/* This class has been written by
* Corinna John (Hannover, Germany)
* cj@binary-universe.net
*
* You may do with this code whatever you like,
* except selling it or claiming any rights/ownership.
*
* Please send me a little feedback about what you're
* using this code for and what changes you'd like to
* see in later versions. (And please excuse my bad english.)
*
* WARNING: This is experimental code.
* Exception handling has been omitted,
* to keep the code readable to people who want
* to understand the algorithm.
* Please do not expect "Release Quality".
* */
#region Using directives
using System;
using System.IO;
using System.Data;
using System.Text;
using System.Collections;
using System.Collections.Specialized;
#endregion
namespace SteganoHtml {
public class HtmlUtility {
public HtmlUtility() {}
/// <summary>Counts the key attribute couples in an HTML document</summary>
/// <param name="sourceFileName">Path and name of the HTML document</param>
/// <param name="keyTable">DataTable with the key attributes</param>
/// <returns>Count of bytes that can be hidden in the specified document</returns>
public int GetCapacity(String sourceFileName, DataTable keyTable) {
int countCarrierCouples = 0;
StreamReader reader = new StreamReader(sourceFileName, Encoding.Default);
String htmlDocument = reader.ReadToEnd();
reader.Close();
HtmlTagCollection tags = FindTags(htmlDocument);
StringBuilder insertTextBuilder = new StringBuilder();
DataRow[] rows;
HtmlAttribute secondAttribute;
foreach (HtmlTag tag in tags) {
foreach (HtmlAttribute attribute in tag.Attributes) {
if (!attribute.Handled) {
rows = keyTable.Select("firstAttribute = '" + attribute.Name.Replace("'", "''") + "'");
if (rows.Length > 0) {
secondAttribute = FindAttribute(rows[0]["secondAttribute"].ToString(), tag.Attributes);
if (secondAttribute != null) {
countCarrierCouples++;
}
}
}
}
}
return countCarrierCouples;
}
/// <summary>Encode one bit as a combination of attributes, add the resulting text to a StringBuilder</summary>
/// <param name="messageByte">Current byte</param>
/// <param name="bitIndex">Current position in [messageByte]</param>
/// <param name="firstAttribute">Key attribute</param>
/// <param name="secondAttribute">Corresponding attribute</param>
/// <param name="insertTextBuilder">Receives the new HTML text</param>
private void HideBit(int messageByte, int bitIndex, HtmlAttribute firstAttribute, HtmlAttribute secondAttribute, StringBuilder insertTextBuilder) {
String firstAttributeText, secondAttributeText;
if (firstAttribute.Value.Length > 0) {
firstAttributeText = String.Format("{0}={1}", firstAttribute.Name, firstAttribute.Value);
} else {
firstAttributeText = firstAttribute.Name;
}
if (secondAttribute.Value.Length > 0) {
secondAttributeText = String.Format("{0}={1}", secondAttribute.Name, secondAttribute.Value);
} else {
secondAttributeText = secondAttribute.Name;
}
if (GetBit(messageByte, bitIndex)) {
//bit is true
insertTextBuilder.AppendFormat(
@" {0} {1}",
firstAttributeText,
secondAttributeText);
} else {
//bit is false
insertTextBuilder.AppendFormat(
@" {0} {1}",
secondAttributeText,
firstAttributeText);
}
}
/// <summary>Hide a message in an HTML document</summary>
/// <param name="sourceFileName">Path and name of the HTML document</param>
/// <param name="destinationFileName">Path and name to save the resulting HTML document</param>
/// <param name="message">The message to hide</param>
/// <param name="keyTable">DataTable with the key attributes</param>
public void Hide(String sourceFileName, String destinationFileName, Stream message, DataTable keyTable) {
//read the carrier document
StreamReader reader = new StreamReader(sourceFileName, Encoding.Default);
String htmlDocument = reader.ReadToEnd();
reader.Close();
message.Position = 0;
//list the HTML tags
HtmlTagCollection tags = FindTags(htmlDocument);
StringBuilder insertTextBuilder = new StringBuilder();
DataRow[] rows;
HtmlAttribute secondAttribute;
int offset = 0;
int bitIndex = 7;
int messageByte = 0;
foreach (HtmlTag tag in tags) {
insertTextBuilder.Remove(0, insertTextBuilder.Length);
insertTextBuilder.AppendFormat("<{0}", tag.Name);
foreach (HtmlAttribute attribute in tag.Attributes) {
if (!attribute.Handled) { //attribute has not been used, yet
//find key row for this attribute
rows = keyTable.Select(String.Format("firstAttribute = '{0}'", attribute.QueryFormattedName));
if (rows.Length > 0) {
//find corresponding attribute
secondAttribute = FindAttribute(rows[0]["secondAttribute"].ToString(), tag.Attributes);
if (secondAttribute != null) {
if (bitIndex == 7) {
//get next message byte
bitIndex = 0;
messageByte = message.ReadByte();
} else {
//next bit
bitIndex++;
}
//change the attributes' order
HideBit(messageByte, bitIndex, attribute, secondAttribute, insertTextBuilder);
//mark both attributes as handled
attribute.Handled = true;
secondAttribute.Handled = true;
}
}
if (!attribute.Handled) {
//the attribute is not a primary key attribute. Is it a secondary key attribute?
