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diff --git a/3544/CH2/EX2.56/Ex2_56.sce b/3544/CH2/EX2.56/Ex2_56.sce
new file mode 100644
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+
+//Man-in-the-middle attack in Diffie-Hellman key exchange
+
+n = 11                      //Large prime numbers
+g = 7                       //which are public
+
+printf("n: %d\ng: %d\n",n,g)
+
+x_a = 3                     //Alice's x
+x_t = 8                     //Tom's x
+y_t = 6                     //Tom's y
+y_b = 9                     //Bob's y
+
+A_a = modulo(g^x_a,n)       //Alice's A 
+A_t = modulo(g^x_t,n)       //Tom's A
+B_t = modulo(g^y_t,n)       //Tom's B
+B_b = modulo(g^y_b,n)       //Bob's B
+
+disp("Before intrusion by Tom: ")
+disp("For Alice:")
+printf("x: %d\nA: %d\n",x_a,A_a)
+disp("For Tom:")
+printf("x: %d\ty: %d\nA: %d\tB: %d\n",x_t,y_t,A_t,B_t)
+disp("For Bob:")
+printf("y: %d\nB: %d\n",y_b,B_b)
+
+A_b = A_t                   //Substituting Tom's A as A for Bob
+B_a = B_t                   //Substituting Tom's B as B for Alice 
+A_t = A_a                   //Changing Tom's A to Alice's A
+B_t = B_b                   //Changing Tom's B to Bob's B
+
+disp("After intrusion by Tom during exhange of keys: ")
+disp("For Alice:")
+printf("x: %d\nA: %d\tB: %d\n",x_a,A_a,B_a)
+disp("For Tom:")
+printf("x: %d\ty: %d\nA: %d\tB: %d\n",x_t,y_t,A_t,B_t)
+disp("For Bob:")
+printf("y: %d\nA: %d\tB: %d\n",y_b,A_b,B_b)
+
+
+
+//Now, Tom can calculate separate keys for Alice and Bob
+
+K1_a = modulo(B_a^x_a,n)        //Alice's key
+K1_t = modulo(B_t^x_t,n)        //Tom's key for Bob
+K2_t = modulo(A_t^y_t,n)        //Tom's key for Alice
+K2_b = modulo(A_b^y_b,n)        //Bob's key
+
+printf("\n\nKeys:\n")
+
+disp("Alice''s key:")
+printf("\tK1: %d\n\n",K1_a)
+disp("Tom''s keys:")
+printf("\nTo communicate with Alice\n\tK2: %d",K2_t)
+printf("\nTo communicate with Bob\n\tK1: %d\n\n",K1_t)
+disp("Bob''s key:")
+printf("\tK2: %d",K2_b)
+
+//We can see that K1_a == K2+t and K1_t == K2_b
+//Thus, Tom can communicate with Alice using K2_t and with Bob using K1_t
+//and easily carry out 
+