How to Encryption JWT Payload with Public Key RSA_OAEP_256

How to Encryption JWT Payload with Public Key RSA_OAEP_256 - c#

I'm using "BouncyCastle.NetCore" and "jose-jwt" libraries to sign and encrypt a web token. I'm able to sign with my private key by below code. but the requirements is to also perform OpenID JWT Encryption In order to encrypt the JWT payload, we need to do that using provided public key string (base64 decoded with X509 key spec).
the encode needed to use RSA algorithm and JWE header should include header name “alg" with the value: RSA_OAEP_256.
Below code is sign only with private key but not sure how to complete the encode??
class Program
{
string publicKeyString = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCqGKukO1De7zhZj6+H0qtjTkVxwTCpvKe4eCZ0FPqri0cb2JZfXJ/DgYSF6vUpwmJG8wVQZKjeGcjDOL5UlsuusFncCzWBQ7RKNUSesmQRMSGkVb1/3j+skZ6UtW+5u09lHNsj6tQ51s1SPrCBkedbNf0Tp0GbMJDyR4e9T04ZZwIDAQAB";
public static async Task Main(string[] args)
{
var payload = new System.Collections.Generic.Dictionary<string, object>()
{
{ "sub", "Testmr.x#contoso.com" },
{ "iss", "https://www.YourBrand.com" },
{ "exp", 1300819380 },
{ "iat", 1446111752 },
{ "preferred_username", "JohnDoe2" },
{ "phone_number", "+2-10-344-3765333" }
};
var token = CreateToken(payload);
Console.WriteLine($"token={token}");
}
public static string CreateToken(object payload)
{
string jwt = string.Empty;
var fileStream = System.IO.File.OpenText("C:\\temp\\my_private_key.pem");
var pemReader = new Org.BouncyCastle.OpenSsl.PemReader(fileStream, new MyPasswordFinder());
var keyPair = (Org.BouncyCastle.Crypto.AsymmetricKeyParameter)pemReader.ReadObject();
RSAParameters rsaParams = DotNetUtilities.ToRSAParameters((RsaPrivateCrtKeyParameters)keyPair);
using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
{
rsa.ImportParameters(rsaParams);
jwt = JWT.Encode(payload, rsa, JwsAlgorithm.RS256);//,options: new JwtOptions { EncodePayload = true }
}
return jwt;
}
}

The only difference EncodePayload seems to make is how payload ends up being written out to JWT body. It is true by default and does not affect payload encryption (see source code):
return jwtOptions.EncodePayload
? Compact.Serialize(headerBytes, payloadBytes, signature)
: Compact.Serialize(headerBytes, Encoding.UTF8.GetString(payloadBytes), signature);
What you probably want is to specify JweAlgorithm and correct JweEncryption (note, it's a different overload to the same function:
jwt = JWT.Encode(payload, rsa, JweAlgorithm.RSA_OAEP_256, JweEncryption.A256GCM);

Related

Signing data with RSA512 v2 [duplicate]

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.
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
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:
https://github.com/dvsekhvalnov/jose-jwt
http://www.bouncycastle.org/csharp/
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

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-----

I used http://travistidwell.com/jsencrypt/demo/
to create 2048 bit keys
Using .NET 6:
string CreateRsaToken(string someClaimValue)
{
var rsaPrivateKey = #"-----BEGIN RSA PRIVATE KEY-----
MIIEogIBA...";
using var rsa = RSA.Create();
rsa.ImportFromPem(rsaPrivateKey);
var signingCredentials = new SigningCredentials(new RsaSecurityKey(rsa), SecurityAlgorithms.RsaSha256)
{
CryptoProviderFactory = new CryptoProviderFactory { CacheSignatureProviders = false }
};
var now = DateTime.Now;
var jwt = new JwtSecurityToken(
audience: "all",
issuer: "TheBitCoinKing",
claims: new[] {
new Claim("SomeClaim", someClaimValue),
},
notBefore: now,
expires: now.AddMinutes(1),
signingCredentials: signingCredentials
);
return new JwtSecurityTokenHandler().WriteToken(jwt);
}
packages:
Microsoft.IdentityModel.Tokens
System.IdentityModel.Tokens.Jwt

