System.Security.Cryptography.CryptographicException: Length of the data to decrypt is invalid

I am new to encryption and have run into an issue with a small encryption/decryption class I created (which is a blend of a few different pieces I came across on the internet). I have found that while most strings work with the four symmetric algorithms I have enabled for the class (DES, RC2, Rijndael, and TripleDES), sometimes I receive a cryptographicexception Length of the data to decrypt is invalid. My impression is that it has something to do with the block sizes required by each algorithm, but am unclear why it allows me to encrypt a string using a particular algorithm, but then fails on the decryption. To that end, I have no idea as to what needs to be done to fix it so that I get 100% encryption/decryption based on a string and supplied key. I have built a small webform to test the class, which allows me to enter the string, key, and select the desired algorithm. Anything that can be explained to shed light on this issue would be greatly appreciated. Thanks in advance. Code is below (class, html for webform, codebehind for webform) class CryptoSymmetric /******************************************************************/ using System; using System.IO; using System.Text; using System.Security.Cryptography; namespace CSCodeSamples { ///

/// Summary description for SymmCrypto2. ///

public class CryptoSymmetric { public enum EncryptionAlgorithm { DES, RC2, Rijndael, TripleDES } private enum CryptoMethod { Encrypt, Decrypt } private SymmetricAlgorithm objCryptoService; private EncryptionAlgorithm algorithmID; private byte[] bytesKey; private byte[] bytesIV; public byte[] EncryptionKey { get { return bytesKey; } set { bytesKey = value; } } public byte[] EncryptionIV { get { return bytesIV; } set { bytesIV = value; } } /// /// Constructor for using an intrinsic .Net SymmetricAlgorithm class. /// public CryptoSymmetric(EncryptionAlgorithm CryptoSelected) { switch (CryptoSelected) { case EncryptionAlgorithm.DES: { objCryptoService = new DESCryptoServiceProvider(); algorithmID = EncryptionAlgorithm.DES; break; } case EncryptionAlgorithm.RC2: { objCryptoService = new RC2CryptoServiceProvider(); algorithmID = EncryptionAlgorithm.RC2; break; } case EncryptionAlgorithm.Rijndael: { objCryptoService = new RijndaelManaged(); algorithmID = EncryptionAlgorithm.Rijndael; break; } case EncryptionAlgorithm.TripleDES: { objCryptoService = new TripleDESCryptoServiceProvider(); algorithmID = EncryptionAlgorithm.TripleDES; break; } } } private ICryptoTransform CreateServiceProvider(byte[] bKey, CryptoMethod method) { // Pick the provider. switch (algorithmID) { case EncryptionAlgorithm.DES: { objCryptoService = new DESCryptoServiceProvider(); objCryptoService.Mode = CipherMode.CBC; break; } case EncryptionAlgorithm.TripleDES: { objCryptoService = new TripleDESCryptoServiceProvider(); objCryptoService.Mode = CipherMode.CBC; break; } case EncryptionAlgorithm.RC2: { objCryptoService = new RC2CryptoServiceProvider(); objCryptoService.Mode = CipherMode.CBC; break; } case EncryptionAlgorithm.Rijndael: { objCryptoService = new RijndaelManaged(); objCryptoService.Mode = CipherMode.CBC; break; } default: { throw new CryptographicException("Algorithm ID '" + algorithmID + "' not supported."); } } // set up the KEY and IV bytesKey = bKey; if (bytesIV == null) { bytesIV = bKey; } // now determine whether to send back the encryptor or decryptor switch(method) { case CryptoMethod.Encrypt: return objCryptoService.CreateEncryptor(bytesKey, bytesIV); case CryptoMethod.Decrypt: return objCryptoService.CreateDecryptor(bytesKey, bytesIV); default: { throw new CryptographicException("Method '" + method + "' not supported."); } } } private byte[] GetLegalKey(string Key) { string sTemp; if (objCryptoService.LegalKeySizes.Length > 0) { int lessSize = 0, moreSize = objCryptoService.LegalKeySizes[0].MinSize; // key sizes are in bits while (Key.Length * 8 > moreSize) { lessSize = moreSize; moreSize += objCryptoService.LegalKeySizes[0].SkipSize; } sTemp = Key.PadRight(moreSize / 8, ' '); } else sTemp = Key; // convert the secret key to byte array return ASCIIEncoding.ASCII.GetBytes(sTemp); } public string Encrypt(string Source, string Key) { byte[] bInput = System.Text.ASCIIEncoding.ASCII.GetBytes(Source); // create a MemoryStream so that the process can be done without I/O files System.IO.MemoryStream ms = new System.IO.MemoryStream(); byte[] bKey = GetLegalKey(Key); // create an Encryptor ICryptoTransform encrypto = CreateServiceProvider(bKey, CryptoMethod.Encrypt); // create Crypto Stream that transforms a stream using the encryption CryptoStream cs = new CryptoStream(ms, encrypto, CryptoStreamMode.Write); // write out encrypted content into MemoryStream cs.Write(bInput, 0, bInput.Length); cs.FlushFinalBlock(); // get the output and trim the '\0' bytes byte[] bOutput = ms.GetBuffer(); int i = 0; for (i = 0; i < bOutput.Length; i++) if (bOutput[i] == 0) break; // convert into Base64 so that the result can be used in xml return Convert.ToBase64String(bOutput, 0, i); } public string Decrypt(string Source, string Key) { // convert from Base64 to binary byte[] bInput = System.Convert.FromBase64String(Source); // create a MemoryStream with the input System.IO.MemoryStream ms = new System.IO.MemoryStream(bInput, 0, bInput.Length); byte[] bKey = GetLegalKey(Key); // create a Decryptor ICryptoTransform decrypto = CreateServiceProvider(bKey, CryptoMethod.Decrypt); // create Crypto Stream that transforms a stream using the decryption CryptoStream cs = new CryptoStream(ms, decrypto, CryptoStreamMode.Read); // read out the result from the Crypto Stream System.IO.StreamReader sr = new System.IO.StreamReader(cs); return sr.ReadToEnd(); } } } html for webform CryptoForm /******************************************************************/ <%@ Page language="c#" Codebehind="CryptoForm.aspx.cs" AutoEventWireup="false" Inherits="CSCodeSamples.CryptoForm" %> CryptoForm

