How to create encrypted JWT in C# using RS256 with RSA private key

I am using the jose-jwt library and want to create a signed JWT in C# using the RS256 algorithm for encryption. I have no experience with cryptography, so please excuse my ignorance. I see the following example in the docs:

var payload = new Dictionary<string, object>()
{
    { "sub", "mr.x@contoso.com" },
    { "exp", 1300819380 }
};

var privateKey=new X509Certificate2("my-key.p12", "password", X509KeyStorageFlags.Exportable | X509KeyStorageFlags.MachineKeySet).PrivateKey as RSACryptoServiceProvider;

string token=Jose.JWT.Encode(payload, privateKey, JwsAlgorithm.RS256);

which shows the use of a p12 file, but how do I use an RSA key file of the form below? I am looking at the docs for X509Certificate2, but I see no option for RSA private keys. It appears to only accept PKCS7, which I understand to be public keys.

Finally, what is the difference between the two options listed in the docs, and how do I choose between the two?

-------------------------- OPTION 1 --------------------------

RS-* and PS-* family

CLR:

RS256, RS384, RS512 and PS256, PS384, PS512 signatures require RSACryptoServiceProvider (usually private) key of corresponding length. CSP need to be forced to use Microsoft Enhanced RSA and AES Cryptographic Provider. Which usually can be done be re-importing RSAParameters. See http://clrsecurity.codeplex.com/discussions/243156 for details.

-------------------------- OPTION 2 --------------------------

CORECLR: RS256, RS384, RS512 signatures require RSA (usually private) key of corresponding length.

I know this post is old, but it took me forever to figure this out, so I thought I would share.

To test I created RSA keys using OpenSSL:

openssl genrsa -out privateKey.pem 512
openssl rsa -in privateKey.pem -pubout -out publicKey.pem

You will need the following 2 nuget packages:

Test Code

public static void Test()
{
        string publicKey = File.ReadAllText(@"W:\Dev\Temp\rsa_keys\publicKey.pem");
        string privateKey = File.ReadAllText(@"W:\Dev\Temp\rsa_keys\privateKey.pem");

        var claims = new List<Claim>();
        claims.Add(new Claim("claim1", "value1"));
        claims.Add(new Claim("claim2", "value2"));
        claims.Add(new Claim("claim3", "value3"));

        var token = CreateToken(claims, privateKey);
        var payload = DecodeToken(token, publicKey);
    }

Create Token

    public static string CreateToken(List<Claim> claims, string privateRsaKey)
    {
        RSAParameters rsaParams;
        using (var tr = new StringReader(privateRsaKey))
        {
            var pemReader = new PemReader(tr);
            var keyPair = pemReader.ReadObject() as AsymmetricCipherKeyPair;
            if (keyPair == null)
            {
                throw new Exception("Could not read RSA private key");
            } 
            var privateRsaParams = keyPair.Private as RsaPrivateCrtKeyParameters;
            rsaParams = DotNetUtilities.ToRSAParameters(privateRsaParams);
        }
        using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
        {
            rsa.ImportParameters(rsaParams);
            Dictionary<string, object> payload = claims.ToDictionary(k => k.Type, v => (object)v.Value);
            return Jose.JWT.Encode(payload, rsa, Jose.JwsAlgorithm.RS256);
        }
    }

Decode Token

    public static string DecodeToken(string token, string publicRsaKey)
    {
        RSAParameters rsaParams;

        using (var tr = new StringReader(publicRsaKey))
        {
            var pemReader = new PemReader(tr);
            var publicKeyParams = pemReader.ReadObject() as RsaKeyParameters;
            if (publicKeyParams == null)
            {
                throw new Exception("Could not read RSA public key");
            }
            rsaParams = DotNetUtilities.ToRSAParameters(publicKeyParams);
        }
        using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
        {
            rsa.ImportParameters(rsaParams);
            // This will throw if the signature is invalid
            return Jose.JWT.Decode(token, rsa, Jose.JwsAlgorithm.RS256);  
        }
    }

