add support for aes-128 decryption #34

src/UglyToad.PdfPig.Tests/Encryption/AesEncryptionHelperTests.cs

@@ -0,0 +1,29 @@
+using Xunit;
+
+namespace UglyToad.PdfPig.Tests.Encryption
+{
+    using PdfPig.Encryption;
+    using PdfPig.Util;
+
+    public class AesEncryptionHelperTests
+    {
+        [Fact]
+        public void CanDecryptDateString()
+        {
+            var key = new byte[]
+            {
+                54, 109, 249, 186, 109, 210, 209, 44, 94, 28, 227, 232, 73, 86, 128, 186
+            };
+
+            var data = new byte[]
+            {
+                123, 28, 227, 85, 79, 126, 149, 28, 211, 96, 199, 192, 105, 149, 76, 231,
+                8, 136, 51, 141, 139, 44, 0, 230, 228, 116, 12, 145, 132, 157, 5, 123, 235, 247, 232, 244, 36, 217, 73, 147, 157, 124, 27, 143, 255, 79, 220, 194
+            };
+
+            var output = AesEncryptionHelper.Decrypt(data, key);
+
+            Assert.Equal("D:20180808103317-07'00'", OtherEncodings.BytesAsLatin1String(output));
+        }
+    }
+}

src/UglyToad.PdfPig/Content/Pages.cs

@@ -2,7 +2,6 @@
 {
     using System;
     using System.Collections.Generic;
-    using Geometry;
     using Logging;
     using Parser.Parts;
     using Tokenization.Scanner;

src/UglyToad.PdfPig/Encryption/AesEncryptionHelper.cs

@@ -0,0 +1,50 @@
+namespace UglyToad.PdfPig.Encryption
+{
+    using System;
+    using System.IO;
+    using System.Security.Cryptography;
+
+    internal static class AesEncryptionHelper
+    {
+        public static byte[] Encrypt256()
+        {
+            throw new NotImplementedException();
+        }
+
+        public static byte[] Decrypt(byte[] data, byte[] finalKey)
+        {
+            var iv = new byte[16];
+            Array.Copy(data, iv, iv.Length);
+            
+            using (var rijndael = Rijndael.Create())
+            {
+                rijndael.Key = finalKey;
+                rijndael.IV = iv;
+
+                var buffer = new byte[256];
+
+                using (var decryptor = rijndael.CreateDecryptor(rijndael.Key, rijndael.IV))
+                using (var input = new MemoryStream(data))
+                using (var output = new MemoryStream())
+                {
+                    input.Seek(iv.Length, SeekOrigin.Begin);
+                    using (var cryptoStream = new CryptoStream(input, decryptor, CryptoStreamMode.Read))
+                    {
+                        int read;
+                        while ((read = cryptoStream.Read(buffer, 0, buffer.Length)) != -1)
+                        {
+                            output.Write(buffer, 0, read);
+
+                            if (read < buffer.Length)
+                            {
+                                break;
+                            }
+                        }
+
+                        return output.ToArray();
+                    }
+                }
+            }
+        }
+    }
+}

src/UglyToad.PdfPig/Encryption/EncryptionHandler.cs

@@ -358,7 +358,7 @@
 
             if (useAes)
             {
-                throw new PdfDocumentEncryptedException("Decryption for AES-128 not currently supported.", encryptionDictionary);
+                return AesEncryptionHelper.Decrypt(data, finalKey);
             }
 
             return RC4.Encrypt(finalKey, data);