Add validation and tests for discriminant_size_bits parameter

src/create_discriminant.h

@@ -4,6 +4,37 @@
 #include "proof_common.h"
 
 integer CreateDiscriminant(std::vector<uint8_t>& seed, int length = 1024) {
+    // INPUT VALIDATION - Fix for issue #282
+
+    // Check 1: Validate discriminant_size_bits is positive
+    if (length <= 0) {
+        throw std::invalid_argument(
+            "discriminant_size_bits must be positive (got " + 
+            std::to_string(length) + ")"
+        );
+    }
+
+    // Check 2: Validate upper bound (optional but recommended)
+    const int MAX_DISCRIMINANT_SIZE_BITS = 16384;
+    if (length > MAX_DISCRIMINANT_SIZE_BITS) {
+        throw std::invalid_argument(
+            "discriminant_size_bits exceeds maximum allowed value"
+        );
+    }
+
+    // Check 3: Validate that length is a multiple of 8 (required by HashPrime)
+    if (length % 8 != 0) {
+        throw std::invalid_argument(
+            "discriminant_size_bits must be a multiple of 8 (got " + 
+            std::to_string(length) + ")"
+        );
+    }
+
+    // Check 4: Validate seed is not empty
+    if (seed.empty()) {
+        throw std::invalid_argument("seed cannot be empty");
+    }
+
     return HashPrime(seed, length, {0, 1, 2, length - 1}) * integer(-1);
 }
 

tests/test_discriminant_validation.py

@@ -0,0 +1,34 @@
+import secrets
+import pytest
+
+from chiavdf import create_discriminant
+
+
+def test_discriminant_size_bits_negative():
+    """Test that discriminant_size_bits of -1 fails"""
+    discriminant_challenge = secrets.token_bytes(10)
+    with pytest.raises(ValueError, match="discriminant_size_bits must be positive"):
+        create_discriminant(discriminant_challenge, -1)
+
+
+def test_discriminant_size_bits_zero():
+    """Test that discriminant_size_bits of 0 fails"""
+    discriminant_challenge = secrets.token_bytes(10)
+    with pytest.raises(ValueError, match="discriminant_size_bits must be positive"):
+        create_discriminant(discriminant_challenge, 0)
+
+
+def test_discriminant_size_bits_too_large():
+    """Test that discriminant_size_bits of 16400 fails (exceeds max of 16384)"""
+    discriminant_challenge = secrets.token_bytes(10)
+    with pytest.raises(ValueError, match="discriminant_size_bits exceeds maximum allowed value"):
+        create_discriminant(discriminant_challenge, 16400)
+
+
+def test_discriminant_size_bits_valid():
+    """Test that discriminant_size_bits of 1024 succeeds"""
+    discriminant_challenge = secrets.token_bytes(10)
+    discriminant = create_discriminant(discriminant_challenge, 1024)
+    # If we get here without an exception, the test passes
+    assert discriminant is not None
+    assert len(discriminant) > 0  # Should return a string representation of the discriminant