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;
}

Using BouncyCastle and Jose nuget package, the following code works for me.
public static string CreateToken(Dictionary<string, object> payload)
{
string jwt = string.Empty;
RsaPrivateCrtKeyParameters keyPair;
var cert = ConfigurationManager.AppSettings["cert"];
/// cert begins -----BEGIN PRIVATE KEY----- and ends with -END PRIVATE KEY-----";
using (var sr = new StringReader(cert))
{
PemReader pr = new PemReader(sr);
keyPair = (RsaPrivateCrtKeyParameters)pr.ReadObject();
}
RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyPair);
using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
{
rsa.ImportParameters(rsaParams);
jwt = Jose.JWT.Encode(payload, rsa, Jose.JwsAlgorithm.RS256);
}
return jwt;
}

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

Posting the code to create RS256 JWT token for GCP OAuth Token API call, using the Service Account JSON Key-:
using JWT;
using JWT.Algorithms;
using JWT.Serializers;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Security;
using System;
using System.Collections.Generic;
using System.Security.Cryptography;
namespace GCP
{
class JWTTokenGenerationForGCPOAuthTokenAPI
{
public static string GenerateJWTToken()
{
var rsaParams = ReadAsymmetricKeyParameter();
var encoder = GetRS256JWTEncoder(rsaParams);
var iat = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
var exp = DateTimeOffset.UtcNow.AddMinutes(60).ToUnixTimeSeconds();
// create the payload according to your need
// iss is the Service Account Email ID
var payload = new Dictionary<string, object>
{
{ "iss", "<service-account>#<project-id>.iam.gserviceaccount.com"},
{ "scope", "https://www.googleapis.com/auth/cloud-platform" },
{ "aud", "https://oauth2.googleapis.com/token" },
{ "exp", exp},
{ "iat", iat}
};
//Final token
var token = encoder.Encode(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;
}
public static RSAParameters ReadAsymmetricKeyParameter()
{
\\ This key is fetched from the GCP Service Account JSON File.
\\"private_key": "-----BEGIN PRIVATE KEY-----\n<long-code>-----END PRIVATE KEY-----\n",
\\ pick <long-code> from above. Replace all \n with actual new line like shown below.
string pkey = #"MIIEvAIBADANBgkqhkiG9w0BAQEFAASCBKYwggSiAgEAAoIBAQDSoGKK/Dzb8MBy
################################################################
################################################################
################################################################
################################################################
twySMqKKWnIC/zZljrvp4w==";
RsaPrivateCrtKeyParameters rsaPrivateCrtKeyParameters1;
var keyBytes = Convert.FromBase64String(pkey);
var asymmetricKeyParameter = PrivateKeyFactory.CreateKey(keyBytes);
rsaPrivateCrtKeyParameters1 = (RsaPrivateCrtKeyParameters)asymmetricKeyParameter;
RSAParameters r = DotNetUtilities.ToRSAParameters(rsaPrivateCrtKeyParameters1);
return r;
}
}
}
Code Done in : .NET Framework 4.6.1
Nuget Packages :
Bounty Castle - Install-Package BouncyCastle -Version 1.8.6.1

