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C# using Bouncy Castle to PGP Encrypt File causing double encryption?

We are trying to implement PGP encryption into one of our .net apps for the first time at the request of a vendor that we work with. Most of the examples I have found reference using Bouncy Castle so I have attempted to implement that. Everything seems to work fine and I end up with a .pgp file that looks correct. When I send it to the vendor, they say that it appears to be double-encrypted. They said they had to decrypt it twice to read it. Anyone have any ideas what may be going on here? I'll include the sample code that I am using below.
public class Pgp
{
public static void DecryptFile(
string inputFileName,
string keyFileName,
char[] passwd,
string defaultFileName)
{
using (Stream input = File.OpenRead(inputFileName),
keyIn = File.OpenRead(keyFileName))
{
DecryptFile(input, keyIn, passwd, defaultFileName);
}
}
/**
* decrypt the passed in message stream
*/
private static void DecryptFile(
Stream inputStream,
Stream keyIn,
char[] passwd,
string defaultFileName)
{
inputStream = PgpUtilities.GetDecoderStream(inputStream);
try
{
PgpObjectFactory pgpF = new PgpObjectFactory(inputStream);
PgpEncryptedDataList enc;
PgpObject o = pgpF.NextPgpObject();
//
// the first object might be a PGP marker packet.
//
if (o is PgpEncryptedDataList)
{
enc = (PgpEncryptedDataList)o;
}
else
{
enc = (PgpEncryptedDataList)pgpF.NextPgpObject();
}
//
// find the secret key
//
PgpPrivateKey sKey = null;
PgpPublicKeyEncryptedData pbe = null;
PgpSecretKeyRingBundle pgpSec = new PgpSecretKeyRingBundle(
PgpUtilities.GetDecoderStream(keyIn));
foreach (PgpPublicKeyEncryptedData pked in enc.GetEncryptedDataObjects())
{
sKey = PgpExampleUtilities.FindSecretKey(pgpSec, pked.KeyId, passwd);
if (sKey != null)
{
pbe = pked;
break;
}
}
if (sKey == null)
{
throw new ArgumentException("secret key for message not found.");
}
Stream clear = pbe.GetDataStream(sKey);
PgpObjectFactory plainFact = new PgpObjectFactory(clear);
PgpObject message = plainFact.NextPgpObject();
if (message is PgpCompressedData)
{
PgpCompressedData cData = (PgpCompressedData)message;
PgpObjectFactory pgpFact = new PgpObjectFactory(cData.GetDataStream());
message = pgpFact.NextPgpObject();
}
if (message is PgpLiteralData)
{
PgpLiteralData ld = (PgpLiteralData)message;
string outFileName = ld.FileName;
if (outFileName.Length == 0)
{
outFileName = defaultFileName;
}
Stream fOut = File.Create(outFileName);
Stream unc = ld.GetInputStream();
Streams.PipeAll(unc, fOut);
fOut.Close();
}
else if (message is PgpOnePassSignatureList)
{
throw new PgpException("encrypted message contains a signed message - not literal data.");
}
else
{
throw new PgpException("message is not a simple encrypted file - type unknown.");
}
if (pbe.IsIntegrityProtected())
{
if (!pbe.Verify())
{
Console.Error.WriteLine("message failed integrity check");
}
else
{
Console.Error.WriteLine("message integrity check passed");
}
}
else
{
Console.Error.WriteLine("no message integrity check");
}
}
catch (PgpException e)
{
Console.Error.WriteLine(e);
Exception underlyingException = e.InnerException;
if (underlyingException != null)
{
Console.Error.WriteLine(underlyingException.Message);
Console.Error.WriteLine(underlyingException.StackTrace);
}
}
}
public static void EncryptFile(
