add implementation of poly1305 pure python

by Hubert Kario, LGPLv2.1 licensed

diff --git a/src/openpower/decoder/isa/poly1305.py b/src/openpower/decoder/isa/poly1305.py
new file mode 100644 (file)
index 0000000..8341159
--- /dev/null
+++ b/src/openpower/decoder/isa/poly1305.py
@@ -0,0 +1,48 @@
+# Copyright (c) 2015, Hubert Kario
+# License: LGPLv2.1
+"""Implementation of Poly1305 authenticator for RFC 7539"""
+
+def divceil(a, b): return -(a // -b)
+
+class Poly1305(object):
+
+    """Poly1305 authenticator"""
+
+    P = 0x3fffffffffffffffffffffffffffffffb # 2^130-5
+
+    @staticmethod
+    def le_bytes_to_num(data):
+        """Convert a number from little endian byte format"""
+        ret = 0
+        for i in range(len(data) - 1, -1, -1):
+            ret <<= 8
+            ret += data[i]
+        return ret
+
+    @staticmethod
+    def num_to_16_le_bytes(num):
+        """Convert number to 16 bytes in little endian format"""
+        ret = [0]*16
+        for i, _ in enumerate(ret):
+            ret[i] = num & 0xff
+            num >>= 8
+        return bytearray(ret)
+
+    def __init__(self, key):
+        """Set the authenticator key"""
+        if len(key) != 32:
+            raise ValueError("Key must be 256 bit long")
+        self.acc = 0
+        self.r = self.le_bytes_to_num(key[0:16])
+        self.r &= 0x0ffffffc0ffffffc0ffffffc0fffffff
+        self.s = self.le_bytes_to_num(key[16:32])
+
+    def create_tag(self, data):
+        """Calculate authentication tag for data"""
+        for i in range(0, divceil(len(data), 16)):
+            n = self.le_bytes_to_num(data[i*16:(i+1)*16] + b'\x01')
+            self.acc += n
+            self.acc = (self.r * self.acc) % self.P
+        self.acc += self.s
+        return self.num_to_16_le_bytes(self.acc)
+