We Keep Coding

How to encrypt with iOS CryptoKit and decrypt with C# in NetCore

I would like to encrypt data in iOS app with a SymetricKey and the CryptoKit and decrypt on server side with C# in Net Core.
iOS code:
class Security {
static let keyStr = "d5a423f64b607ea7c65b311d855dc48f" //32
static let iv="31348c0987c7" //12
class func encode(_ text:String)->String {
let key=SymmetricKey(data: Security.keyStr.data(using: .utf8)!)
let nonce=try! AES.GCM.Nonce(data: iv.data(using: .utf8)!)
let encrypted=try! AES.GCM.seal(text.data(using: .utf8)!, using: key, nonce: nonce)
return encrypted.combined!.base64EncodedString()
}
}
I pass the result of the encryption to my backend and I would like to decrypt
C# Code:
public string decrypt(string encryptedText)
{
string keyStr = "d5a423f64b607ea7c65b311d855dc48f";
string iv = "31348c0987c7";
string plaintext = "";
Debug.WriteLine(encryptedText);
using (Aes aesAlg = Aes.Create())
{
Debug.WriteLine(AesGcm.IsSupported);
var key = System.Text.Encoding.UTF8.GetBytes(keyStr);
var iV = System.Text.Encoding.UTF8.GetBytes(iv);
aesAlg.Key = key;
aesAlg.IV = iV;
// Create a decryptor to perform the stream transform.
ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
// Create the streams used for decryption.
using (MemoryStream msDecrypt = new MemoryStream(Convert.FromBase64String(request.pswd)))
{
using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
{
using (StreamReader srDecrypt = new StreamReader(csDecrypt))
{
// Read the decrypted bytes from the decrypting stream
// and place them in a string.
plaintext = srDecrypt.ReadToEnd();
}
}
}
}
Debug.WriteLine(plaintext);
}
So for example word: Test gets encrypted as: MzEzNDhjMDk4N2M3CI68IDEJeBR4OFtWO3GPO3TIgos=
When I get to line:
aesAlg.IV = iV;
I get an error "Specified initialization vector (IV) does not match the block size for this algorithm."
It seems as if C# needs byte[16], but in iOS I seem to be stuck with 12.
I got stuck at this point. Any idea greately appreciated.
Thank you.

The posted Swift code applies AES in GCM mode, s. AES.GCM. The posted C# code also uses AES, however not the GCM mode, but the default CBC mode (s. Aes, Mode).
The CBC mode applies a 16 bytes IV, while the GCM mode uses a 12 bytes nonce. That is what the error message is pointing to.
For successful decryption, AES in GCM mode must also be used on the C# side. In .NET AES in GCM mode is supported with the AesGcm class (as of .NET Core 3.0).
Note also that the data given by the Swift code is the Base64 encoding of the concatenation of 12 bytes nonce, ciphertext and 16 bytes tag (in that order), which must be separated in the C# code, where the portions are processed individually.
A possible C# implementation that decrypts the ciphertext generated by the posted Swift code is:
byte[] nonceCiphertextTag = Convert.FromBase64String("MzEzNDhjMDk4N2M3CI68IDEJeBR4OFtWO3GPO3TIgos=");
byte[] key = Encoding.UTF8.GetBytes("d5a423f64b607ea7c65b311d855dc48f");
Span<byte> nonceCiphertextTagSpan = nonceCiphertextTag.AsSpan();
Span<byte> nonce = nonceCiphertextTagSpan[..12];
Span<byte> ciphertext = nonceCiphertextTagSpan[12..^16];
Span<byte> tag = nonceCiphertextTagSpan[^16..];
byte[] plaintext = new byte[ciphertext.Length];
using AesGcm aesGcm = new AesGcm(key);
aesGcm.Decrypt(nonce, ciphertext, tag, plaintext); // throws an 'CryptographicException: The computed authentication tag did not match the input authentication tag' if authentication fails
Console.WriteLine(Encoding.UTF8.GetString(plaintext)); // Test
Edit: An alternative to the native .NET class AesGcm is C#/BouncyCastle. Maybe this is supported in your environment:
using Org.BouncyCastle.Crypto.Engines;
using Org.BouncyCastle.Crypto.Modes;
using Org.BouncyCastle.Crypto.Parameters;
...
byte[] nonceCiphertextTag = Convert.FromBase64String("MzEzNDhjMDk4N2M3CI68IDEJeBR4OFtWO3GPO3TIgos=");
byte[] key = Encoding.UTF8.GetBytes("d5a423f64b607ea7c65b311d855dc48f");
Span<byte> nonceCiphertextTagSpan = nonceCiphertextTag.AsSpan();
byte[] nonce = nonceCiphertextTagSpan[..12].ToArray();
byte[] ciphertextTag = nonceCiphertextTagSpan[12..].ToArray();
GcmBlockCipher gcmBlockCipher = new GcmBlockCipher(new AesEngine());
AeadParameters aeadParameters = new AeadParameters(new KeyParameter(key), 128, nonce);
gcmBlockCipher.Init(false, aeadParameters);
byte[] plaintext = new byte[gcmBlockCipher.GetOutputSize(ciphertextTag.Length)];
int length = gcmBlockCipher.ProcessBytes(ciphertextTag, 0, ciphertextTag.Length, plaintext, 0);
gcmBlockCipher.DoFinal(plaintext, length); // throws an 'InvalidCipherTextException: mac check in GCM failed' if authentication fails
Console.WriteLine(Encoding.UTF8.GetString(plaintext)); // Test
Note that unlike the native AesGcm class, C#/BouncyCastle requires the concatenation of ciphertext and tag, so only the nonce needs to be separated.

