Merge pull request #204 from pongpet-licel/master

Fixed CRC32 calculation to reflect input and result
licel · Mar 13, 2023 · b54b18b · b54b18b
2 parents fa9d42e + f8113c1
commit b54b18b
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Showing 2 changed files with 24 additions and 4 deletions.
diff --git a/src/main/java/com/licel/jcardsim/crypto/CRC32.java b/src/main/java/com/licel/jcardsim/crypto/CRC32.java
@@ -72,7 +72,7 @@ private void crc32(byte inBuf[], short inOff, short inLen) {
         short poly_l = Util.getShort(polynom, (short) 2);
         byte carry = 0;
         for (short i = inOff; i < (short) (inOff + inLen); i++) {
-            short d_h = (short) (inBuf[i] << 8);
+            short d_h = (short) (reflect8(inBuf[i]) << 8);
             for (short k = 0; k < 8; k++) {
                 if (((fcs_h ^ d_h) & 0x8000) != 0) {
                     carry = 0;
@@ -104,8 +104,26 @@ private void crc32(byte inBuf[], short inOff, short inLen) {
 
         }
 
-        Util.setShort(crc32, (short) 2, fcs_l);
-        Util.setShort(crc32, (short) 0, fcs_h);
+        Util.setShort(crc32, (short) 2, reflect16(fcs_h));
+        Util.setShort(crc32, (short) 0, reflect16(fcs_l));
+    }
+
+    private byte reflect8(byte input){
+        byte reflected = 0;
+        for( byte i = 0; i < 8; i++){
+            if((input & (0x80 >> i)) > 0 )
+                reflected |= (1 << i);
+        }
+        return reflected;
+    }
+
+    private short reflect16(short input){
+        short reflected = 0;
+        for( byte i = 0; i < 16; i++){
+            if((input & (0x8000 >> i)) > 0 )
+                reflected |= (1 << i);
+        }
+        return reflected;
     }
 
     short shift(short s) {

diff --git a/src/test/java/com/licel/jcardsim/crypto/CRC32Test.java b/src/test/java/com/licel/jcardsim/crypto/CRC32Test.java
@@ -19,6 +19,7 @@
 import junit.framework.TestCase;
 import org.bouncycastle.util.Arrays;
 import org.bouncycastle.util.encoders.Hex;
+import java.util.zip.CRC32;
 
 /**
  * Test for <code>CRC32</code>
@@ -29,7 +30,8 @@ public class CRC32Test extends TestCase {
     // etalon msg
     String MESSAGE = "C46A3D01F5494013F9DFF3C5392C64";
     // etalon crc
-    String CRC = "7C6277D0";
+//    String CRC = "7C6277D0";
+    String CRC = "C6A5A2E4";
 
     public CRC32Test(String testName) {
         super(testName);