Fixed N4 calculation issue - see BJA-655

1 files changed, 5 insertions, 1 deletions

diff --git a/crypto/src/crypto/modes/GOFBBlockCipher.cs b/crypto/src/crypto/modes/GOFBBlockCipher.cs

index a91562549..4299f11a9 100644
--- a/crypto/src/crypto/modes/GOFBBlockCipher.cs
+++ b/crypto/src/crypto/modes/GOFBBlockCipher.cs
@@ -169,7 +169,11 @@ namespace Org.BouncyCastle.Crypto.Modes
 			}
 			N3 += C2;
 			N4 += C1;
-			intTobytes(N3, ofbV, 0);
+            if (N4 < C1)  // addition is mod (2**32 - 1)
+            {
+                N4++;
+            }
+            intTobytes(N3, ofbV, 0);
 			intTobytes(N4, ofbV, 4);
 
 			cipher.ProcessBlock(ofbV, 0, ofbOutV, 0);