Getting error Length of the data to decrypt is invalid [duplicate]

I am working in a C# application. We have common methods to store data on a file. These methods encrypt the data and store them on the file system. when we need the data, ReadData method decrypts the data and returns me plain text.
This code works fine in normal cases if size of the text in small. but for a example text given below, the decryption code is throwing exception - length of the data to decrypt is invalid.
The exception occurs at line
// close the CryptoStream
x_cryptostream.Close();
I tried different ways but no luck. Can some pls help.
Why am I encrypting already encrypted data - I am just trying to store in a file using common method of the huge application. The common methods storedata(key,data) nad readdata(key) do the encryption/decryption I can't avoid.
public static byte[] Decrypt(byte[] ciphertext, string Key, string IV)
{
byte[] k = Encoding.Default.GetBytes(Key);
byte[] iv = Encoding.Default.GetBytes(IV);
// create the encryption algorithm
SymmetricAlgorithm x_alg = SymmetricAlgorithm.Create("Rijndael");
x_alg.Padding = PaddingMode.PKCS7;
// create an ICryptoTransform that can be used to decrypt data
ICryptoTransform x_decryptor = x_alg.CreateDecryptor(k, iv);
// create the memory stream
MemoryStream x_memory_stream = new MemoryStream();
// create the CryptoStream that ties together the MemoryStream and the
// ICryptostream
CryptoStream x_cryptostream = new CryptoStream(x_memory_stream,
x_decryptor, CryptoStreamMode.Write);
// write the ciphertext out to the cryptostream
x_cryptostream.Write(ciphertext, 0, ciphertext.Length);
// close the CryptoStream
x_cryptostream.Close();
// get the plaintext from the MemoryStream
byte[] x_plaintext = x_memory_stream.ToArray();
Below is the code of encrypt method.
public static byte[] Encrypt(string strplain, string Key, string IV)
{
byte[] k = Encoding.Default.GetBytes(Key);
byte[] iv = Encoding.Default.GetBytes(IV);
byte[] plaintext = Encoding.Default.GetBytes(strplain);
// create the encryption algorithm
SymmetricAlgorithm x_alg = SymmetricAlgorithm.Create("Rijndael");
x_alg.Padding = PaddingMode.PKCS7;
// create an ICryptoTransform that can be used to encrypt data
ICryptoTransform x_encryptor = x_alg.CreateEncryptor(k, iv);
// create the memory stream
MemoryStream x_memory_stream = new MemoryStream();
// create the CryptoStream that ties together the MemoryStream and
// the ICryptostream
CryptoStream x_cryptostream = new CryptoStream(x_memory_stream,
x_encryptor, CryptoStreamMode.Write);
// write the plaintext out to the cryptostream
x_cryptostream.Write(plaintext, 0, plaintext.Length);
// close the CryptoStream
x_cryptostream.Close();
// get the ciphertext from the MemoryStream
byte[] x_ciphertext = x_memory_stream.ToArray();
// close memory stream
x_memory_stream.Close();
// convert from array to string
string cipher_Tx = Encoding.Default.GetString(x_ciphertext,
0, x_ciphertext.Length);
x_encryptor.Dispose();
x_alg.Clear();
byte[] cipher = Encoding.Default.GetBytes(cipher_Tx);
return cipher;
}

