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diff --git a/src/model/python/modexp.py b/src/model/python/modexp.py
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+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+#=======================================================================
+#
+# modexp.py
+# ---------
+# A python model for doing modular exponention.
+#
+#
+# Author: Joachim Strömbergson
+# Copyright (c) 2014, Secworks Sweden AB
+#
+# Redistribution and use in source and binary forms, with or
+# without modification, are permitted provided that the following
+# conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+#
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in
+#    the documentation and/or other materials provided with the
+#    distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+# COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+# STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+# ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
+#=======================================================================
+
+#-------------------------------------------------------------------
+# Python module imports.
+#-------------------------------------------------------------------
+import sys
+
+
+#-------------------------------------------------------------------
+# Defines.
+#-------------------------------------------------------------------
+VERBOSE = False
+
+
+#-------------------------------------------------------------------
+# iter_mult()
+#
+# Iterative multiplier (i*j) with operands that are bitlen
+# number of bits.
+#-------------------------------------------------------------------
+def iter_mult(i, j, bitlen):
+    print("Mult of 0x%08x and 0x%08x of max 0x%08x bits" %
+          (i, j, bitlen))
+
+    r = 0
+    max = 2**bitlen - 1
+
+    for bit in range(bitlen):
+        mask = ((j & (1 << bit)))
+        r = (r + (i * mask)) & max
+        print("bit: 0x%08x, mask = 0x%01x, r = 0x%08x" %
+              (bit, mask, r))
+    return r
+
+
+#-------------------------------------------------------------------
+# iter_exp()
+#
+# Iterative exponentiator (i ** j) with operands that are
+# bitlen number of bits.
+#-------------------------------------------------------------------
+def iter_exp(i, j, bitlen):
+    print("Exp of 0x%08x and 0x%08x of max 0x%08x bits" %
+          (i, j, bitlen))
+
+    n = i
+    for bit in range(j):
+        n = iter_mult(n, n, bitlen)
+    return n
+
+
+#-------------------------------------------------------------------
+# gen_keypair()
+#
+# Generate a keypair (and exponent) with n bits in length.
+#-------------------------------------------------------------------
+def gen_keypair(bitlen):
+    print("Generating keys with %d bits" % (bitlen))
+    print("")
+
+    e = 3
+    pub = 2**bitlen - 1
+    priv = pub - 2
+
+    return (pub, priv, e)
+
+
+#-------------------------------------------------------------------
+# keytest()
+#-------------------------------------------------------------------
+def keytest():
+    print("key encryption and decryption")
+    print("-----------------------------")
+
+    p = 11
+    q = 13
+    n = p * q
+    tiotent = (p - 1) * (q - 1)
+
+    print("p = %d, q = %d, n = %d, tiotent = %d" % (p, q, n, tiotent))
+
+    e = 7
+    d = 103
+
+    print("e = %d, d = %d" % (e, d))
+
+    print("Public key: e, n = %d, %d" % (e, n))
+    print("private key: d = %d" % (d))
+
+    m = 9
+    cm = modexp(m, e, n)
+    m2 = modexp(cm, d, n)
+    print("Encryption of message m  = %d -> cm = %d" % (m, cm))
+    print("Decryption of message cm = %d -> m  = %d" % (cm, m2))
+
+
+#-------------------------------------------------------------------
+# modtest()
+#-------------------------------------------------------------------
+def modtest():
+    print("modular exponentition")
+    print("---------------------")
+
+    M = 12345
+    e = 3
+    N = 12347
+
+    print("M = %d, e = %d, N = %d" % (M, e, N))
+    print(modexp(M, e, N))
+    print("")
+
+    M = 2**8192 - 37
+    e = 3
+    N = 2**8192 - 1
+
+    print("M = %d, e = %d, N = %d" % (M, e, N))
+    print(modexp(M, e, N))
+    print("")
+
+
+#-------------------------------------------------------------------
+# modexp()
+#
+# Perform generic modular exponention of the given message M
+# using the exponent e and modulus N.
+#-------------------------------------------------------------------
+def modexp(M, e, N):
+    return (M ** e) % N
+
+
+#-------------------------------------------------------------------
+# main()
+#
+# Parse any arguments and run the tests.
+#-------------------------------------------------------------------
+def main():
+#    my_keypair = gen_keypair(12)
+#    print(my_keypair)
+#    modtest()
+#    keytest()
+
+    # test of iterative multiply.
+    print(iter_mult(2, 3, 4))
+    print(iter_mult(2, 3, 5))
+    print(iter_mult(2543, 1201, 12))
+    print(iter_mult(2543, 1201, 16))
+    print(iter_mult(2543, 1201, 23))
+
+    # test of iterative exponentiation.
+    print(iter_exp(2, 3, 12))
+    print(iter_exp(8, 8, 4))
+
+
+#-------------------------------------------------------------------
+# __name__
+# Python thingy which allows the file to be run standalone as
+# well as parsed from within a Python interpreter.
+#-------------------------------------------------------------------
+if __name__=="__main__":
+    # Run the main function.
+    sys.exit(main())
+
+
+#=======================================================================
+# EOF modexp.py
+#=======================================================================