I thought I would add my findings as I had to do this last night. The examples in this page really helped but they didn't work straightaway.
In my specific case, I was trying to generate a JWT token for DocuSign, for some other reason I can't use their SDK and generating the JWT token manually was the right approach for my use case.
var privateKeybyteArray = Encoding.ASCII.GetBytes(#"-----BEGIN RSA PRIVATE KEY-----
xxxxxxxxxxxxxxxxxx
-----END RSA PRIVATE KEY-----");
var payload = new Dictionary<string, object>
{
{ "iss", "3a31fd58-xxxx-xxxx-xxxx-17639ade3c1b" },
{ "sub", "40a3a606-xxxx-xxxx-xxxx-762c6e7dadb6" },
{ "aud", "account-d.docusign.com" },
{ "iat", DateTime.UtcNow.Subtract(new DateTime(1970, 1, 1)).TotalSeconds },
{ "exp", DateTime.UtcNow.AddHours(1).Subtract(new DateTime(1970, 1, 1)).TotalSeconds },
{ "scope", "signature" }
};
var rsaPrivateKey = new RSAParameters();
using (var ms = new MemoryStream(privateKeybyteArray))
{
using (var sr = new StreamReader(ms))
{
var pemReader = new PemReader(sr);
var keyPair = pemReader.ReadObject() as AsymmetricCipherKeyPair;
rsaPrivateKey = DotNetUtilities.ToRSAParameters(keyPair.Private as RsaPrivateCrtKeyParameters);
}
}
var csprivate = new RSACryptoServiceProvider();
csprivate.ImportParameters(rsaPrivateKey);
var algorithm = new RS256Algorithm(csprivate, csprivate);
var serializer = new JsonNetSerializer();
var urlEncoder = new JwtBase64UrlEncoder();
var encoder = new JwtEncoder(algorithm, serializer, urlEncoder);
var token = encoder.Encode(payload, privateKeybyteArray);
I used the JWT-dotnet package. I found the website jsonwebtoken.io really good as it generates the .NET code needed for generating the token, it didn't quite work but it helped for figuring out what I was doing wrong

NET 5.0 or later has a method called "ImportFromPem", so you can read private-key in PEM format as it is.
void GetToken(System.IO.FileInfo privateKey, string service_account, string client_id)
{
using (var rsa = System.Security.Cryptography.RSA.Create())
{
rsa.ImportFromPem(System.IO.File.ReadAllText(privateKey.FullName));
var descriptor = new Microsoft.IdentityModel.Tokens.SecurityTokenDescriptor
{
Issuer = client_id,
Claims = new System.Collections.Generic.Dictionary<string, object>() { ["sub"] = service_account },
SigningCredentials = new Microsoft.IdentityModel.Tokens.SigningCredentials(new Microsoft.IdentityModel.Tokens.RsaSecurityKey(rsa), SecurityAlgorithms.RsaSha256),
IssuedAt = System.DateTime.UtcNow,
Expires = System.DateTime.UtcNow.AddMinutes(60),
};
var handler = new System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler();
string token = handler.WriteToken(handler.CreateJwtSecurityToken(descriptor));
}
}
Nuget: 「System.IdentityModel.Tokens.Jwt」
And, maybe error: cannot access a disposed object. object name 'rsa' -> Ref
var signingCredentials = new SigningCredentials(rsaSecurityKey, SecurityAlgorithms.RsaSha256)
{
CryptoProviderFactory = new CryptoProviderFactory { CacheSignatureProviders = false }
};

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);

How to generate JWT token signed with RS256 algorithm in C#

I have a RSA Private key with me and I have to generate a JWT token using RS256 algorithm.
I started with the below code which was working for "HmacSha256" algorithm
but when i change it to RS256 it throws errors like " IDX10634: Unable to create the SignatureProvider.Algorithm: 'System.String',SecurityKey:'Microsoft.IdentityModel.Tokens.SymmetricSecurityKey'"
After that I modified the code with RSACryptoServiceProvider() class. But i didnt get a solution.
Please anyone can help with a sample code using RSACryptoServiceProvider class with a private key.
public static string CreateToken()//Dictionary<string, object> payload
{
string key = GetConfiguration["privateKey"].Tostring();
var securityKey =
new Microsoft.IdentityModel.Tokens.SymmetricSecurityKey(
Encoding.UTF8.GetBytes(key));
var credentials =
new Microsoft.IdentityModel.Tokens.SigningCredentials(securityKey, "RS256");
var header = new JwtHeader(credentials);
JwtPayload payload = new JwtPayload();
payload.AddClaim(
new System.Security.Claims.Claim(
"context", "{'user': { 'name': 'username', 'email': 'email' }}",
JsonClaimValueTypes.Json));
payload.AddClaim(new System.Security.Claims.Claim("iss", #"app-key"));
payload.AddClaim(new System.Security.Claims.Claim("aud", "meet.jitsi.com"));
payload.AddClaim(new System.Security.Claims.Claim("sub", "meet.jitsi.com"));
payload.AddClaim(new System.Security.Claims.Claim("room", "TestRoom"));
var secToken = new JwtSecurityToken(header, payload);
var handler = new JwtSecurityTokenHandler();
var tokenString = handler.WriteToken(secToken);
return tokenString;
}

