begin adding support for in-document security handlers to support aes 128/256 encryption #34

src/UglyToad.PdfPig/Encryption/CryptHandler.cs

@@ -0,0 +1,101 @@
+namespace UglyToad.PdfPig.Encryption
+{
+    using System;
+    using Exceptions;
+    using Tokens;
+
+    internal class CryptHandler
+    {
+        private readonly DictionaryToken cryptDictionary;
+
+        public CryptDictionary StreamDictionary { get; }
+
+        public CryptDictionary StringDictionary { get; }
+
+        public CryptHandler(DictionaryToken cryptDictionary,
+            NameToken streamName, NameToken stringName)
+        {
+            if (streamName == null)
+            {
+                throw new ArgumentNullException(nameof(streamName));
+            }
+
+            if (stringName == null)
+            {
+                throw new ArgumentNullException(nameof(stringName));
+            }
+
+            this.cryptDictionary = cryptDictionary ?? throw new ArgumentNullException(nameof(cryptDictionary));            
+            StreamDictionary = ParseCryptDictionary(cryptDictionary, streamName);
+            StringDictionary = ParseCryptDictionary(cryptDictionary, stringName);
+        }
+
+        public CryptDictionary GetNamedCryptDictionary(NameToken name)
+        {
+            if (name == null)
+            {
+                throw new ArgumentNullException(nameof(name));
+            }
+
+            return ParseCryptDictionary(cryptDictionary, name);
+        }
+
+        private static CryptDictionary ParseCryptDictionary(DictionaryToken cryptDictionary, NameToken name)
+        {
+            if (name == NameToken.Identity)
+            {
+                return CryptDictionary.Identity;
+            }
+
+            if (!cryptDictionary.TryGet(name, out DictionaryToken cryptDictionaryToken))
+            {
+                throw new PdfDocumentEncryptedException($"Could not find named crypt filter {name} for decryption in crypt dictionary: {cryptDictionaryToken}.");
+            }
+
+            if (cryptDictionaryToken.TryGet(NameToken.Type, out NameToken typeName) && typeName != NameToken.CryptFilter)
+            {
+                throw new PdfDocumentEncryptedException($"Invalid crypt dictionary type {typeName} for crypt filter {name}: {cryptDictionaryToken}.");
+            }
+
+            var cfmName = cryptDictionaryToken.TryGet(NameToken.Cfm, out NameToken cfm) ? cfm : NameToken.None;
+
+            CryptDictionary.Method method;
+            if (cfmName == NameToken.None)
+            {
+                method = CryptDictionary.Method.None;
+            }
+            else if (cfmName == NameToken.V2)
+            {
+                method = CryptDictionary.Method.V2;
+            }
+            else if (cfmName == NameToken.Aesv2)
+            {
+                method = CryptDictionary.Method.AesV2;
+            }
+            else
+            {
+                throw new PdfDocumentEncryptedException($"Unrecognized CFM option for crypt filter {cfm}: {cryptDictionaryToken}.");
+            }
+
+            var eventName = cryptDictionaryToken.TryGet(NameToken.AuthEvent, out NameToken auth) ? auth : NameToken.DocOpen;
+
+            CryptDictionary.TriggerEvent @event;
+            if (eventName == NameToken.DocOpen)
+            {
+                @event = CryptDictionary.TriggerEvent.DocumentOpen;
+            }
+            else if (eventName == NameToken.EfOpen)
+            {
+                @event = CryptDictionary.TriggerEvent.EmbeddedFileOpen;
+            }
+            else
+            {
+                throw new PdfDocumentEncryptedException($"Unrecognized AuthEvent option for crypt filter {eventName}: {cryptDictionaryToken}.");
+            }
+
+            var length = cryptDictionaryToken.TryGet(NameToken.Length, out NumericToken lengthNumeric) ? lengthNumeric.Int : 0;
+
+            return new CryptDictionary(method, @event, length);
+        }
+    }
+}