From fee80dd230e7fba132d03a34f1dd1d6aae0d0281 Mon Sep 17 00:00:00 2001
From: David Hook <dgh@cryptoworkshop.com>
Date: Fri, 22 Dec 2023 15:34:47 +1100
Subject: [PATCH] refactored f2m m check.

---
 .../org/bouncycastle/math/ec/ECCurve.java     | 10 +++++-----
 .../math/ec/test/ECPointTest.java             | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/core/src/main/java/org/bouncycastle/math/ec/ECCurve.java b/core/src/main/java/org/bouncycastle/math/ec/ECCurve.java
index bf1decfbff..ce879c4159 100644
--- a/core/src/main/java/org/bouncycastle/math/ec/ECCurve.java
+++ b/core/src/main/java/org/bouncycastle/math/ec/ECCurve.java
@@ -845,6 +845,11 @@ public static BigInteger inverse(int m, int[] ks, BigInteger x)
 
         private static FiniteField buildField(int m, int k1, int k2, int k3)
         {
+            if (m > Properties.asInteger("org.bouncycastle.ec.max_f2m_field_size", 1142))  // twice 571
+            {
+                throw new IllegalArgumentException("field size out of range: " + m);
+            }
+
             int[] exponents = (k2 | k3) == 0
                 ? new int[]{ 0, k1, m }
                 : new int[]{ 0, k1, k2, k3, m };
@@ -1006,11 +1011,6 @@ protected ECFieldElement solveQuadraticEquation(ECFieldElement beta)
             }
 
             int m = this.getFieldSize();
-
-            if (m > Properties.asInteger("org.bouncycastle.ec.max_f2m_field_size", 1142))  // twice 571
-            {
-                throw new IllegalStateException("field size out of range: " + m);
-            }
             
             // For odd m, use the half-trace 
             if (0 != (m & 1))
diff --git a/core/src/test/java/org/bouncycastle/math/ec/test/ECPointTest.java b/core/src/test/java/org/bouncycastle/math/ec/test/ECPointTest.java
index f53c98287c..68fd639784 100644
--- a/core/src/test/java/org/bouncycastle/math/ec/test/ECPointTest.java
+++ b/core/src/test/java/org/bouncycastle/math/ec/test/ECPointTest.java
@@ -196,6 +196,25 @@ private void implTestAdd(ECPoint[] p, ECPoint infinity)
         }
     }
 
+    public void testLargeMInF2m()
+    {
+        int m = 2048;
+        int k1 = 1;
+        BigInteger aTpb = new BigInteger("1000", 2);
+        BigInteger bTpb = new BigInteger("1001", 2);
+        BigInteger n = new BigInteger("23");
+        BigInteger h = new BigInteger("1");
+
+        try
+        {
+            ECCurve.F2m curve = new ECCurve.F2m(m, k1, aTpb, bTpb, n, h);
+        }
+        catch (IllegalArgumentException e)
+        {
+            assertEquals("field size out of range: 2048", e.getMessage());
+        }
+    }
+
     /**
      * Calls <code>implTestAdd()</code> for <code>Fp</code> and
      * <code>F2m</code>.