JWT token generated with jose-jwt and jwt.io

I'm trying to generate JWT token in .NET. At first, I tried to use "System.IdentityModel.Tokens.Jwt" but it was causing an issue during the validation of the token, so I switched to "jose-jwt". Even though I can create and validate a token with this piece of code:
private byte[] GetBytes(string str)
{
byte[] bytes = new byte[str.Length * sizeof(char)];
Buffer.BlockCopy(str.ToCharArray(), 0, bytes, 0, bytes.Length);
return bytes;
}
public string Login(LoginInformation credential)
{
var payload = new Dictionary<string, object>()
{
{ "sub", "mr.x#contoso.com" },
{ "exp", 1300819380 }
};
var secretKey = GetBytes("myawesomekey");
string token = JWT.Encode(payload, secretKey, JwsAlgorithm.HS256);
string json = JWT.Decode(token, secretKey);
return json;
}
I have an issue when I try to test the generated token with the site "https://jwt.io/". Indeed, I copy/paste the generated token, I enter "myawesomekey" as the key but it keeps telling me "invalid signature".
I could just ignore that (as the decoding in my C# code works), but I'm quite curious and I'd like to know how come the decoding via the site fails. The only idea I have is that, in the C# code, I have to pass the key as a byte array, so maybe it's not valid to just pass "myawesomekey" to the site.

You're getting the bytes incorrectly for the key:
var payload = new Dictionary<string, object>()
{
{ "sub", "mr.x#contoso.com" },
{ "exp", 1300819380 }
};
var secretKey = Encoding.UTF8.GetBytes("myawesomekey");
string token = JWT.Encode(payload, secretKey, JwsAlgorithm.HS256);
return token;
Works fine. This is probably also the cause of your problem with System.IdentityModel.Tokens.Jwt.

How to sign a JWT 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.
-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
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:
https://github.com/dvsekhvalnov/jose-jwt
http://www.bouncycastle.org/csharp/
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

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-----

I used http://travistidwell.com/jsencrypt/demo/
to create 2048 bit keys
Using .NET 6:
string CreateRsaToken(string someClaimValue)
{
var rsaPrivateKey = #"-----BEGIN RSA PRIVATE KEY-----
MIIEogIBA...";
using var rsa = RSA.Create();
rsa.ImportFromPem(rsaPrivateKey);
var signingCredentials = new SigningCredentials(new RsaSecurityKey(rsa), SecurityAlgorithms.RsaSha256)
{
CryptoProviderFactory = new CryptoProviderFactory { CacheSignatureProviders = false }
};
var now = DateTime.Now;
var jwt = new JwtSecurityToken(
audience: "all",
issuer: "TheBitCoinKing",
claims: new[] {
new Claim("SomeClaim", someClaimValue),
},
notBefore: now,
expires: now.AddMinutes(1),
signingCredentials: signingCredentials
);
return new JwtSecurityTokenHandler().WriteToken(jwt);
}
packages:
Microsoft.IdentityModel.Tokens
System.IdentityModel.Tokens.Jwt

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;
}

Using BouncyCastle and Jose nuget package, the following code works for me.
public static string CreateToken(Dictionary<string, object> payload)
{
string jwt = string.Empty;
RsaPrivateCrtKeyParameters keyPair;
var cert = ConfigurationManager.AppSettings["cert"];
/// cert begins -----BEGIN PRIVATE KEY----- and ends with -END PRIVATE KEY-----";
using (var sr = new StringReader(cert))
{
PemReader pr = new PemReader(sr);
keyPair = (RsaPrivateCrtKeyParameters)pr.ReadObject();
}
RSAParameters rsaParams = DotNetUtilities.ToRSAParameters(keyPair);
using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
{
rsa.ImportParameters(rsaParams);
jwt = Jose.JWT.Encode(payload, rsa, Jose.JwsAlgorithm.RS256);
}
return jwt;
}