Your problem is string cipher_Tx = Encoding.Default.GetString(x_ciphertext, 0, x_ciphertext.Length);.
x_ciphertext is not a valid byte representation of text, it has many unpresentable characters and when you do your byte[] to string conversion you are losing information. The correct way to do it is use a string format that is designed to represent binary data using something like Convert.ToBase64String(byte[]) and Convert.FromBase64String(string).
string cipher_Tx = Convert.ToBase64String(x_ciphertext)
x_encryptor.Dispose();
x_alg.Clear();
byte[] cipher = Convert.FromBase64String(cipher_Tx)
That being said, there is a lot of other "odd" things about your code, for example you don't use using statements and you really should. Also that whole conversion to string and back is totally unnecessary, just return x_ciphertext. There may be other problems with the code too (like where did the strings for Key and IV come from) and many other best practices (like you should be generating a random IV and writing it out in to the output and the key should be generated using a key derivation function not straight from user text), but I stopped checking after I found the string conversion issue.

Your code above works as long as the key and iv used to decrypt match the key and iv used to encrypt. Try this:
byte[] test = new byte[1000000];
for (int i = 0; i < 256; i++)
{
test[i] = (byte)i;
}
var ciphertext = Encrypt(Encoding.Default.GetString(test), "0000000000000000", "0000000000000000");
byte[] check = Decrypt(ciphertext, "0000000000000000", "0000000000000000");
for (int i = 0; i < 256; i++)
{
Debug.Assert(check[i] == (byte)i, "round trip");
}
As you can see, one million bytes encrypt and decrypt just fine with your code, so I don't think it has anything to do with data size.
However, change the IV like this:
byte[] check = Decrypt(ciphertext, "0000000000000000", "000000000000000X"); // note X
and the Debug.Assert will fire -- the decryption will not match. However, x_cryptostream.Close() succeeds.
Next, try changing the key like this:
byte[] check = Decrypt(ciphertext, "000000000000000X", "0000000000000000"); // note X
Now, x_cryptostream.Close() will fail with a CryptographicException, probably, "Padding is invalid and cannot be removed."
Corrupting the key will cause the decryption to fail, and x_cryptostream.Close() to fail.
I think the problem is in your saving and later restoring the key bytes.
BTW: Hopefully you are using the full binary range of the key, and not basing it only on ASCII characters, otherwise you don't really have a strong key.

Sending encrypted data via TCP (“Bad Data” exception)

How can i send illegal charecters from tpc client to tcp server.
This is an example of what the encrypted gibberish looks like:
https://i.stack.imgur.com/wfZdm.png
How can i send this pice of gibberish to either my client or server?
This is my encryption & decryption code
public static string Decrypt(string data)
{
byte[] dataToDecrypt = StringToByteArray(data);
byte[] decryptedData;
using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
{
rsa.FromXmlString(privateKey);
decryptedData = rsa.Decrypt(dataToDecrypt, false);
}
UnicodeEncoding byteConverter = new UnicodeEncoding();
return ByteArrayToString(decryptedData);
}
public static string Encrypt(string data, string publicKey)
{
UnicodeEncoding byteConverter = new UnicodeEncoding();
byte[] dataToEncrypt = StringToByteArray(data);
byte[] encryptedData;
using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
{
rsa.FromXmlString(publicKey);
encryptedData = rsa.Encrypt(dataToEncrypt, false);
}
return ByteArrayToString(encryptedData);
}
public static byte[] StringToByteArray(string data)
{
return Encoding.ASCII.GetBytes(data);
}
public static string ByteArrayToString(byte[] bytes)
{
return Encoding.ASCII.GetString(bytes);
}
I have made it so the client and the server share eachothers public keys but i am getting Exception "Bad data". One more thing if i send encrypted data from a client to the server which data is 128 bytes the server receives only 78 bytes for example

There's a few things wrong with your code:
You shouldn't be using String at all.
String is meant for text, not arbitrary binary data (I assume you got this impression from C or PHP where their string types are really just synonyms for - or thin-wrappers over - a byte-array).
Keep the Byte[] buffer you get from rs.Encrypt and pass that directly to your Socket, TcpClient or NetworkStream that you're using. You'll need to define a binary protocol with length-prefix though.
Encoding.ASCII.GetBytes will convert the UTF-16LE-encoded characters in the String data instance to 7-bit ASCII, it does this by replacing characters with values above 0x7F with '?' - this is not what you want! (and this is what's causing the garbage output on your screen: those "illegal characters" are byte-values above 0x7F that are outside ASCII's 7-bit range. From the documentation:
It uses replacement fallback to replace each string that it cannot encode and each byte that it cannot decode with a question mark ("?") character.
If you really do want to transmit data over the network using human-readable text then use Base64 encoding: Convert.ToBase64String( Byte[] buffer ) and convert it back using Convert.FromBase64String( String s ) at the receiving end - but you'll still need to length-prefix or delimit your data.

