1 files changed, 16 insertions, 0 deletions
diff --git a/dns/tsig.py b/dns/tsig.py
index 6e97dce..2dd4b42 100644
--- a/dns/tsig.py
+++ b/dns/tsig.py
@@ -221,3 +221,19 @@ def get_algorithm(algorithm):
     except KeyError:
         raise NotImplementedError("TSIG algorithm " + str(algorithm) +
                                   " is not supported")
+
+def get_algorithm_and_mac(wire, tsig_rdata, tsig_rdlen):
+    """Return the tsig algorithm for the specified tsig_rdata
+    @raises FormError: The TSIG is badly formed.
+    """
+    current = tsig_rdata
+    (aname, used) = dns.name.from_wire(wire, current)
+    current = current + used
+    (upper_time, lower_time, fudge, mac_size) = \
+                 struct.unpack("!HIHH", wire[current:current + 10])
+    current += 10
+    mac = wire[current:current + mac_size]
+    current += mac_size
+    if current > tsig_rdata + tsig_rdlen:
+        raise dns.exception.FormError
+    return (aname, mac)