string outputFileName,
string inputFileName,
string encKeyFileName,
bool armor,
bool withIntegrityCheck)
{
PgpPublicKey encKey = PgpExampleUtilities.ReadPublicKey(encKeyFileName);
using (Stream output = File.Create(outputFileName))
{
EncryptFile(output, inputFileName, encKey, armor, withIntegrityCheck);
}
}
private static void EncryptFile(
Stream outputStream,
string fileName,
PgpPublicKey encKey,
bool armor,
bool withIntegrityCheck)
{
if (armor)
{
outputStream = new ArmoredOutputStream(outputStream);
}
try
{
byte[] bytes = PgpExampleUtilities.CompressFile(fileName, CompressionAlgorithmTag.Zip);
PgpEncryptedDataGenerator encGen = new PgpEncryptedDataGenerator(
SymmetricKeyAlgorithmTag.Cast5, withIntegrityCheck, new SecureRandom());
encGen.AddMethod(encKey);
Stream cOut = encGen.Open(outputStream, bytes.Length);
cOut.Write(bytes, 0, bytes.Length);
cOut.Close();
if (armor)
{
outputStream.Close();
}
}
catch (PgpException e)
{
Console.Error.WriteLine(e);
Exception underlyingException = e.InnerException;
if (underlyingException != null)
{
Console.Error.WriteLine(underlyingException.Message);
Console.Error.WriteLine(underlyingException.StackTrace);
}
}
}
}
public class PgpExampleUtilities
{
/**
* Search a secret key ring collection for a secret key corresponding to keyID if it
* exists.
*
* #param pgpSec a secret key ring collection.
* #param keyID keyID we want.
* #param pass passphrase to decrypt secret key with.
* #return
* #throws PGPException
* #throws NoSuchProviderException
*/
internal static PgpPrivateKey FindSecretKey(PgpSecretKeyRingBundle pgpSec, long keyID, char[] pass)
{
PgpSecretKey pgpSecKey = pgpSec.GetSecretKey(keyID);
if (pgpSecKey == null)
{
return null;
}
return pgpSecKey.ExtractPrivateKey(pass);
}
internal static PgpPublicKey ReadPublicKey(string fileName)
{
using (Stream keyIn = File.OpenRead(fileName))
{
return ReadPublicKey(keyIn);
}
}
internal static PgpPublicKey ReadPublicKey(Stream input)
{
PgpPublicKeyRingBundle pgpPub = new PgpPublicKeyRingBundle(
PgpUtilities.GetDecoderStream(input));
//
// we just loop through the collection till we find a key suitable for encryption, in the real
// world you would probably want to be a bit smarter about this.
//
foreach (PgpPublicKeyRing keyRing in pgpPub.GetKeyRings())
{
foreach (PgpPublicKey key in keyRing.GetPublicKeys())
{
if (key.IsEncryptionKey)
{
return key;
}
}
}
throw new ArgumentException("Can't find encryption key in key ring.");
}
internal static byte[] CompressFile(string fileName, CompressionAlgorithmTag algorithm)
{
MemoryStream bOut = new MemoryStream();
PgpCompressedDataGenerator comData = new PgpCompressedDataGenerator(algorithm);
PgpUtilities.WriteFileToLiteralData(comData.Open(bOut), PgpLiteralData.Binary,
new FileInfo(fileName));
comData.Close();
return bOut.ToArray();
}
}
public class Streams
{
private const int BufferSize = 512;
public static void PipeAll(Stream inStr, Stream outStr)
{
byte[] bs = new byte[BufferSize];
int numRead;
while ((numRead = inStr.Read(bs, 0, bs.Length)) > 0)
{
outStr.Write(bs, 0, numRead);
}
}
}
}
I then call the EncryptFile Method as below:
public void EncryptMyFile()
{
Pgp.EncryptFile(#"C:\ ... Output.pgp", #"C:\ ... Input.txt", #"C:\ ... pubkey.txt", false, false);
}
Used code above and it properly generated a file, but the vendor says that it is "double encrypted".