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

Posting the code to create RS256 JWT token for GCP OAuth Token API call, using the Service Account JSON Key-:
using JWT;
using JWT.Algorithms;
using JWT.Serializers;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Security;
using System;
using System.Collections.Generic;
using System.Security.Cryptography;
namespace GCP
{
class JWTTokenGenerationForGCPOAuthTokenAPI
{
public static string GenerateJWTToken()
{
var rsaParams = ReadAsymmetricKeyParameter();
var encoder = GetRS256JWTEncoder(rsaParams);
var iat = DateTimeOffset.UtcNow.ToUnixTimeSeconds();
var exp = DateTimeOffset.UtcNow.AddMinutes(60).ToUnixTimeSeconds();
// create the payload according to your need
// iss is the Service Account Email ID
var payload = new Dictionary<string, object>
{
{ "iss", "<service-account>#<project-id>.iam.gserviceaccount.com"},
{ "scope", "https://www.googleapis.com/auth/cloud-platform" },
{ "aud", "https://oauth2.googleapis.com/token" },
{ "exp", exp},
{ "iat", iat}
};
//Final token
var token = encoder.Encode(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;
}
public static RSAParameters ReadAsymmetricKeyParameter()
{
\\ This key is fetched from the GCP Service Account JSON File.
\\"private_key": "-----BEGIN PRIVATE KEY-----\n<long-code>-----END PRIVATE KEY-----\n",
\\ pick <long-code> from above. Replace all \n with actual new line like shown below.
string pkey = #"MIIEvAIBADANBgkqhkiG9w0BAQEFAASCBKYwggSiAgEAAoIBAQDSoGKK/Dzb8MBy
################################################################
################################################################
################################################################
################################################################
twySMqKKWnIC/zZljrvp4w==";
RsaPrivateCrtKeyParameters rsaPrivateCrtKeyParameters1;
var keyBytes = Convert.FromBase64String(pkey);
var asymmetricKeyParameter = PrivateKeyFactory.CreateKey(keyBytes);
rsaPrivateCrtKeyParameters1 = (RsaPrivateCrtKeyParameters)asymmetricKeyParameter;
RSAParameters r = DotNetUtilities.ToRSAParameters(rsaPrivateCrtKeyParameters1);
return r;
}
}
}
Code Done in : .NET Framework 4.6.1
Nuget Packages :
Bounty Castle - Install-Package BouncyCastle -Version 1.8.6.1

I thought I would add my findings as I had to do this last night. The examples in this page really helped but they didn't work straightaway.
In my specific case, I was trying to generate a JWT token for DocuSign, for some other reason I can't use their SDK and generating the JWT token manually was the right approach for my use case.
var privateKeybyteArray = Encoding.ASCII.GetBytes(#"-----BEGIN RSA PRIVATE KEY-----
xxxxxxxxxxxxxxxxxx
-----END RSA PRIVATE KEY-----");
var payload = new Dictionary<string, object>
{
{ "iss", "3a31fd58-xxxx-xxxx-xxxx-17639ade3c1b" },
{ "sub", "40a3a606-xxxx-xxxx-xxxx-762c6e7dadb6" },
{ "aud", "account-d.docusign.com" },
{ "iat", DateTime.UtcNow.Subtract(new DateTime(1970, 1, 1)).TotalSeconds },
{ "exp", DateTime.UtcNow.AddHours(1).Subtract(new DateTime(1970, 1, 1)).TotalSeconds },
{ "scope", "signature" }
};
var rsaPrivateKey = new RSAParameters();
using (var ms = new MemoryStream(privateKeybyteArray))
{
using (var sr = new StreamReader(ms))
{
var pemReader = new PemReader(sr);
var keyPair = pemReader.ReadObject() as AsymmetricCipherKeyPair;
rsaPrivateKey = DotNetUtilities.ToRSAParameters(keyPair.Private as RsaPrivateCrtKeyParameters);
}
}
var csprivate = new RSACryptoServiceProvider();
csprivate.ImportParameters(rsaPrivateKey);
var algorithm = new RS256Algorithm(csprivate, csprivate);
var serializer = new JsonNetSerializer();
var urlEncoder = new JwtBase64UrlEncoder();
var encoder = new JwtEncoder(algorithm, serializer, urlEncoder);
var token = encoder.Encode(payload, privateKeybyteArray);
I used the JWT-dotnet package. I found the website jsonwebtoken.io really good as it generates the .NET code needed for generating the token, it didn't quite work but it helped for figuring out what I was doing wrong