bool copyAttribute = false;
rows = keyTable.Select(String.Format("secondAttribute = '{0}'", attribute.QueryFormattedName));
if(rows.Length > 0){
//if the corresponding first attribute does not exist in this tag or has already been used,
//this attribute will not be used and must be copied.
HtmlAttribute firstAttribute = FindAttribute(rows[0]["firstAttribute"].ToString(), tag.Attributes);
if (firstAttribute == null) {
copyAttribute = true;
}else{
copyAttribute = firstAttribute.Handled;
}
}
else if (rows.Length == 0) {
//this attribute is not part of the key and must be copied.
copyAttribute = true;
}
if (copyAttribute) {
//copy unused attribute
insertTextBuilder.AppendFormat(
@" {0}={1}",
attribute.Name, attribute.Value);
attribute.Handled = true;
}
}
}
}
//replace old tag with new tag
tag.BeginPosition += offset;
tag.EndPosition += offset;
String insertText = insertTextBuilder.ToString();
int newLength = insertText.Length;
if (newLength > 0) {
int oldLength = tag.EndPosition - tag.BeginPosition;
htmlDocument = htmlDocument.Remove(tag.BeginPosition, oldLength);
htmlDocument = htmlDocument.Insert(tag.BeginPosition, insertText);
offset += (newLength - oldLength);
}
if (messageByte < 0) {
break; //finished
}
}
//save the new document
StreamWriter writer = new StreamWriter(destinationFileName);
writer.Write(htmlDocument);
writer.Close();
}
/// <summary>Extract one bit, add it to a Stream</summary>
/// <param name="firstAttributePosition">Position of the key attribute in the source document</param>
/// <param name="secondAttributePosition">Position of the corresponding attribute in the source document</param>
/// <param name="messageByte">Current message byte</param>
/// <param name="bitIndex">Current bit index</param>
/// <param name="message">Message stream</param>
/// <returns>New message byte</returns>
private byte ExtractBit(int firstAttributePosition, int secondAttributePosition, byte messageByte, int bitIndex, Stream message) {
if (firstAttributePosition < secondAttributePosition) {
messageByte = SetBit(messageByte, bitIndex, true);
} else {
messageByte = SetBit(messageByte, bitIndex, false);
}
if (bitIndex == 7) {
//save to message byte
message.WriteByte(messageByte);
messageByte = 0;
}
return messageByte;
}
/// <summary>Extract a hidden message from an HTML document</summary>
/// <param name="sourceFileName">Path and name of the HTML document</param>
/// <param name="message">Empty stream for the message</param>
/// <param name="keyTable">DataTable with the key attributes</param>
public void Extract(String sourceFileName, Stream message, DataTable keyTable) {
//read the carrier document
StreamReader reader = new StreamReader(sourceFileName, Encoding.Default);
String htmlDocument = reader.ReadToEnd();
reader.Close();
//list the HTML tags
HtmlTagCollection tags = FindTags(htmlDocument);
StringBuilder insertTextBuilder = new StringBuilder();
DataRow[] rows;
HtmlAttribute secondAttribute;
int attributePosition, secondAttributePosition;
int messageLength = 0;
int bitIndex = 0;
byte messageByte = 0;
foreach (HtmlTag tag in tags) {
foreach (HtmlAttribute attribute in tag.Attributes) {
if (!attribute.Handled) { //attribute has not been used, yet
//find key row for this attribute
rows = keyTable.Select(String.Format("firstAttribute = '{0}'", attribute.QueryFormattedName));