Decryption Exception - length of the data to decrypt is invalid When add more data

I am trying to decrypt that from the database. The Data is encrypted from the SQL Server
reportItems.DisabilityGroup = Cryptography.ASPEncrypter(reportItems.DisabilityGroup, true);
The above code is when I invoke the decryption method. It works for small data but fails for more data. I get the following order
System.Security.Cryptography.CryptographicException: 'Length of the data to decrypt is invalid.'
private static string DoEncrypt(string Message)
{
// Encrypt string
byte[] Results;
var UTF8 = new UTF8Encoding();
using (var HashProvider = new MD5CryptoServiceProvider())
{
var TDESKey = HashProvider.ComputeHash(UTF8.GetBytes(PassPhrase));
//var TDESAlgorithm = new TripleDESCryptoServiceProvider()
//{
// Key = TDESKey,
// Mode = CipherMode.ECB,
// Padding = PaddingMode.PKCS7
//};
using (var TDESAlgorithm = new TripleDESCryptoServiceProvider())
{
TDESAlgorithm.Key = TDESKey;
TDESAlgorithm.Mode = CipherMode.ECB;
TDESAlgorithm.Padding = PaddingMode.PKCS7;
if (Message == null)
return "";
var DataToEncrypt = UTF8.GetBytes(Message);
try
{
var Encryptor = TDESAlgorithm.CreateEncryptor();
Results = Encryptor.TransformFinalBlock(DataToEncrypt, 0, DataToEncrypt.Length);
}
finally
{
TDESAlgorithm.Clear();
HashProvider.Clear();
}
}
}
return Convert.ToBase64String(Results);
}
private static string DoDecrypt(string Message)
{
// Decrypt string
byte[] Results;
var UTF8 = new UTF8Encoding();
using (var HashProvider = new MD5CryptoServiceProvider())
{
var TDESKey = HashProvider.ComputeHash(UTF8.GetBytes(PassPhrase));
using (var TDESAlgorithm = new TripleDESCryptoServiceProvider())
{
TDESAlgorithm.Key = TDESKey;
TDESAlgorithm.Mode = CipherMode.ECB;
TDESAlgorithm.Padding = PaddingMode.PKCS7;
//var DataToDecrypt = Convert.FromBase64String(Message);
var DataToDecrypt = new byte[0];
if (!IsBase64String(Message, out DataToDecrypt))
{
return Message;
}
try
{
var Decryptor = TDESAlgorithm.CreateDecryptor();
Results = Decryptor.TransformFinalBlock(DataToDecrypt, 0, DataToDecrypt.Length);
}
finally
{
TDESAlgorithm.Clear();
HashProvider.Clear();
}
}
}
return UTF8.GetString(Results);
}
public static bool IsBase64String(string base64String, out byte[] bytes)
{
bytes = null;
if (string.IsNullOrEmpty(base64String) || base64String.Length % 4 != 0
|| base64String.Contains(" ") || base64String.Contains("\t") || base64String.Contains("\r") || base64String.Contains("\n"))
return false;
try
{
bytes = Convert.FromBase64String(base64String);
return true;
}
catch (Exception)
{
// Handle the exception
}
return false;
}
public static string ASPEncrypter(string PriorValue, bool Decrypt)
{
// Public function to encrypt/decrypt string
if (String.IsNullOrWhiteSpace(PriorValue))
return "";
var Result = string.Empty;
if (Decrypt)
Result = DoDecrypt(PriorValue);
else
Result = DoEncrypt(PriorValue);
return Result;
}