NET 5.0 or later has a method called "ImportFromPem", so you can read private-key in PEM format as it is.
void GetToken(System.IO.FileInfo privateKey, string service_account, string client_id)
{
using (var rsa = System.Security.Cryptography.RSA.Create())
{
rsa.ImportFromPem(System.IO.File.ReadAllText(privateKey.FullName));
var descriptor = new Microsoft.IdentityModel.Tokens.SecurityTokenDescriptor
{
Issuer = client_id,
Claims = new System.Collections.Generic.Dictionary<string, object>() { ["sub"] = service_account },
SigningCredentials = new Microsoft.IdentityModel.Tokens.SigningCredentials(new Microsoft.IdentityModel.Tokens.RsaSecurityKey(rsa), SecurityAlgorithms.RsaSha256),
IssuedAt = System.DateTime.UtcNow,
Expires = System.DateTime.UtcNow.AddMinutes(60),
};
var handler = new System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler();
string token = handler.WriteToken(handler.CreateJwtSecurityToken(descriptor));
}
}
Nuget: 「System.IdentityModel.Tokens.Jwt」
And, maybe error: cannot access a disposed object. object name 'rsa' -> Ref
var signingCredentials = new SigningCredentials(rsaSecurityKey, SecurityAlgorithms.RsaSha256)
{
CryptoProviderFactory = new CryptoProviderFactory { CacheSignatureProviders = false }
};

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);

