Move XDH/EdDSA key generation into low-level

- Clamp X25519, X448 private keys during generation

2 files changed, 19 insertions, 0 deletions

diff --git a/crypto/src/math/ec/rfc7748/X25519.cs b/crypto/src/math/ec/rfc7748/X25519.cs

index d8db2527a..8524b9e2c 100644
--- a/crypto/src/math/ec/rfc7748/X25519.cs
+++ b/crypto/src/math/ec/rfc7748/X25519.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Diagnostics;
 
+using Org.BouncyCastle.Security;
 using Org.BouncyCastle.Utilities;
 
 namespace Org.BouncyCastle.Math.EC.Rfc7748
@@ -50,6 +51,15 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
             n[7] |= 0x40000000U;
         }
 
+        public static void GeneratePrivateKey(SecureRandom random, byte[] k)
+        {
+            random.NextBytes(k);
+
+            k[0] &= 0xF8;
+            k[ScalarSize - 1] &= 0x7F;
+            k[ScalarSize - 1] |= 0x40;
+        }
+
         private static void PointDouble(int[] x, int[] z)
         {
             int[] A = X25519Field.Create();
diff --git a/crypto/src/math/ec/rfc7748/X448.cs b/crypto/src/math/ec/rfc7748/X448.cs

index 63d34d1cf..63e526703 100644
--- a/crypto/src/math/ec/rfc7748/X448.cs
+++ b/crypto/src/math/ec/rfc7748/X448.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Diagnostics;
 
+using Org.BouncyCastle.Security;
 using Org.BouncyCastle.Utilities;
 
 namespace Org.BouncyCastle.Math.EC.Rfc7748
@@ -52,6 +53,14 @@ namespace Org.BouncyCastle.Math.EC.Rfc7748
             n[13] |= 0x80000000U;
         }
 
+        public static void GeneratePrivateKey(SecureRandom random, byte[] k)
+        {
+            random.NextBytes(k);
+
+            k[0] &= 0xFC;
+            k[ScalarSize - 1] |= 0x80;
+        }
+
         private static void PointDouble(uint[] x, uint[] z)
         {
             uint[] A = X448Field.Create();