Creating Encryption Using string

Hi I'm just trying to encrypt a string but i want to reverse the decryption method to create exactly encrypted key
decryption was
public string newSample(string s)
{
byte[] buffer = Convert.FromBase64String(s);
Encoding utF8 = Encoding.UTF8;
byte[] bytes1 = utF8.GetBytes("key1");
byte[] bytes2 = utF8.GetBytes("key2");
RijndaelManaged rijndaelManaged1 = new RijndaelManaged();
rijndaelManaged1.Mode = CipherMode.CBC;
rijndaelManaged1.Padding = PaddingMode.Zeros;
rijndaelManaged1.BlockSize = 128;
rijndaelManaged1.KeySize = 128;
RijndaelManaged rijndaelManaged2 = rijndaelManaged1;
ICryptoTransform transform = (ICryptoTransform)null;
transform = rijndaelManaged2.CreateDecryptor(bytes2, bytes1);
byte[] bytes3 = (byte[])null;
using (MemoryStream memoryStream = new MemoryStream())
{
using (CryptoStream cryptoStream = new CryptoStream((Stream)memoryStream, transform, CryptoStreamMode.Write))
{
cryptoStream.Write(buffer, 0, buffer.GetLength(0));
cryptoStream.FlushFinalBlock();
}
rijndaelManaged2.Clear();
bytes3 = memoryStream.ToArray();
}
return new string(Encoding.UTF8.GetChars(bytes3));
}
is it possible to reverse the code and create encryption key ? if so
how could be the encryption should look lik for this decryption method ??
thanks

This is the problem - or at least the initial problem:
return new string(Encoding.UTF8.GetChars(bytes3));
The result of encryption is not a UTF-8-encoded byte array... it's arbitrary bytes. By assuming it's valid UTF-8-encoded text, you're losing information.
Instead, you should use a hex or base64 approach, both of which are designed to convert arbitrary binary data to text in a lossless fashion. For example:
return Convert.ToBase64String(bytes3);
Now, your decryption code should start with:
byte[] encryptedData = Convert.FromBase64String(base64EncryptedText);
(Where base64EncryptedText is the value returned from your encryption method.)
From there, it should be a matter of just reversing each step, and there are numerous examples around. You may well find that you've got a problem due to the padding mode, however - you may need to separately record the length of the original data.
As an aside, it's not clear why your method takes a string in the first place. It's odd for an encryption method to take a base64-encoded piece of data. It's more common for it to take either a normal plain text string which is converted into bytes using something like Encoding.UTF8, or for it to take a byte[] to start with.

How to decrypt AesCryptoServiceProvider using JavaScript?

I am using EncryptStringToBytes_Aes method from MSDN to encrypt some data using custom passphrase like this:
string original = "some data to encrypt";
byte[] encrypted;
using (AesManaged aes = new AesManaged())
{
// Prepare new Key and IV.
string passphrase = "somepassphrase";
byte[] saltArray = Encoding.ASCII.GetBytes("somesalt");
Rfc2898DeriveBytes rfcKey = new Rfc2898DeriveBytes(passphrase, saltArray);
aes.Key = rfcKey.GetBytes(aes.KeySize / 8);
aes.IV = rfcKey.GetBytes(aes.BlockSize / 8);
// Encrypt the string to an array of bytes.
encrypted = EncryptStringToBytes_Aes(original, aes.Key, aes.IV);
// Decrypt the bytes to a string.
string roundtrip = DecryptStringFromBytes_Aes(encrypted, aes.Key, aes.IV);
return Convert.ToBase64String(encrypted);
}
and it works (DecryptStringFromBytes_Aes returns the original string).
My question is how do I decrypt encrypted using JavaScript if I have the same passphrase on the client-side as well? I tried using CryptoJS to decrypt it but had no success. The data gets encrypted in a webservice and I tried passing it to JS as a byte array, string, tried encoding it with various encodings but no matter what I did, I couldn't get the original string. What am I doing wrong here and how can I make this work? Is it even doable like this? Could the saltArray encoding or even the usage of the custom passphrase be the cause of my problems?
Here is for example one of my JS tries (using base64 encoding):
var decoded = CryptoJS.enc.Base64.parse(encrypted);
var decrypted = CryptoJS.AES.decrypt(decoded, "somepassphrase");
(edit: I meant to implement random salt later, once I got everything else wokring since it is easier to track what is going on that way)

try using Stanford Javascript Crypto Library.
Link:http://crypto.stanford.edu/sjcl/