IMPLEMENTAZIONE DELL'ALGORITMO DI DIFFIE-HELLMAN

Algoritmo di Diffie-Hellman:

L'algoritmo Diffie-Hellman viene utilizzato per stabilire un segreto condiviso che può essere utilizzato per comunicazioni segrete durante lo scambio di dati su una rete pubblica utilizzando la curva ellittica per generare punti e ottenere la chiave segreta utilizzando i parametri.

Per semplicità e implementazione pratica dell'algoritmo considereremo solo 4 variabili una prima P e G (una radice primitiva di P) e due valori privati a e b.
P e G sono entrambi numeri disponibili al pubblico. Gli utenti (ad esempio Alice e Bob) scelgono i valori privati aeb, generano una chiave e la scambiano pubblicamente. La persona opposta riceve la chiave e genera una chiave segreta dopo la quale ha la stessa chiave segreta da crittografare.

La spiegazione passo passo è la seguente:

Alice	Bob
Chiavi pubbliche disponibili = PG	Chiavi pubbliche disponibili = PG
Chiave privata selezionata = a	Chiave privata selezionata = b
Chiave generata = x = G^a mod P	Chiave generata = y = G^b mod P
Ha luogo lo scambio delle chiavi generate
Chiave ricevuta = y	chiave ricevuta = x
Chiave segreta generata = k_a = y^a mod P	Chiave segreta generata = k_b = x^b mod P
Algebricamente si può dimostrare che k_a = k_b
Gli utenti ora hanno una chiave segreta simmetrica da crittografare

Esempio:

Step 1: Alice and Bob get public numbers P = 23 G = 9  
Step 2: Alice selected a private key a = 4 and  
 Bob selected a private key b = 3  
Step 3: Alice and Bob compute public values  
Alice: x =(9^4 mod 23) = (6561 mod 23) = 6  
 Bob: y = (9^3 mod 23) = (729 mod 23) = 16  
Step 4: Alice and Bob exchange public numbers  
Step 5: Alice receives public key y =16 and  
 Bob receives public key x = 6  
Step 6: Alice and Bob compute symmetric keys  
 Alice: ka = y^a mod p = 65536 mod 23 = 9  
 Bob: kb = x^b mod p = 216 mod 23 = 9  
Step 7: 9 is the shared secret.

Attuazione:

C++

/* This program calculates the Key for two persons using the Diffie-Hellman Key exchange algorithm using C++ */ #include  #include    using namespace std; // Power function to return value of a ^ b mod P long long int power(long long int a long long int b  long long int P) {  if (b == 1)  return a;  else  return (((long long int)pow(a b)) % P); } // Driver program int main() {  long long int P G x a y b ka kb;  // Both the persons will be agreed upon the  // public keys G and P  P = 23; // A prime number P is taken  cout << 'The value of P : ' << P << endl;  G = 9; // A primitive root for P G is taken  cout << 'The value of G : ' << G << endl;  // Alice will choose the private key a  a = 4; // a is the chosen private key  cout << 'The private key a for Alice : ' << a << endl;  x = power(G a P); // gets the generated key  // Bob will choose the private key b  b = 3; // b is the chosen private key  cout << 'The private key b for Bob : ' << b << endl;  y = power(G b P); // gets the generated key  // Generating the secret key after the exchange  // of keys  ka = power(y a P); // Secret key for Alice  kb = power(x b P); // Secret key for Bob  cout << 'Secret key for the Alice is : ' << ka << endl;  cout << 'Secret key for the Bob is : ' << kb << endl;  return 0; } // This code is contributed by Pranay Arora

/* This program calculates the Key for two persons using the Diffie-Hellman Key exchange algorithm */ #include  #include  // Power function to return value of a ^ b mod P long long int power(long long int a long long int b  long long int P) {  if (b == 1)  return a;  else  return (((long long int)pow(a b)) % P); } // Driver program int main() {  long long int P G x a y b ka kb;  // Both the persons will be agreed upon the  // public keys G and P  P = 23; // A prime number P is taken  printf('The value of P : %lldn' P);  G = 9; // A primitive root for P G is taken  printf('The value of G : %lldnn' G);  // Alice will choose the private key a  a = 4; // a is the chosen private key  printf('The private key a for Alice : %lldn' a);  x = power(G a P); // gets the generated key  // Bob will choose the private key b  b = 3; // b is the chosen private key  printf('The private key b for Bob : %lldnn' b);  y = power(G b P); // gets the generated key  // Generating the secret key after the exchange  // of keys  ka = power(y a P); // Secret key for Alice  kb = power(x b P); // Secret key for Bob  printf('Secret key for the Alice is : %lldn' ka);  printf('Secret Key for the Bob is : %lldn' kb);  return 0; }