Verifying JWT signed with the RS256 algorithm using public key in C#

Ok, I understand that the question I am asking may be pretty obvious, but unfortunately I lack the knowledge on this subject and this task seems to be quite tricky for me.
I have an id token (JWT) returned by OpenID Connect Provider. Here it is:
eyJraWQiOiIxZTlnZGs3IiwiYWxnIjoiUlMyNTYifQ.ewogImlzcyI6ICJodHRwOi8vc2VydmVyLmV4YW1wbGUuY29tIiwKICJzdWIiOiAiMjQ4Mjg5NzYxMDAxIiwKICJhdWQiOiAiczZCaGRSa3F0MyIsCiAibm9uY2UiOiAibi0wUzZfV3pBMk1qIiwKICJleHAiOiAxMzExMjgxOTcwLAogImlhdCI6IDEzMTEyODA5NzAsCiAiY19oYXNoIjogIkxEa3RLZG9RYWszUGswY25YeENsdEEiCn0.XW6uhdrkBgcGx6zVIrCiROpWURs-4goO1sKA4m9jhJIImiGg5muPUcNegx6sSv43c5DSn37sxCRrDZZm4ZPBKKgtYASMcE20SDgvYJdJS0cyuFw7Ijp_7WnIjcrl6B5cmoM6ylCvsLMwkoQAxVublMwH10oAxjzD6NEFsu9nipkszWhsPePf_rM4eMpkmCbTzume-fzZIi5VjdWGGEmzTg32h3jiex-r5WTHbj-u5HL7u_KP3rmbdYNzlzd1xWRYTUs4E8nOTgzAUwvwXkIQhOh5TPcSMBYy6X3E7-_gr9Ue6n4ND7hTFhtjYs3cjNKIA08qm5cpVYFMFMG6PkhzLQ
Its header and payload are decoded as this:
{
"kid":"1e9gdk7",
"alg":"RS256"
}.
{
"iss": "http://server.example.com",
"sub": "248289761001",
"aud": "s6BhdRkqt3",
"nonce": "n-0S6_WzA2Mj",
"exp": 1311281970,
"iat": 1311280970,
"c_hash": "LDktKdoQak3Pk0cnXxCltA"
}
From the OIDC provider's discovery, I've got the public key (JWK):
{
"kty":"RSA",
"kid":"1e9gdk7",
"n":"w7Zdfmece8iaB0kiTY8pCtiBtzbptJmP28nSWwtdjRu0f2GFpajvWE4VhfJAjEsOcwYzay7XGN0b-X84BfC8hmCTOj2b2eHT7NsZegFPKRUQzJ9wW8ipn_aDJWMGDuB1XyqT1E7DYqjUCEOD1b4FLpy_xPn6oV_TYOfQ9fZdbE5HGxJUzekuGcOKqOQ8M7wfYHhHHLxGpQVgL0apWuP2gDDOdTtpuld4D2LK1MZK99s9gaSjRHE8JDb1Z4IGhEcEyzkxswVdPndUWzfvWBBWXWxtSUvQGBRkuy1BHOa4sP6FKjWEeeF7gm7UMs2Nm2QUgNZw6xvEDGaLk4KASdIxRQ",
"e":"AQAB"
}
So, the question is how exactly in C# can I verify this JWT using the public key for the RS256 algorithm I've got? It would be awesome if there is a good tutorial describing this procedure explicitly. However, an example of how to do this using System.IdentityModel.Tokens.Jwt will also work fine.
UPDATE:
I understand, that I need to do something like the code below, but I have no idea where to get 'key' for calculating SHA256 hash.
string tokenStr = "eyJraWQiOiIxZTlnZGs3IiwiYWxnIjoiUlMyNTYifQ.ewogImlzcyI6ICJodHRwOi8vc2VydmVyLmV4YW1wbGUuY29tIiwKICJzdWIiOiAiMjQ4Mjg5NzYxMDAxIiwKICJhdWQiOiAiczZCaGRSa3F0MyIsCiAibm9uY2UiOiAibi0wUzZfV3pBMk1qIiwKICJleHAiOiAxMzExMjgxOTcwLAogImlhdCI6IDEzMTEyODA5NzAsCiAiY19oYXNoIjogIkxEa3RLZG9RYWszUGswY25YeENsdEEiCn0.XW6uhdrkBgcGx6zVIrCiROpWURs-4goO1sKA4m9jhJIImiGg5muPUcNegx6sSv43c5DSn37sxCRrDZZm4ZPBKKgtYASMcE20SDgvYJdJS0cyuFw7Ijp_7WnIjcrl6B5cmoM6ylCvsLMwkoQAxVublMwH10oAxjzD6NEFsu9nipkszWhsPePf_rM4eMpkmCbTzume-fzZIi5VjdWGGEmzTg32h3jiex-r5WTHbj-u5HL7u_KP3rmbdYNzlzd1xWRYTUs4E8nOTgzAUwvwXkIQhOh5TPcSMBYy6X3E7-_gr9Ue6n4ND7hTFhtjYs3cjNKIA08qm5cpVYFMFMG6PkhzLQ";
string[] tokenParts = tokenStr.Split('.');
RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
rsa.ImportParameters(
new RSAParameters() {
Modulus = FromBase64Url("w7Zdfmece8iaB0kiTY8pCtiBtzbptJmP28nSWwtdjRu0f2GFpajvWE4VhfJAjEsOcwYzay7XGN0b-X84BfC8hmCTOj2b2eHT7NsZegFPKRUQzJ9wW8ipn_aDJWMGDuB1XyqT1E7DYqjUCEOD1b4FLpy_xPn6oV_TYOfQ9fZdbE5HGxJUzekuGcOKqOQ8M7wfYHhHHLxGpQVgL0apWuP2gDDOdTtpuld4D2LK1MZK99s9gaSjRHE8JDb1Z4IGhEcEyzkxswVdPndUWzfvWBBWXWxtSUvQGBRkuy1BHOa4sP6FKjWEeeF7gm7UMs2Nm2QUgNZw6xvEDGaLk4KASdIxRQ"),
Exponent = FromBase64Url("AQAB")
});
HMACSHA256 sha = new HMACSHA256(key);
byte[] hash = sha.ComputeHash(Encoding.UTF8.GetBytes(tokenParts[0] + '.' + tokenParts[1]));
byte[] signature = rsa.Encrypt(hash, false);
string strSignature = Base64UrlEncode(signature);
if (String.Compare(strSignature, tokenParts[2], false) == 0)
return true;