Reset
Symmetric Encryption

Sample Text :
Sample Key :


Encrypted Text :
Decrypted Text :

Type :	DES RC2 Rijndael TripleDES

codebehind class CryptoForm /******************************************************************/ using System; using System.Collections; using System.ComponentModel; using System.Data; using System.Drawing; using System.Web; using System.Web.SessionState; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.HtmlControls; using System.Security; using System.Security.Cryptography; namespace CSCodeSamples { ///

/// Summary description for CryptoForm. ///

public class CryptoForm : System.Web.UI.Page { protected System.Web.UI.WebControls.Label Label1; protected System.Web.UI.WebControls.Label Label2; protected System.Web.UI.WebControls.Label Label3; protected System.Web.UI.WebControls.Button Button2; protected System.Web.UI.WebControls.HyperLink HyperLink1; protected System.Web.UI.WebControls.Label Label4; protected System.Web.UI.WebControls.Label Label5; protected System.Web.UI.WebControls.RequiredFieldValidator RequiredFieldValidator1; protected System.Web.UI.WebControls.RequiredFieldValidator RequiredFieldValidator2; protected System.Web.UI.WebControls.TextBox txtSample; protected System.Web.UI.WebControls.TextBox txtKey; protected System.Web.UI.WebControls.DropDownList drpType; protected System.Web.UI.WebControls.TextBox txtDecrypt; protected System.Web.UI.WebControls.TextBox txtEncrypt; protected System.Web.UI.WebControls.Label lblTextLength; protected System.Web.UI.WebControls.Label lblKeyLength; protected System.Web.UI.WebControls.Label lblEncryptLength; protected System.Web.UI.WebControls.Label lblDecryptLength; protected System.Web.UI.WebControls.Button Button1; private void Page_Load(object sender, System.EventArgs e) { // Put user code to initialize the page here } #region Web Form Designer generated code override protected void OnInit(EventArgs e) { // // CODEGEN: This call is required by the ASP.NET Web Form Designer. // InitializeComponent(); base.OnInit(e); } ///