Java

// This program calculates the Key for two persons // using the Diffie-Hellman Key exchange algorithm class GFG {  // Power function to return value of a ^ b mod P  private static long power(long a long b long p)  {  if (b == 1)  return a;  else  return (((long)Math.pow(a b)) % p);  }  // Driver code  public static void main(String[] args)  {  long P G x a y b ka kb;  // Both the persons will be agreed upon the  // public keys G and P  // A prime number P is taken  P = 23;  System.out.println('The value of P:' + P);  // A primitive root for P G is taken  G = 9;  System.out.println('The value of G:' + G);  // Alice will choose the private key a  // a is the chosen private key  a = 4;  System.out.println('The private key a for Alice:'  + a);  // Gets the generated key  x = power(G a P);  // Bob will choose the private key b  // b is the chosen private key  b = 3;  System.out.println('The private key b for Bob:'  + b);  // Gets the generated key  y = power(G b P);  // Generating the secret key after the exchange  // of keys  ka = power(y a P); // Secret key for Alice  kb = power(x b P); // Secret key for Bob  System.out.println('Secret key for the Alice is:'  + ka);  System.out.println('Secret key for the Bob is:'  + kb);  } } // This code is contributed by raghav14

Python

# Diffie-Hellman Code # Power function to return value of a^b mod P def power(a b p): if b == 1: return a else: return pow(a b) % p # Main function def main(): # Both persons agree upon the public keys G and P # A prime number P is taken P = 23 print('The value of P:' P) # A primitive root for P G is taken G = 9 print('The value of G:' G) # Alice chooses the private key a # a is the chosen private key a = 4 print('The private key a for Alice:' a) # Gets the generated key x = power(G a P) # Bob chooses the private key b # b is the chosen private key b = 3 print('The private key b for Bob:' b) # Gets the generated key y = power(G b P) # Generating the secret key after the exchange of keys ka = power(y a P) # Secret key for Alice kb = power(x b P) # Secret key for Bob print('Secret key for Alice is:' ka) print('Secret key for Bob is:' kb) if __name__ == '__main__': main()

// C# implementation to calculate the Key for two persons // using the Diffie-Hellman Key exchange algorithm using System; class GFG {  // Power function to return value of a ^ b mod P  private static long power(long a long b long P)  {  if (b == 1)  return a;  else  return (((long)Math.Pow(a b)) % P);  }  public static void Main()  {  long P G x a y b ka kb;  // Both the persons will be agreed upon the  // public keys G and P  P = 23; // A prime number P is taken  Console.WriteLine('The value of P:' + P);  G = 9; // A primitive root for P G is taken  Console.WriteLine('The value of G:' + G);  // Alice will choose the private key a  a = 4; // a is the chosen private key  Console.WriteLine('nThe private key a for Alice:'  + a);  x = power(G a P); // gets the generated key  // Bob will choose the private key b  b = 3; // b is the chosen private key  Console.WriteLine('The private key b for Bob:' + b);  y = power(G b P); // gets the generated key  // Generating the secret key after the exchange  // of keys  ka = power(y a P); // Secret key for Alice  kb = power(x b P); // Secret key for Bob  Console.WriteLine('nSecret key for the Alice is:'  + ka);  Console.WriteLine('Secret key for the Alice is:'  + kb);  } } // This code is contributed by Pranay Arora

JavaScript

<script> // This program calculates the Key for two persons // using the Diffie-Hellman Key exchange algorithm  // Power function to return value of a ^ b mod P function power(a b p)  {  if (b == 1)  return a;  else  return((Math.pow(a b)) % p); } // Driver code var P G x a y b ka kb; // Both the persons will be agreed upon the // public keys G and P // A prime number P is taken P = 23; document.write('The value of P:' + P + '  
'); // A primitive root for P G is taken G = 9; document.write('The value of G:' + G + '  
'); // Alice will choose the private key a // a is the chosen private key a = 4;  document.write('The private key a for Alice:' +   a + '  
'); // Gets the generated key x = power(G a P); // Bob will choose the private key b // b is the chosen private key  b = 3;  document.write('The private key b for Bob:' +  b + '  
'); // Gets the generated key y = power(G b P);  // Generating the secret key after the exchange // of keys ka = power(y a P); // Secret key for Alice kb = power(x b P); // Secret key for Bob document.write('Secret key for the Alice is:' +   ka + '  
'); document.write('Secret key for the Bob is:' +   kb + '  
'); // This code is contributed by Ankita saini </script>

Produzione

The value of P : 23 The value of G : 9 The private key a for Alice : 4 The private key b for Bob : 3 Secret key for the Alice is : 9 Secret key for the Bob is : 9

TechCodeview

Implementazione dell'algoritmo di Diffie-Hellman

Algoritmo di Diffie-Hellman: