Merge pull request #212 from WitkacDevelopers/fix/sigfields_with_multiple_instances

Fix handling of signature fields with multiple instances

Author: VahidN

src/iTextSharp.LGPLv2.Core.FunctionalTests/PdfVerifySignatureTests.cs

@@ -0,0 +1,45 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using iTextSharp.text;
+using iTextSharp.text.pdf;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace iTextSharp.LGPLv2.Core.FunctionalTests;
+
+[TestClass]
+public class PdfVerifySignatureTests
+{
+    [TestMethod]
+    public void Detect_Singature_Fields()
+    {
+        var filename = Path.Combine(TestUtils.GetBaseDir(), "iTextExamples", "resources", "pdfs", "issue_sig_fields.pdf");
+        using var reader = new PdfReader(filename);
+        var fields = reader.AcroFields;
+        var names = fields.GetSignatureNames();
+        Assert.AreEqual(1, names.Count);
+        
+
+    }
+    
+    [TestMethod]
+    public void Detect_PKCS7()
+    {
+        var filename = Path.Combine(TestUtils.GetBaseDir(), "iTextExamples", "resources", "pdfs", "issue_sig_fields.pdf");
+        using var reader = new PdfReader(filename);
+        var fields = reader.AcroFields;
+        var names = fields.GetSignatureNames();
+        Assert.AreEqual(1, names.Count);
+
+        var cover = fields.SignatureCoversWholeDocument(names[0]);
+        Assert.IsTrue(cover);
+        
+        
+        
+        var pkcs7 = fields.VerifySignature(names[0]);
+        Assert.IsNotNull(pkcs7);
+        Assert.IsTrue(pkcs7.Verify());
+    }
+
+
+}

src/iTextSharp.LGPLv2.Core.FunctionalTests/iTextExamples/resources/pdfs/issue_sig_fields.pdf

@@ -1298,6 +1298,8 @@ public int GetRevision(string field)
 
         return value[1];
     }
+    
+
 
     /// <summary>
     ///     Gets the signature dictionary, the one keyed by /V.
@@ -1316,9 +1318,14 @@ public PdfDictionary GetSignatureDictionary(string name)
         }
 
         var item = fields[name];
-        var merged = item.GetMerged(idx: 0);
+        
+        //get first merged  dicionary with /V key
+        var merged = item.Merged.FirstOrDefault(x=>x.Contains(PdfName.V));
 
+        if (merged == null) return null;
         return merged.GetAsDict(PdfName.V);
+
+
     }
 
     /// <summary>
@@ -2966,8 +2973,15 @@ private void findSignatureNames()
         foreach (var entry in fields)
         {
             var item = entry.Value;
-            var merged = item.GetMerged(idx: 0);
-
+            
+            // find first merged dictionary with /V
+            var merged = item.Merged.FirstOrDefault(x => x.Contains(PdfName.V));
+            
+            if (merged== null)
+            {
+                continue;
+            }
+          
             if (!PdfName.Sig.Equals(merged.Get(PdfName.Ft)))
             {
                 continue;
@@ -3242,6 +3256,7 @@ public class Item
         /// <param name="idx">instance index</param>
         /// <returns>the merged dictionary for the given instance</returns>
         public PdfDictionary GetMerged(int idx) => Merged[idx];
+        
 
         /// <summary>
         ///     Retrieve the page number of the given instance