RSA.Cryptography "Incorrect Parameter" thrown C#

I'm trying to set up a messing server for me and my friends and I ran into issues with RSA Decryption.
The correct keys are used
If I enable OAEP padding I get a error that simply states "OAEPpadding"
I'm losing my mind on this bug, I'm posting the script below.
Encryption works fine, its just decryption that's problematic
Please Help
using System;
using System.Net.Sockets;
using System.Net;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
using System.Security.Cryptography;
using System.Xml.Serialization;
namespace Server_WIN_
{
class Program
{
public static XmlSerializer xs = new XmlSerializer(typeof(RSAParameters));
public static TcpListener server = new TcpListener(IPAddress.Parse("192.168.1.93"), 78);
public static TcpClient client = null;
public static NetworkStream canwetalk = null;
public static RSACryptoServiceProvider csp = new RSACryptoServiceProvider(4096);
public static RSAParameters publickey;
public static RSAParameters privatekey;
static Program()
{
server.Start();
csp.PersistKeyInCsp = false;
publickey = csp.ExportParameters(false);
privatekey = csp.ExportParameters(true);
client = server.AcceptTcpClient();
canwetalk = client.GetStream();
}
public static void Main(string[] args)
{
string strHostName = "";
strHostName = Dns.GetHostName();
// Then using host name, get the IP address list..
IPHostEntry ipEntry = Dns.GetHostEntry(strHostName);
IPAddress[] addr = ipEntry.AddressList;
Random ran = new Random();
HashAlgorithm sha = SHA256.Create();
string msg = "";
byte[] buffer = new byte[4096];
msg = "test";
msg = Encrypt(msg);
msg = Decrypt(msg);
Console.WriteLine(msg);
}
public static string PublicKeyString()
{
byte[] bytes = new byte[4096];
var sw = new StringWriter();
var xs = new XmlSerializer(typeof(RSAParameters));
xs.Serialize(sw, publickey);
return sw.ToString();
}
public static string PrivateKeyString()
{
byte[] bytes = new byte[4096];
var sw = new StringWriter();
var xs = new XmlSerializer(typeof(RSAParameters));
xs.Serialize(sw, privatekey);
return sw.ToString();
}
public static string Encrypt(string msg)
{
csp.ImportParameters(publickey);
byte[] data = System.Text.Encoding.ASCII.GetBytes(msg);
byte[] cipher = csp.Encrypt(data, false);
return System.Text.Encoding.ASCII.GetString(cipher);
}
public static string Decrypt(string msg)
{
try
{
csp.ImportParameters(privatekey);
byte[] decrypted = csp.Decrypt(System.Text.Encoding.ASCII.GetBytes(msg), false);
return System.Text.Encoding.Unicode.GetString(decrypted);
}
catch(CryptographicException e)
{
string p = e.ToString();
Console.WriteLine(p);
}
return "";
}
public static void ExportPublicKey()
{
string msg = PublicKeyString();
byte[] buffer = new byte[4096];
byte[] msg1 = System.Text.Encoding.ASCII.GetBytes(msg);
canwetalk.Write(msg1, 0, msg1.Length);
}
public static void ToStream(string msg, bool Encryption)
{
if (Encryption)
{
msg = Encrypt(msg);
byte[] msgbytes = System.Text.Encoding.ASCII.GetBytes(msg);
canwetalk.Write(msgbytes, 0, msgbytes.Length);
}
else
{
byte[] msgbytes = System.Text.Encoding.ASCII.GetBytes(msg);
canwetalk.Write(msgbytes, 0, msgbytes.Length);
}
}
public static string ReadStream()
{
byte[] buffer = new byte[4096];
int i = canwetalk.Read(buffer,0,buffer.Length);
return System.Text.Encoding.ASCII.GetString(buffer,0,i);
}
}

You can find this stackoverflow question helpful, but it's quite out of date Error occurred while decoding OAEP padding

Don't use the same provider. Do this instead:
var publicKey = RSA.Create();
publicKey.ImportParameters(PUB_PARAMS);
var privateKey = RSA.Create();
privateKey.ImportParameters(PRIV_PARAMS);