if (rows.Length > 0) {
//find corresponding attribute
secondAttribute = FindAttribute(rows[0]["secondAttribute"].ToString(), tag.Attributes);
if (secondAttribute != null) {
attributePosition = htmlDocument.IndexOf(attribute.Name, tag.BeginPosition);
secondAttributePosition = htmlDocument.IndexOf(secondAttribute.Name, tag.BeginPosition);
//compare the attributes' positions
messageByte = ExtractBit(attributePosition, secondAttributePosition, messageByte, bitIndex, message);
//next bit
if (bitIndex == 7) {
bitIndex = 0;
if ((message.Length == 1) && (messageLength == 0)) {
//read length
message.Position = 0;
BinaryReader binaryReader = new BinaryReader(message);
messageLength = binaryReader.ReadByte();
reader = null;
message.SetLength(0);
message.Position = 0;
}
else if ((messageLength > 0) && (message.Length == messageLength)) {
break; //finished
}
} else {
bitIndex++;
}
//mark both attributes as handled
attribute.Handled = true;
secondAttribute.Handled = true;
}
}
if (!attribute.Handled) {
rows = keyTable.Select(String.Format("secondAttribute = '{0}'", attribute.QueryFormattedName));
if (rows.Length == 0) {
//tag not used
attribute.Handled = true;
}
}
}
}
if ((messageLength > 0) && (message.Length == messageLength)) {
break; //finished
}
}
}
/// <summary>Find the attribute with a specific name</summary>
/// <param name="name">Name of the attribute</param>
/// <param name="attributes">Attributes of a tag</param>
/// <returns>The attribute found in [attributes], or null</returns>
private HtmlAttribute FindAttribute(String name, HtmlAttributeCollection attributes) {
HtmlAttribute foundAttribute = null;
foreach (HtmlAttribute attribute in attributes) {
if ((!attribute.Handled) && (attribute.Name == name)) {
foundAttribute = attribute;
break;
}
}
return foundAttribute;
}
/// <summary>List all HTML tags of a document</summary>
/// <param name="htmlDocument"></param>
/// <returns>List with</returns>
private HtmlTagCollection FindTags(String htmlDocument) {
HtmlTagCollection tags = new HtmlTagCollection();
int indexStart = 0, indexEnd = 0;
String text;
do {
indexStart = htmlDocument.IndexOf('<', indexEnd + 1);
if (indexStart > 0) {
indexEnd = htmlDocument.IndexOf('>', indexStart + 1);
if (indexEnd > 0) {
if (htmlDocument[indexStart + 1] != '/') {
//Ende vom Start-Tag gefunden
text = htmlDocument.Substring(indexStart, indexEnd - indexStart);
tags.Add(new HtmlTag(text, indexStart, indexEnd));
}
}
}
} while (indexStart > 0);
return tags;
}
/// <summary>Get the value of a bit</summary>
/// <param name="b">The byte value</param>
/// <param name="position">The position of the bit</param>
/// <returns>The value of the bit</returns>
private bool GetBit(int b, int position) {
return ((b & (byte)(1 << position)) != 0);
}
/// <summary>Set a bit to [newBitValue]</summary>
/// <param name="b">The byte value</param>
/// <param name="position">The position (1-8) of the bit</param>
/// <param name="newBitValue">The new value of the bit in position [position]</param>
/// <returns>The new byte value</returns>
private byte SetBit(byte b, int position, bool newBitValue) {
byte mask = (byte)(1 << position);
if (newBitValue) {
return (byte)(b | mask);
} else {
return (byte)(b & ~mask);
}
}
}
}
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