Added python-only implementation of PKCS7 padding

RNS/Cryptography/PKCS7.py

@@ -0,0 +1,18 @@
+class PKCS7:
+    BLOCKSIZE = 16
+
+    @staticmethod
+    def pad(data, bs=BLOCKSIZE):
+        l = len(data)
+        n = bs-l%bs
+        v = bytes([n])
+        return data+v*n
+
+    @staticmethod
+    def unpad(data, bs=BLOCKSIZE):
+        l = len(data)
+        n = data[-1]
+        if n > bs:
+            raise ValueError("Cannot unpad, invalid padding length of "+str(n)+" bytes")
+        else:
+            return data[:l-n]