PDF Signature - Embed separatly signed hash

I am trying to sign a PDF Document using two web services in two servers. But it is showing "Document has been altered or corrupt since it was signed" in Adobe Reader. Can anybody suggest what is wrong in following code.
PROCEDURE
1. Web service (WS) on Server A, Generate hash from PDF and sent to WS on Server B for signing.
2. WS on Server B signs hash.
3. WS on Server A receives signed hash and Embed in PDF document.
CODE
GENERATE HASH
private PDFHashData generateHash(byte[] content, string userName)
{
PdfReader reader = new PdfReader(content);
MemoryStream ms = new MemoryStream();
PdfStamper stamper = PdfStamper.CreateSignature(reader, ms, '\0');
PdfSignatureAppearance appearance = stamper.SignatureAppearance;
appearance.SetVisibleSignature(new Rectangle(500, 150, 400, 200), 1, signatureFieldName);
appearance.SignDate = DateTime.Now;
appearance.Reason = Reason;
appearance.Location = Location;
appearance.Contact = Contact;
StringBuilder buf = new StringBuilder();
buf.Append("Digitally signed by");
buf.Append("\n");
buf.Append(userName);
buf.Append("\n");
buf.Append("Date: " + appearance.SignDate);
appearance.Layer2Text = buf.ToString();
appearance.Acro6Layers = true;
appearance.CertificationLevel = 0;
IExternalSignatureContainer external = new ExternalBlankSignatureContainer(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED);
MakeSignature.SignExternalContainer(appearance, external, 8192);
byte[] hash = SHA256Managed.Create().ComputeHash(appearance.GetRangeStream());
StringBuilder hex = new StringBuilder(hash.Length * 2);
foreach (byte b in hash)
hex.AppendFormat("{0:x2}", b);
PDFHashData phData= new PDFHashData();
phData.Hash = hex.ToString();
phData.Content = Convert.ToBase64String(ms.ToArray());
return phData;
}
SIGN HASH
byte[] StringToByteArray(string hex)
{
return Enumerable.Range(0, hex.Length)
.Where(x => x % 2 == 0)
.Select(x => Convert.ToByte(hex.Substring(x, 2), 16))
.ToArray();
}
private Stream getCertificate()
{
// Base 64 byte - PFX file with private key
return new MemoryStream(Convert.FromBase64String("..................................AgIEAA=="));
}
protected void Page_Load(object sender, EventArgs e)
{
Stream stream = Request.InputStream;
byte[] buffer = new byte[stream.Length];
stream.Read(buffer, 0, buffer.Length);
byte[] hash = StringToByteArray(Encoding.UTF8.GetString(buffer));
Pkcs12Store store = new Pkcs12Store(getCertificate(), "*******".ToCharArray());
String alias = "";
foreach (string al in store.Aliases)
if (store.IsKeyEntry(al) && store.GetKey(al).Key.IsPrivate)
{
alias = al;
break;
}
AsymmetricKeyEntry pk = store.GetKey(alias);
X509CertificateEntry[] chain = store.GetCertificateChain(alias);
List<Org.BouncyCastle.X509.X509Certificate> c = new List<Org.BouncyCastle.X509.X509Certificate>();
foreach (X509CertificateEntry en in chain)
{
c.Add(en.Certificate);
}
PrivateKeySignature signature = new PrivateKeySignature(pk.Key, "SHA1");
String hashAlgorithm = signature.GetHashAlgorithm();
PdfPKCS7 sgn = new PdfPKCS7(null, c, hashAlgorithm, false);
DateTime signingTime = DateTime.Now;
byte[] sh = sgn.getAuthenticatedAttributeBytes(hash, null, null, CryptoStandard.CMS);
byte[] extSignature = signature.Sign(sh);
sgn.SetExternalDigest(extSignature, null, signature.GetEncryptionAlgorithm());
Response.Write(Convert.ToBase64String(sgn.GetEncodedPKCS7(hash, null, null, null, CryptoStandard.CMS)));
}
EMBED SIGNATURE TO PDF
private byte[] signPDF(byte[] content, string userName, byte[] pk)
{
PdfReader reader = new PdfReader(content);
MemoryStream os = new MemoryStream();
IExternalSignatureContainer external = new MyExternalSignatureContainer(pk);
MakeSignature.SignDeferred(reader, signatureFieldName, os, external);
return os.ToArray();
}

