Reference no: EM132422100

BIT112 - Mathematics for IT - Melbourne Polytechnic

Task: Explore how Public Key Cryptography works.

Using your Student ID, generate two primes and encrypt your student ID with your own Private Key.

Use the Wiener attack to break your private key and is this way steal your identity by using your private key to encode another number and masquerade as you.

Making your own Keys:

(i) Explore how Public Key Cryptography works and summarise this in your own words with particular attention to how the method generates these keys.

(ii) From your exploration above, generate Private and Public Keys using your student ID.

(iii) Using your student ID, determine how bits the number part can be represented with.

(iv) For a particular number of binary bits determine the number of prime numbers available in that bit range.

(v) (a) Using the Wolframalpha "nextprime" function and your student ID create two prime numbers which are of the form 4x+1. Such that P₁ =4x₁+1 and P₂=4x₂+1.

(b) Check that they have the same number of binary bits.

(vi) (a)Using the Wolframalpha "nextprime" function and your student ID create two prime numbers which are of the form 4x+3. Such that P₃ =4x₃+3 and P₄=4x₄+3.

(b) Check that they have the same number of binary bits.

(vii) (a) Use P₁ and P₂ to generate your public keys and encrypt your student ID.

(b) Use P₃ and P₄ to generate your public keys and encrypt your student ID.

(viii) Create a private key and use this to decrypt and recover your student ID.

Breaking the Keys:

(i) Express P₁ and P₂ as the sum of two squares (for example 5=1² +2²).

Draw these as two right angle triangles (a,b,c). Note that c₁ = √(P₁ ) , c₂ = √(P₂)

(a) Using the equations below:

Let P₁ = C₁ and P₂ = C₂ and let the smallest value of the two squares be nexpress the sides of each triangle as:

c = n² + (n+2m-1)² b = 2n(n+2m-1) a=(2m-1)(2m+2n-1)

(b) Test that both your triangle solutions meet the condition that: c² = a² + b². Represent this geometrically.

(c) Multiply P₁ and P₂ together: N=P₁P₂. Can N be expressed as the sum of two squares? Does this correspond to part 2(iii)(a).

(d) Using Euler's factorization method, show how the original prime numbers can be recovered using the sum of squares method.
Can P₃ and P₄ be represented as the sum of two squares?

Can N:N= P₃ P₄ be expressed as the sum of two squares as in (iii)(c)? Can Euler's Factorization now be used? Why?

For Primes,P1 and P2 , subtract 1 and multiply these together: φ(n)=(P₁-1)(P₂-1)

Show that if φ(n) and N are known, that the original primes P1and P2 can be recovered.

Using your public key, show how your private keys can be recovered using the Wiener attack by recovering P₁ and P₂.

As the villain, armed with this information andmasquerading as you, send a different encrypted Student ID (not yours) encrypted with the recovered key. Use the same public key as earlier to recover the masquerading Student ID.

Final Report:

Your final report is a professional representation of parts (1) and (2) above, drawing on the relevant literature (including journals) where relevant and properly referencing these. You should also look at linkages between parts (1) and (2) and explore the structures of primes with particular attention to why primes of the type 4x+1 are weaker than 4x+3.