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How to decrypt RSA encrypted string from JavaScript in C#?

I have an asymmetric RSA key pair stored in two separate files. I want to generate a new symmetric key and encrypt it with public RSA key in my postbuild.js GULP script, so the user cannot access it. Then I want to send it to the C# server, where it would be decrypted and used.
I use the following JavaScript code in Node.js for encryption:
const generateAndEncryptKey = () => {
const symmetricKey = crypto.randomBytes(32);
const publicKey = fs.readFileSync("pubkey.pem", "utf8");
const encryptedSymmetricKey = crypto.publicEncrypt({
key: publicKey,
padding: crypto.constants.RSA_PKCS1_OAEP_PADDING,
oaepHash: "sha256",
}, Buffer.from(symmetricKey)).toString("base64");
return encryptedSymmetricKey;
}
The above code somehow works and generates a base64 string that I later send to the server. I'm not sure if this is the correct way to do this.
But I'm unable to find a way to decrypt this string in C#. I tried to use the BouncyCastle library and the following code:
public string DecryptKey(string encryptedKey) {
var privateKey = #"-----BEGIN RSA PRIVATE KEY-----
...shortened...
-----END RSA PRIVATE KEY-----";
var bytesToDecrypt = Convert.FromBase64String(encryptedKey);
var decryptEngine = new Pkcs1Encoding(new RsaEngine());
using (var txtreader = new StringReader(privateKey)) {
AsymmetricCipherKeyPair keyPair = (AsymmetricCipherKeyPair)new PemReader(txtreader).ReadObject();
decryptEngine.Init(false, keyPair.Private);
}
var decrypted = Encoding.UTF8.GetString(decryptEngine.ProcessBlock(bytesToDecrypt, 0, bytesToDecrypt.Length));
return decrypted;
}
But the ProcessBlock method always throws an InvalidCipherTextException "unknown block type".
Can someone help me to find out what am I doing wrong or point me to another better way of achieving this?

Decryption with the C# code fails because in the NodeJS code OAEP/SHA256 is used as padding and in the C# code PKCS#1 v1.5 padding. For decryption to work, both paddings must be identical. The padding in the C# code can be adapted to that of the NodeJS code as follows:
var decryptEngine = new OaepEncoding(new RsaEngine(), new Sha256Digest());
Also, the decrypted key must not be UTF-8 decoded as this corrupts the data. Either it is returned as byte[], or if conversion to a string is desired, a suitable binary-to-text encoding such as Base64 or hex must be used.
With these changes decryption works in the C# code.

Decryption on java side

I found core library and Now I can encrypt and decrypt on Jsp
var encryptedpassword=CryptoJS.AES.encrypt(password,'abcd');
var ciphertext = encryptedpassword.ciphertext.toString(CryptoJS.enc.Base64);
console.log(ciphertext);
and decrypted using following
var decryptedpassword=CryptoJS.AES.decrypt(encryptedpassword,'abcd');
var plaintext = decryptedpassword.toString(CryptoJS.enc.Utf8);
console.log(plaintext);
My problem now is I want to decrypt the encrypted password on java side can some one tell me how can I do it?

RSA encrypt using jsencrypt and decrypt using bouncy castle?

Right I've a small problem. I'm using a Javascript library (jsencrypt) to encrypt a message in a browser. This message is then sent to the backend where it is decrypted using a Java library (bouncycastle). My problem is although I can encrypt and decrypt messages using both libraries they don't seem to want to work together. So when I encrypt my message in a browser and send it to the backend I end up getting garbled gibberish. Does anyone have any idea what's going on here?
JSENCRYPT
var text = "This is another msg!";
var pubkey = "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAwyTZf5gRWJdEevtK7sJSz14lhs1Jw7+aFhGtr4cbDGxdiXH8J+BwuYmBc6QFMhRw7AeYcgkx9zPb3SICzr+oK17RMA6T66dH+GPXp75LFUmfONfk2JdSeO80mMODGctSuefWDvoQ24Cq0Bz+ysrhP7hRqvJso5a0GMNPwt8ErtWfz4HZjSsaaZ7gXga2h5dq1OTcGNfevkDN9CJtFW/0Wwb/F6cnXngVHE41rsN4POUB3IWcX2CrCGxSraa+xsT/P7AJ8HRJ4wcjl9G2K/rlHJ8ZXZKlIuWwEzx0/F0IjE+S93tLpDgt6YJxjWqYqjL2uuJAGmEU323+PWA3jFTC+QIDAQAB";
var encrypt = new JSEncrypt();
encrypt.setPublicKey(pubkey);
var ciphertext = encrypt.encrypt(text);
console.log("ciphertext : " + ciphertext);
var decrypt = new JSEncrypt();
decrypt.setPrivateKey($("#privkey").val());
var plaintext = decrypt.decrypt(ciphertext);
console.log("plaintext : " + plaintext);
BOUNCYCASTLE
String cipherText = "jQ/I+oyyIfG5ARIHZsa6MfxwHciCt+3p6l+bLh4NPinq2s8eDjbO9O8abhVt2xuBQQcPAIaqbiP3Y3vRFYLOD2O+inKWiL1SpSBxvUb0XlWMgLmOqWUL6w6sL2iEla3i5EbdlrkK0uLA7QOUc6/fGVyLVe8VL7Vv4BGlo/cxR2FN74HK4MtLFRNaLKejwD6WbCNQoz4sIMA/Ez8GRSVEMyeYVZoWELShvyIRCqVADboAeuEP5l+oFlzgQfW6HFdpPnX+9TnHrbezdWhXiuJiD1Mq4VTicsya50MNcXJuPDV7NINYZs72UCS8NTYvfVkFc2lO7EUlDvvJ7Ns4wWuuWQ==";
PemReader pemReader = new PemReader(new InputStreamReader(new FileInputStream("priv.pem")));
PemObject pemObject = null;
try
{
pemObject = pemReader.readPemObject();
} finally {
pemReader.close();
}
PrivateKey privateKey = EncryptionUtil.generatePrivateKey(pemObject.getContent());
byte[] plainText = EncryptionUtil.asymDecrypt(privateKey, cipherText.getBytes());
System.out.println(new String(plainText));

