Diffie-Hellman-and-Encryption-Project (CSE 539)

Create a 256-bit shared key by simulating a Diffie-Hellman key exchange and perform encryption and decryption of sample cipher and plain texts

Directions

The first part of this assignment involves the creation of a 256-bit key for performing encryption. You will be implementing the Diffie-Hellman key exchange protocol. Typically, this protocol involves two parties concurrently sharing values and generating a key. In this assignment, you will be given all necessary values immediately and will not be required to send values over any channel. In this way, you can perform calculations as a single party.

Here is a brief reminder of how Diffie-Hellman works:

1. Alice and Bob agree on values for g and N.
2. Alice randomly picks x and Bob randomly picks y.
3. Alice computes g^x mod N and sends it to Bob (call this gx).
4. Bob computes g^y mod N and sends it to Alice (call this gy).
5. Alice computes (gy)^x mod N, and Bob computes (gx)^y mod N. These two values are equivalent and are the key.

The encryption algorithm you will be using in this project is AES (i.e., Rijndael encryption). You can use the AES class in the C# System.Security.Cryptography namespace. You will be using the 256-bit key mode. In order to perform the encryption, you will also need an IV. In this exercise, you will employ a 128-bit IV passed via command line in hex. Here is the list of values you will receive from the command line arguments, in order:

1. 128-bit IV in hex
2. g_e in base 10
3. g_c in base 10
4. N_e in base 10
5. N_c in base 10
6. x in base 10
7. g y mod N in base 10
8. An encrypted message C in hex
9. A plaintext message P as a string

After calculating the key, your program must perform a decryption of the given ciphertext bytes and an encryption of the given plaintext string. Your program should output these values as a comma separated pair (the decrypted text followed by the encrypted bytes). Here is a full example:

$ dotnet run "A2 2D 93 61 7F DC 0D 8E C6 3E A7 74 51 1B 24 B2" 251 465 255 1311 2101864342 8995936589171851885163650660432521853327227178155593274584417851704581358902 "F2 2C 95 FC 6B 98 BE 40 AE AD 9C 07 20 3B B3 9F F8 2F 6D 2D 69 D6 5D 40 0A 75 45 80 45 F2 DE C8 6E C0 FF 33 A4 97 8A AF 4A CD 6E 50 86 AA 3E DF" AfYw7Z6RzU9ZaGUloPhH3QpfA1AXWxnCGAXAwk3f6MoTx

uUNX8P03U3J91XsjCqOJ0LVqt4I4B2ZqEBfX1gCGBH4hH,3D E9 B7 31 42 D7 54 D8 96 12 C9 97 01 12 78 F7 A2 4F 69 1A FF F4 42 99 13 A1 BD 73 52 E5 48 63 33 7A 39 BF C5 25 AD 53 26 53 0D E4 81 51 D1 3E