithms/ECDSAAlgorithm.java
@@ -7,13 +7,15 @@
 
 class ECDSAAlgorithm extends Algorithm {
 
+    private final int ecNumberSize;
     private final PublicKey publicKey;
 
-    ECDSAAlgorithm(String id, String algorithm, PublicKey publicKey) {
+    ECDSAAlgorithm(String id, String algorithm, int ecNumberSize, PublicKey publicKey) {
         super(id, algorithm);
         if (publicKey == null) {
             throw new IllegalArgumentException("The PublicKey cannot be null");
         }
+        this.ecNumberSize = ecNumberSize;
         this.publicKey = publicKey;
     }
 
@@ -29,6 +31,9 @@ public void verify(String[] jwtParts) throws SignatureVerificationException {
             s.initVerify(publicKey);
             s.update(content.getBytes());
             byte[] signature = Base64.decodeBase64(jwtParts[2]);
+            if (isJOSESignature(signature)) {
+                signature = JOSEToDER(signature);
+            }
             boolean valid = s.verify(signature);
             if (!valid) {
                 throw new SignatureVerificationException(this);
@@ -38,4 +43,64 @@ public void verify(String[] jwtParts) throws SignatureVerificationException {
         }
     }
 
+    private boolean isJOSESignature(byte[] signature) {
+        //TODO: Check if the signature has JOSE format.
+        return true;
+    }
+
+    private byte[] JOSEToDER(byte[] joseSignature) throws SignatureException {
+        if (joseSignature.length != ecNumberSize * 2) {
+            throw new SignatureException(String.format("The signature length was invalid. Expected %d bytes but received %d", ecNumberSize * 2, joseSignature.length));
+        }
+
+        // Retrieve R and S number's length and padding.
+        int rPadding = countPadding(joseSignature, 0, ecNumberSize);
+        int sPadding = countPadding(joseSignature, ecNumberSize, joseSignature.length);
+        int rLength = ecNumberSize - rPadding;
+        int sLength = ecNumberSize - sPadding;
+
+        int length = 2 + rLength + 2 + sLength;
+        if (length > 0xFF) {
+            throw new SignatureException("Invalid ECDSA signature format");
+        }
+
+        byte[] derSignature;
+        int offset;
+        if (length > 0x7f) {
+            derSignature = new byte[3 + length];
+            derSignature[1] = (byte) 0x81;
+            offset = 2;
+        } else {
+            derSignature = new byte[2 + length];
+            offset = 1;
+        }
+
+        // DER Structure: http://crypto.stackexchange.com/a/1797
+        // Header with length info
+        derSignature[0] = (byte) 0x30;
+        derSignature[offset++] = (byte) length;
+        derSignature[offset++] = (byte) 0x02;
+        derSignature[offset++] = (byte) rLength;
+
+        // R number
+        System.arraycopy(joseSignature, 0, derSignature, offset + (rLength - ecNumberSize), ecNumberSize);
+        offset += rLength;
+
+        // S number length
+        derSignature[offset++] = (byte) 0x02;
+        derSignature[offset++] = (byte) sLength;
+
+        // S number
+        System.arraycopy(joseSignature, ecNumberSize, derSignature, offset + (sLength - ecNumberSize), ecNumberSize);
+
+        return derSignature;
+    }
+
+    private int countPadding(byte[] bytes, int fromIndex, int toIndex) {
+        int padding = 0;
+        while (fromIndex + padding < toIndex && bytes[fromIndex + padding] == 0) {
+            padding++;
+        }
+        return bytes[fromIndex + padding] > 0x7f ? padding : padding - 1;
+    }
 }