I found https://jwt.io/ a great resource to test your tokens

Enrico

If you want to use a certificate, you can retrieve it by it's thumbprint using this method

private X509Certificate2 GetByThumbprint(string Thumbprint)
{
    var localStore = new X509Store(StoreName.My, StoreLocation.LocalMachine);
    localStore.Open(OpenFlags.ReadOnly);
    return localStore.Certificates//.Find(X509FindType.FindByKeyUsage, X509KeyUsageFlags.DigitalSignature, false)
        .Find(X509FindType.FindByThumbprint, Thumbprint, false)
        .OfType<X509Certificate2>().First();
}

and then:

private JwtSecurityToken GenerateJWT()
{
    var securityKey = new Microsoft.IdentityModel.Tokens.X509SecurityKey(GetByThumbprint("YOUR-CERT-THUMBPRINT-HERE"));

    var credentials = new Microsoft.IdentityModel.Tokens.SigningCredentials(securityKey, "RS256");

    var JWTHeader = new JwtHeader(credentials);

    var payload = new JwtPayload
    {
        { "iss", "Issuer-here"},
        { "exp", (Int32)(DateTime.UtcNow.AddHours(1).Subtract(new DateTime(1970, 1, 1))).TotalSeconds},
        { "iat", (Int32)(DateTime.UtcNow.Subtract(new DateTime(1970, 1, 1))).TotalSeconds}
    };

    var token = new JwtSecurityToken(JWTHeader, payload);
    return token;
}

The GetRSAPrivateKey is only available in .NET 4.6. See the URL below.

https://msdn.microsoft.com/en-us/library/system.security.cryptography.x509certificates.rsacertificateextensions.getrsaprivatekey(v=vs.110).aspx

If you use a public certificate and .NET 4.6,for decoding you can use:

string token = "eyJhbGciOiJSUzI1NiIsInR....";
string certificate = "MIICnzCCAYcCBgFd2yEPx....";
var publicKey = new X509Certificate2(Convert.FromBase64String(certificate )).GetRSAPublicKey();
string decoded = JWT.Decode(token, publicKey, JwsAlgorithm.RS256);

RS256 is a Signature Algorithm not an Encryption Algorithm
Encryption is done with the public key

Here is the code to create an encrypted JWT:

var cert = new X509Certificate2(".\\key.cer");
var rsa = (RSACryptoServiceProvider) cert.PublicKey.Key;

var payload = new Dictionary<string, object>()
{
  {"sub", "mr.x@contoso.com"},
  {"exp", 1300819380}
};

var encryptedToken =
  JWT.Encode(
    payload,
    rsa,
    JweAlgorithm.RSA_OAEP,
    JweEncryption.A256CBC_HS512,
    null);

The key to this question is using JWT and Bouncy castle libraries for encoding the token and signing it respectively.

JWT for encoding and decoding JWT tokens
Bouncy Castle supports encryption and decryption, especially RS256 get it here

First, you need to transform the private key to the form of RSA parameters. Then you need to pass the RSA parameters to the RSA algorithm as the private key. Lastly, you use the JWT library to encode and sign the token.

    public string GenerateJWTToken(string rsaPrivateKey)
    {
        var rsaParams = GetRsaParameters(rsaPrivateKey);
        var encoder = GetRS256JWTEncoder(rsaParams);

        // create the payload according to your need
        var payload = new Dictionary<string, object>
        {
            { "iss", ""},
            { "sub", "" },
            // and other key-values 
        };

        // add headers. 'alg' and 'typ' key-values are added automatically.
        var header = new Dictionary<string, object>
        {
            { "{header_key}", "{your_private_key_id}" },
        };

        var token = encoder.Encode(header,payload, new byte[0]);

        return token;
    }

    private static IJwtEncoder GetRS256JWTEncoder(RSAParameters rsaParams)
    {
        var csp = new RSACryptoServiceProvider();
        csp.ImportParameters(rsaParams);

        var algorithm = new RS256Algorithm(csp, csp);
        var serializer = new JsonNetSerializer();
        var urlEncoder = new JwtBase64UrlEncoder();
        var encoder = new JwtEncoder(algorithm, serializer, urlEncoder);

        return encoder;
    }

    private static RSAParameters GetRsaParameters(string rsaPrivateKey)
    {
        var byteArray = Encoding.ASCII.GetBytes(rsaPrivateKey);
        using (var ms = new MemoryStream(byteArray))
        {
            using (var sr = new StreamReader(ms))
            {
                // use Bouncy Castle to convert the private key to RSA parameters
                var pemReader = new PemReader(sr);
                var keyPair = pemReader.ReadObject() as AsymmetricCipherKeyPair;
                return DotNetUtilities.ToRSAParameters(keyPair.Private as RsaPrivateCrtKeyParameters);
            }
        }
    }

ps: the RSA private key should have the following format:

-----BEGIN RSA PRIVATE KEY-----

{base64 formatted value}

-----END RSA PRIVATE KEY-----

来源：https://stackoverflow.com/questions/38794670/how-to-create-encrypted-jwt-in-c-sharp-using-rs256-with-rsa-private-key

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