1 files changed, 50 insertions, 0 deletions
diff --git a/pg/src/main/java/org/spongycastle/openpgp/operator/PGPPad.java b/pg/src/main/java/org/spongycastle/openpgp/operator/PGPPad.java
new file mode 100644
index 00000000..d3ef360c
--- /dev/null
+++ b/pg/src/main/java/org/spongycastle/openpgp/operator/PGPPad.java
@@ -0,0 +1,50 @@
+package org.spongycastle.openpgp.operator;
+
+import org.spongycastle.openpgp.PGPException;
+
+/**
+ * Utility class that provides padding addition and removal for PGP session keys.
+ */
+public class PGPPad
+{
+    private PGPPad()
+    {
+
+    }
+
+    public static byte[] padSessionData(byte[] sessionInfo)
+    {
+        byte[] result = new byte[40];
+
+        System.arraycopy(sessionInfo, 0, result, 0, sessionInfo.length);
+
+        byte padValue = (byte)(result.length - sessionInfo.length);
+
+        for (int i =  sessionInfo.length; i != result.length; i++)
+        {
+            result[i] = padValue;
+        }
+
+        return result;
+    }
+
+    public static byte[] unpadSessionData(byte[] encoded)
+        throws PGPException
+    {
+        byte padValue = encoded[encoded.length - 1];
+
+        for (int i = encoded.length - padValue; i != encoded.length; i++)
+        {
+            if (encoded[i] != padValue)
+            {
+                throw new PGPException("bad padding found in session data");
+            }
+        }
+
+        byte[] taggedKey = new byte[encoded.length - padValue];
+
+        System.arraycopy(encoded, 0, taggedKey, 0, taggedKey.length);
+
+        return taggedKey;
+    }
+}