/// Required method for Designer support - do not modify /// the contents of this method with the code editor. ///

private void InitializeComponent() { this.Button1.Click += new System.EventHandler(this.Button1_Click); this.Button2.Click += new System.EventHandler(this.Button2_Click); this.Load += new System.EventHandler(this.Page_Load); } #endregion private void Button1_Click(object sender, System.EventArgs e) { // default to DES crypto algorithm CryptoSymmetric objCrypto = new CryptoSymmetric(CryptoSymmetric.EncryptionAlgorithm.DES); switch(drpType.SelectedIndex) { case 0: objCrypto = new CryptoSymmetric(CryptoSymmetric.EncryptionAlgorithm.DES); break; case 1: objCrypto = new CryptoSymmetric(CryptoSymmetric.EncryptionAlgorithm.RC2); break; case 2: objCrypto = new CryptoSymmetric(CryptoSymmetric.EncryptionAlgorithm.Rijndael); break; case 3: objCrypto = new CryptoSymmetric(CryptoSymmetric.EncryptionAlgorithm.TripleDES); break; } txtEncrypt.Text = objCrypto.Encrypt(txtSample.Text, txtKey.Text); DisplayLengths(); } private void Button2_Click(object sender, System.EventArgs e) { // default to DES crypto algorithm CryptoSymmetric objCrypto = new CryptoSymmetric(CryptoSymmetric.EncryptionAlgorithm.DES); switch(drpType.SelectedIndex) { case 0: objCrypto = new CryptoSymmetric(CryptoSymmetric.EncryptionAlgorithm.DES); break; case 1: objCrypto = new CryptoSymmetric(CryptoSymmetric.EncryptionAlgorithm.RC2); break; case 2: objCrypto = new CryptoSymmetric(CryptoSymmetric.EncryptionAlgorithm.Rijndael); break; case 3: objCrypto = new CryptoSymmetric(CryptoSymmetric.EncryptionAlgorithm.TripleDES); break; } txtDecrypt.Text = objCrypto.Decrypt(txtEncrypt.Text, txtKey.Text); DisplayLengths(); } private void DisplayLengths() { lblTextLength.Text = txtSample.Text.Length.ToString(); lblKeyLength.Text = txtKey.Text.Length.ToString(); lblEncryptLength.Text = txtEncrypt.Text.Length.ToString(); lblDecryptLength.Text = txtDecrypt.Text.Length.ToString(); } } }

2 Replies

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meng22y ago
I am writing a encryption and decryption program with C#. This program sends the encrypted message to a unix system, and decrypts the ciphertext from the unix system. According to DES3, the plaintext length is same as ciphertext. But I try many programs on Internet, ciphertext is more than the plaintex. If the plaintext length is 24 bytes, then the ciphertext length is 32bytes. If the plaintext length is 48 bytes, the the ciphertext length is 64 bytes. My key is 24bytes and initial vector(IV) is 8 bytes. I don't know why.
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eyeofdstrm23y ago
Nevermind. I found the issue, and it seems to have fixed my problems (up to this point at least). In the Encrypt method of the CryptoSymmetric class, there was a small piece of code trimming the '\0' bytes, and then returning only a subset of the encrypted byte array. This had the effect of changing the cyphertext, which may or may not have been of a valid length when the object went to decrypt the text. By removing this trim operation, the decrypt method seems to work on anything I encrypt.
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