For those who are interested I am posting the answer.
I ended up using itextsharp 5.5.10. Code is given below,
Initialize PDF object
public PDFSigning(byte[] Content, string UserName)
{
content = Content;
reader = new PdfReader(content);
ms = new MemoryStream();
stamper = PdfStamper.CreateSignature(reader, ms, '\0');
appearance = stamper.SignatureAppearance;
userName = UserName;
}
private Stream getCertificate()
{
return new MemoryStream(Convert.FromBase64String("************************=="));
}
Generate hash
private string generateHash()
{
appearance.SetVisibleSignature(new Rectangle(500, 150, 400, 200), 1, signatureFieldName);
appearance.SignDate = DateTime.Now;
appearance.Reason = Reason;
appearance.Location = Location;
appearance.Contact = Contact;
StringBuilder buf = new StringBuilder();
buf.Append("Digitally signed by");
buf.Append("\n");
buf.Append(userName);
buf.Append("\n");
buf.Append("Date: " + appearance.SignDate);
appearance.Layer2Text = buf.ToString();
appearance.Acro6Layers = true;
appearance.CertificationLevel = 0;
PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED)
{
Date = new PdfDate(appearance.SignDate),
Name = userName
};
dic.Reason = appearance.Reason;
dic.Location = appearance.Location;
dic.Contact = appearance.Contact;
appearance.CryptoDictionary = dic;
Dictionary<PdfName, int> exclusionSizes = new Dictionary<PdfName, int>();
exclusionSizes.Add(PdfName.CONTENTS, (csize * 2) + 2);
appearance.PreClose(exclusionSizes);
HashAlgorithm sha = new SHA256CryptoServiceProvider();
Stream s = appearance.GetRangeStream();
int read = 0;
byte[] buff = new byte[0x2000];
while ((read = s.Read(buff, 0, 0x2000)) > 0)
{
sha.TransformBlock(buff, 0, read, buff, 0);
}
sha.TransformFinalBlock(buff, 0, 0);
StringBuilder hex = new StringBuilder(sha.Hash.Length * 2);
foreach (byte b in sha.Hash)
hex.AppendFormat("{0:x2}", b);
return hex.ToString();
}
Sign hash
public byte[] SignMsg(string hexhash)
{
byte[] hash = hexToByteArray(hexhash);
Pkcs12Store store = new Pkcs12Store(getCertificate(), "*********".ToCharArray());
String alias = "";
foreach (string al in store.Aliases)
if (store.IsKeyEntry(al) && store.GetKey(al).Key.IsPrivate)
{
alias = al;
break;
}
AsymmetricKeyEntry pk = store.GetKey(alias);
X509CertificateEntry[] chain = store.GetCertificateChain(alias);
List<Org.BouncyCastle.X509.X509Certificate> c = new List<Org.BouncyCastle.X509.X509Certificate>();
foreach (X509CertificateEntry en in chain)
{
c.Add(en.Certificate);
}
PrivateKeySignature signature = new PrivateKeySignature(pk.Key, "SHA256");
String hashAlgorithm = signature.GetHashAlgorithm();
PdfPKCS7 sgn = new PdfPKCS7(null, c, hashAlgorithm, false);
DateTime signingTime = DateTime.Now;
byte[] sh = sgn.getAuthenticatedAttributeBytes(hash, null, null, CryptoStandard.CMS);
byte[] extSignature = signature.Sign(sh);
sgn.SetExternalDigest(extSignature, null, signature.GetEncryptionAlgorithm());
return sgn.GetEncodedPKCS7(hash, null, null, null, CryptoStandard.CMS);
}
Sign PDF
private byte[] signPDF(byte[] pk)
{
byte[] paddedSig = new byte[csize];
System.Array.Copy(pk, 0, paddedSig, 0, pk.Length);
PdfDictionary dic2 = new PdfDictionary();
dic2.Put(PdfName.CONTENTS, new PdfString(paddedSig).SetHexWriting(true));
appearance.Close(dic2);
//System.IO.File.WriteAllBytes(System.Web.HttpContext.Current.Server.MapPath("~/temp.pdf"), ms.ToArray());
return ms.ToArray();
}