#EbbeM.Pedersen
You are properly getting different default padding modes. Keywords
like RSA-OAEP padding & PKCS#1 padding comes to mind.
This was indeed the issue. I changed the default padding in bouncycastle to PKCS#1 and it all works now.
Thanks a million.

Different encryption in Crypto.js and .NET Cryptography using AES

I am trying to encrypt a message from client and decrypt it on the server. I put the AES key and iv in users cookies.
The problem is that the encrypted string from Crypto.js is G0eNQap/h6u+7566MTOH3w==, and the encrypted string from .NET is F7RemlJeNBhcaZ/FjCK4xw==. It has the same length, but not the same value.
I gues I am doing something wrong with encoding. Could you point out the mistake? Thanks in advance.
Crypto.js
var communicationKey = CryptoJS.enc.Base64.parse(getCookie("SessionKey"));
var communicationIV = CryptoJS.enc.Base64.parse(getCookie("IV"));
var encrypted = CryptoJS.AES.encrypt("Message", communicationKey, {
iv: communicationIV,
mode: CryptoJS.mode.CFB
});
console.log("Result: " + CryptoJS.enc.Base64.stringify(encrypted.ciphertext));
.NET:
string key = context.Cookies["SessionKey"].Value;
newUser.UserKey = Convert.FromBase64String(key);
string iv = context.Cookies["IV"].Value;
newUser.InitializationVector = Convert.FromBase64String(iv);
byte[] encryptedMessage = EncryptStringToBytes_Aes("Message", source.UserKey, source.InitializationVector);

In your js code you are using CryptoJS.mode.CFB.
If your EncryptStringToBytes_Aes is exact copy of MSDN sample - then it uses CBC AES encryption mode (it is default for AESManaged).
So you have to change either js or C# code for both of them use the same encryption mode.

Decrypt - Encrypt crypto-js

I am trying to get crypto-js library to encrypt/decrypt a simple message, please see the following jsfiddle (http://jsfiddle.net/6gunq2nx/)
<script>
var encrypted = CryptoJS.AES.encrypt("this is some test", "770A8A65DA156D24EE2A093277530142");
var decrypted = CryptoJS.AES.decrypt(encrypted, "770A8A65DA156D24EE2A093277530142");
alert(decrypted);
</script>
The problem is that, it is not decrypting the message properly, I have tried AES and DES but both do not work, what im I doing wrong? please see below screenshot

It's almost correct. The string you get is a hexadecimal representation of your original string. Try to convert it like this:
var decrypted = CryptoJS.AES.decrypt(encrypted, "770A8A65DA156D24EE2A093277530142").toString(CryptoJS.enc.Utf8);
forked jsfiddle: http://jsfiddle.net/1qgzk9j8/

try this :-
// Replace this with user input (only user should know the passphrase which can be used to decrypt the message)
var passphrase = '770A8A65DA156D24EE2A093277530142';
// Some content that we want to crypt
var content = 'this is some test';
// Use CryptoJS.AES to encrypt content using AES (Advanced Encryption Standard)
var encryptedContent = CryptoJS.AES.encrypt(content, passphrase);
// Use CryptoJS.AES also to decrypt content
var decryptedContent = CryptoJS.AES.decrypt(encryptedContent, passphrase).toString(CryptoJS.enc.Utf8);
alert(encryptedContent);
alert(decryptedContent);
Demo