Update DiffieHellman.java

Author: riti2601

src/main/java/com/thealgorithms/ciphers/DiffieHellman.java

@@ -10,6 +10,10 @@ public final class DiffieHellman {
 
     // Constructor to initialize base, secret, and prime
     public DiffieHellman(BigInteger base, BigInteger secret, BigInteger prime) {
+        // Check for non-null and positive values
+        if (base == null || secret == null || prime == null || base.signum() <= 0 || secret.signum() <= 0 || prime.signum() <= 0) {
+            throw new IllegalArgumentException("Base, secret, and prime must be non-null and positive values.");
+        }
         this.base = base;
         this.secret = secret;
         this.prime = prime;
@@ -23,16 +27,27 @@ public BigInteger calculatePublicValue() {
 
     // Method to calculate the shared secret key (otherPublic^secret mod p)
     public BigInteger calculateSharedSecret(BigInteger otherPublicValue) {
+        if (otherPublicValue == null || otherPublicValue.signum() <= 0) {
+            throw new IllegalArgumentException("Other public value must be non-null and positive.");
+        }
         // Returns b^x mod p or a^y mod p
         return otherPublicValue.modPow(secret, prime);
     }
 
     // Static utility methods for direct calculation (if needed)
     public static BigInteger calculatePublicValue(BigInteger base, BigInteger secret, BigInteger prime) {
+        // Check for valid inputs
+        if (base == null || secret == null || prime == null || base.signum() <= 0 || secret.signum() <= 0 || prime.signum() <= 0) {
+            throw new IllegalArgumentException("Base, secret, and prime must be non-null and positive values.");
+        }
         return base.modPow(secret, prime);
     }
 
     public static BigInteger calculateSharedSecret(BigInteger otherPublicValue, BigInteger secret, BigInteger prime) {
+        // Check for valid inputs
+        if (otherPublicValue == null || secret == null || prime == null || otherPublicValue.signum() <= 0 || secret.signum() <= 0 || prime.signum() <= 0) {
+            throw new IllegalArgumentException("Other public value, secret, and prime must be non-null and positive values.");
+        }
         return otherPublicValue.modPow(secret, prime);
     }
 }