Hybrid cryptography. Length of the data to decrypt is invalid

I am getting above mentioned error during a hybrid cryptography implementation.
as per https://en.wikipedia.org/wiki/Hybrid_cryptosystem
I am just stucked at the last step
My code is
private void button1_Click(object sender, EventArgs e)
{
try
{
CspParameters cspParams = new CspParameters { ProviderType = 1 };
RSACryptoServiceProvider rsaProvider = new RSACryptoServiceProvider(2048, cspParams);
string publicKey =lblPublicKey.Text = Convert.ToBase64String(rsaProvider.ExportCspBlob(false));
string privateKey = lblPrivateKey.Text= Convert.ToBase64String(rsaProvider.ExportCspBlob(true));
string symmericKey = txtBoxSymmetricKey.Text = "Kamran12";
txtEncryptedData.Text = EncryptData(txtInputData.Text, symmericKey);
txtBoxEncryptedSymmetricKey.Text = RSA_Encrypt(symmericKey, publicKey);
txtBoxDescryptedSymmetricKey.Text = RSA_Decrypt(txtBoxEncryptedSymmetricKey.Text, privateKey);
txtDecryptedData.Text = DecryptData(txtEncryptedData.Text, txtBoxDescryptedSymmetricKey.Text); //getting error length of the data to decrypt is invalid
}
catch (Exception exc)
{
}
}
public static string RSA_Decrypt(string encryptedText, string privateKey)
{
CspParameters cspParams = new CspParameters { ProviderType = 1 };
RSACryptoServiceProvider rsaProvider = new RSACryptoServiceProvider(cspParams);
rsaProvider.ImportCspBlob(Convert.FromBase64String(privateKey));
var buffer = Convert.FromBase64String(encryptedText);
byte[] plainBytes = rsaProvider.Decrypt(buffer, false);
string plainText = Encoding.UTF8.GetString(plainBytes, 0, plainBytes.Length);
return plainText;
}
public static string RSA_Encrypt(string data, string publicKey)
{
CspParameters cspParams = new CspParameters { ProviderType = 1 };
RSACryptoServiceProvider rsaProvider = new RSACryptoServiceProvider(cspParams);
rsaProvider.ImportCspBlob(Convert.FromBase64String(publicKey));
byte[] plainBytes = Encoding.UTF8.GetBytes(data);
byte[] encryptedBytes = rsaProvider.Encrypt(plainBytes, false);
return Convert.ToBase64String(encryptedBytes);
}
public string EncryptData(string data, string key)
{
string encryptedData = null;
byte[] buffer = Encoding.UTF8.GetBytes(data);
DESCryptoServiceProvider desCryptSrvckey = new DESCryptoServiceProvider
{
Key = new UTF8Encoding().GetBytes(key)
};
desCryptSrvckey.IV = desCryptSrvckey.Key;
using (MemoryStream stmCipherText = new MemoryStream())
{
using (CryptoStream cs = new CryptoStream(stmCipherText, desCryptSrvckey.CreateEncryptor(), CryptoStreamMode.Write))
{
cs.Write(buffer, 0, buffer.Length);
cs.FlushFinalBlock();
encryptedData = Encoding.UTF8.GetString(stmCipherText.ToArray());
}
}
return encryptedData;
}
public string DecryptData(string data, string key)
{
byte[] encryptedMessageBytes = Encoding.UTF8.GetBytes(data);
string decryptedData = null;
DESCryptoServiceProvider desCryptSrvckey = new DESCryptoServiceProvider
{
Key = new UTF8Encoding().GetBytes(key)
};
desCryptSrvckey.IV = desCryptSrvckey.Key;
using (MemoryStream encryptedStream = new MemoryStream(encryptedMessageBytes))
{
using (
CryptoStream cs = new CryptoStream(encryptedStream, desCryptSrvckey.CreateDecryptor(),
CryptoStreamMode.Read))
{
using (StreamReader sr = new StreamReader(cs))
{
decryptedData = sr.ReadToEnd();
}
}
}
return decryptedData;
}

You declare encryptedData as a string. This is incorrect. Your encrypted data is bytes, not a character string. Attempting to convert raw bytes to UTF-8 text, as in encryptedData = Encoding.UTF8.GetString(stmCipherText.ToArray()); will not result in UTF-8 text but give you garbage and possibly lose data.
If you want the output from your encryption to be as text, then take the cyphertext bytes and use Convert.ToBase64String() to turn them into a text string.
When decrypting, convert the Base64 string back into bytes and decrypt the bytes.