1 files changed, 13 insertions, 0 deletions
diff --git a/rsa/common.py b/rsa/common.py
index b8f7aa6..7c852b6 100644
--- a/rsa/common.py
+++ b/rsa/common.py
@@ -14,5 +14,18 @@ def bit_size(number):
 
     '''
 
+    if number < 0:
+        raise ValueError('Only nonnegative numbers possible: %s' % number)
+
+    if number == 0:
+        return 1
+    
     return int(math.ceil(math.log(number, 2)))
 
+def byte_size(number):
+    """Returns the number of bytes required to hold a specific long number.
+    
+    The number of bytes is rounded up.
+    """
+
+    return int(math.ceil(bit_size(number) / 8.0))