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Posted 18 Feb 2004

# Tiny Encryption Algorithm (TEA) for the Compact Framework

, 29 Feb 2004
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Learn how to secure sensitive data using TEA encryption.

## Introduction

The Compact Framework omits the main encryption features in the Cryptography namespace to make room for more important features. Fortunately, it is not terribly difficult to implement some sort of cryptography to hide your sensitive data. I wanted to find a small algorithm that was secure and portable. After doing a little searching, I ran across the Tiny Encryption Algorithm (TEA). This algorithm was developed in 1994 by David Wheeler and Roger Needham of Cambridge University. This algorithm is extremely portable, and fast. There has been a successful cryptanalysis performed on the original TEA algorithm which caused the original authors to modify the TEA algorithm. The revised algorithm is called XTEA. There is not much information on this algorithm so there is no guarantee that the XTEA algorithm has not been broken as well. However, this algorithm could still be useful for applications that do not require the highest of security. The original algorithm was developed in C, but constructed in such a way that it is easy to port to other languages, like C#. I was able to port the original C algorithm to C# with minimal changes. I tested the algorithm on the full .NET Framework as well as the .NET Compact Framework and it works great on both platforms with no changes.
For more information on how TEA encryption works, refer to the links at the bottom of this article.

## Background

The Tiny Encryption Algorithm works on the principle of paired blocks of data. This makes it a little more challenging to prepare strings for encryption because you need to pass pairs of unsigned integers to the algorithm and then store them in some manner so the data can be recovered at a later point in time. I use some bit shifting to convert between integers and strings, so a little knowledge of number systems will help you out.

## Using the code

Porting the code to C# was the easy part. After porting the C algorithm to C#, I ended up with the following function for encryption:

private void code(uint[] v, uint[] k)
{
uint y = v[0];
uint z = v[1];
uint sum = 0;
uint delta=0x9e3779b9;
uint n=32;

while(n-->0)
{
y += (z << 4 ^ z >> 5) + z ^ sum + k[sum & 3];
sum += delta;
z += (y << 4 ^ y >> 5) + y ^ sum + k[sum >> 11 & 3];
}

v[0]=y;
v[1]=z;
}

Simple huh? They don't call it tiny for nothing! Here is the decrypt function:

private void decode(uint[] v, uint[] k)
{
uint n=32;
uint sum;
uint y=v[0];
uint z=v[1];
uint delta=0x9e3779b9;

sum = delta << 5 ;

while(n-->0)
{
z -= (y << 4 ^ y >> 5) + y ^ sum + k[sum >> 11 & 3];
sum -= delta;
y -= (z << 4 ^ z >> 5) + z ^ sum + k[sum & 3];
}

v[0]=y;
v[1]=z;
}

Note: I only modified what was necessary to get the code to compile. I also formatted the code to make it a little more readable. In the original algorithm, they used an unsigned long for the variables. In C, an unsigned is a 32-bit unsigned integer. In .NET land, the equivalent is an unsigned integer.

Now we have reached the challenging part. To use the algorithm with strings, we have to convert the strings into an acceptable format. Here is a basic run-through of what I did to make use of the algorithm:

• Make the string an even length by adding a space to the end of it if necessary. We need to do this because the algorithm expects pairs of data.
• Convert the string to an array of bytes.
• Loop through the array and pass a pair of values to the encrypt function.
• Convert the two cipher values to strings and append to one long string.

My Encrypt function looks something like the following:

public string Encrypt(string Data, string Key)
{
uint[] formattedKey = FormatKey(Key);

if(Data.Length%2!=0) Data += '\0'; // Make sure array is even in length.
byte[] dataBytes = System.Text.ASCIIEncoding.ASCII.GetBytes(Data);

string cipher = string.Empty;
uint[] tempData = new uint[2];
for(int i=0; i<dataBytes.Length; i+=2)
{
tempData[0] = dataBytes[i];
tempData[1] = dataBytes[i+1];
code(tempData, formattedKey);
cipher += ConvertUIntToString(tempData[0]) +
ConvertUIntToString(tempData[1]);
}

return cipher;
}

The Decrypt function basically is just the reverse of the encrypt function:

public string Decrypt(string Data, string Key)
{
uint[] formattedKey = FormatKey(Key);

int x = 0;
uint[] tempData = new uint[2];
byte[] dataBytes = new byte[Data.Length / 8 * 2];
for(int i=0; i<Data.Length; i+=8)
{
tempData[0] = ConvertStringToUInt(Data.Substring(i, 4));
tempData[1] = ConvertStringToUInt(Data.Substring(i+4, 4));
decode(tempData, formattedKey);
dataBytes[x++] = (byte)tempData[0];
dataBytes[x++] = (byte)tempData[1];
}

string decipheredString =
System.Text.ASCIIEncoding.ASCII.GetString(dataBytes,
0, dataBytes.Length);

// Strip the null char if it was added.
if(decipheredString[decipheredString.Length - 1] == '\0')
decipheredString = decipheredString.Substring(0,
decipheredString.Length - 1);
return decipheredString;
}
The ConvertUIntToString function takes advantage of some shifting and bitwise-anding (&) to convert a 32-bit unsigned integer to a string of length 4. Since a character is 1 byte in length, we can combine 4 characters to make 4 bytes or 32 bits. Gee, that would hold a 32-bit unsigned integer (uint) nicely! Wow!
private string ConvertUIntToString(uint Input)
{
System.Text.StringBuilder output = new System.Text.StringBuilder();
output.Append((char)((Input & 0xFF)));
output.Append((char)((Input >> 8) & 0xFF));
output.Append((char)((Input >> 16) & 0xFF));
output.Append((char)((Input >> 24) & 0xFF));
return output.ToString();
}

Here is the function to undo what ConvertUIntToString does:

private uint ConvertStringToUInt(string Input)
{
uint output;
output =  ((uint)Input[0]);
output += ((uint)Input[1] << 8);
output += ((uint)Input[2] << 16);
output += ((uint)Input[3] << 24);
return output;
}

Anding the shifted Input with 0xFF will cause only 1 byte to be returned.
The sample code includes a sample application for the .NET Framework and the .NET Compact Framework.

## Points of Interest

• The original Tiny Encryption Algorithm can be found here.
• Another site with some information on this algorithm can be found here.
• In depth article on TEA framework

## History

• 29 Feb 2004 - Added XTEA Algorithm to the article and source code.
• 19 Feb 2004 - Original Article.

## License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

## About the Author

 Software Developer (Senior) United States
Check out my blog! http://www.pagebrooks.com

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## Comments and Discussions

 First PrevNext
 Not TEA algorithm Lord Veovis28-May-17 5:02 Lord Veovis 28-May-17 5:02
 Doesn't work at all masiton21-Sep-14 6:40 masiton 21-Sep-14 6:40
 My vote of 5 BlckHwk19-Jun-13 13:13 BlckHwk 19-Jun-13 13:13
 Arbitrary decode utility Bug Me Not23-Nov-09 7:36 Bug Me Not 23-Nov-09 7:36
 FormatKey ciu221-Oct-09 4:45 ciu2 21-Oct-09 4:45
 ÄÜÖ == ? MixxerY6-Feb-09 4:21 MixxerY 6-Feb-09 4:21
 Re: ÄÜÖ == ? Member 603819614-Aug-09 0:25 Member 6038196 14-Aug-09 0:25
 very importatnt::: tea encryption with sql server rashad61212-Dec-07 1:59 rashad612 12-Dec-07 1:59
 hi all,, i have this problem.. i use the tea encryption with MS SQL DB. i store the encrypted msg in a field of a table, then store the key in another field.. But when i retreive the encrypted msg with its key.. and try to (decrypt) it.. it changes into another encrypted string.. this probleb happens only with strings retreived from SQL DB. what should i do????!!!!!!!!! Rashad.S.Majali
 very importatnt::: tea encryption with sql server rashad61212-Dec-07 1:58 rashad612 12-Dec-07 1:58
 save to XML? tonypigram17-Nov-06 8:08 tonypigram 17-Nov-06 8:08
 Re: save to XML? sandhyas30-Jul-09 1:59 sandhyas 30-Jul-09 1:59
 Major Flaw in the algorythm [modified] jkcode24-Jul-06 9:48 jkcode 24-Jul-06 9:48
 Re: Major Flaw in the algorythm rhinodude3-Dec-06 5:30 rhinodude 3-Dec-06 5:30
 Re: Major Flaw in the algorythm jkcode4-Dec-06 8:38 jkcode 4-Dec-06 8:38
 Re: Major Flaw in the algorythm [modified] Tom Calloway3-Feb-09 4:29 Tom Calloway 3-Feb-09 4:29
 C++ TEA Implementation? nemrac986-Jul-06 5:18 nemrac98 6-Jul-06 5:18
 Endianness D. Emilio Grimaldo Tuñon6-Jul-06 5:08 D. Emilio Grimaldo Tuñon 6-Jul-06 5:08
 A suggestion D. Emilio Grimaldo Tuñon6-Jul-06 3:32 D. Emilio Grimaldo Tuñon 6-Jul-06 3:32
 problem Cyber2217-Apr-06 6:31 Cyber22 17-Apr-06 6:31
 Re: problem Jens S4-Feb-08 7:52 Jens S 4-Feb-08 7:52
 Re: problem Jens S4-Feb-08 9:50 Jens S 4-Feb-08 9:50
 VB.NET Implementation santakdas24-Oct-05 13:37 santakdas 24-Oct-05 13:37
 Re: VB.NET Implementation [modified] meibella17-Jul-07 18:35 meibella 17-Jul-07 18:35
 Re: VB.NET Implementation MatthiasBroschk19-Nov-09 9:21 MatthiasBroschk 19-Nov-09 9:21
 VB.NET Implementation santakdas24-Oct-05 13:35 santakdas 24-Oct-05 13:35
 Last Visit: 31-Dec-99 19:00     Last Update: 24-Jan-18 0:17 Refresh 123 Next »

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