Thanks to jwilleke, I have got a solution. To verify the RS256 signature of a JWT, it is needed to use the RSAPKCS1SignatureDeformatter class and its VerifySignature method.
Here is the exact code for my sample data:
string tokenStr = "eyJraWQiOiIxZTlnZGs3IiwiYWxnIjoiUlMyNTYifQ.ewogImlzcyI6ICJodHRwOi8vc2VydmVyLmV4YW1wbGUuY29tIiwKICJzdWIiOiAiMjQ4Mjg5NzYxMDAxIiwKICJhdWQiOiAiczZCaGRSa3F0MyIsCiAibm9uY2UiOiAibi0wUzZfV3pBMk1qIiwKICJleHAiOiAxMzExMjgxOTcwLAogImlhdCI6IDEzMTEyODA5NzAsCiAiY19oYXNoIjogIkxEa3RLZG9RYWszUGswY25YeENsdEEiCn0.XW6uhdrkBgcGx6zVIrCiROpWURs-4goO1sKA4m9jhJIImiGg5muPUcNegx6sSv43c5DSn37sxCRrDZZm4ZPBKKgtYASMcE20SDgvYJdJS0cyuFw7Ijp_7WnIjcrl6B5cmoM6ylCvsLMwkoQAxVublMwH10oAxjzD6NEFsu9nipkszWhsPePf_rM4eMpkmCbTzume-fzZIi5VjdWGGEmzTg32h3jiex-r5WTHbj-u5HL7u_KP3rmbdYNzlzd1xWRYTUs4E8nOTgzAUwvwXkIQhOh5TPcSMBYy6X3E7-_gr9Ue6n4ND7hTFhtjYs3cjNKIA08qm5cpVYFMFMG6PkhzLQ";
string[] tokenParts = tokenStr.Split('.');
RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
rsa.ImportParameters(
new RSAParameters() {
Modulus = FromBase64Url("w7Zdfmece8iaB0kiTY8pCtiBtzbptJmP28nSWwtdjRu0f2GFpajvWE4VhfJAjEsOcwYzay7XGN0b-X84BfC8hmCTOj2b2eHT7NsZegFPKRUQzJ9wW8ipn_aDJWMGDuB1XyqT1E7DYqjUCEOD1b4FLpy_xPn6oV_TYOfQ9fZdbE5HGxJUzekuGcOKqOQ8M7wfYHhHHLxGpQVgL0apWuP2gDDOdTtpuld4D2LK1MZK99s9gaSjRHE8JDb1Z4IGhEcEyzkxswVdPndUWzfvWBBWXWxtSUvQGBRkuy1BHOa4sP6FKjWEeeF7gm7UMs2Nm2QUgNZw6xvEDGaLk4KASdIxRQ"),
Exponent = FromBase64Url("AQAB")
});
SHA256 sha256 = SHA256.Create();
byte[] hash = sha256.ComputeHash(Encoding.UTF8.GetBytes(tokenParts[0] + '.' + tokenParts[1]));
RSAPKCS1SignatureDeformatter rsaDeformatter = new RSAPKCS1SignatureDeformatter(rsa);
rsaDeformatter.SetHashAlgorithm("SHA256");
if (rsaDeformatter.VerifySignature(hash, FromBase64Url(tokenParts[2])))
MessageBox.Show("Signature is verified");
//...
static byte[] FromBase64Url(string base64Url)
{
string padded = base64Url.Length % 4 == 0
? base64Url : base64Url + "====".Substring(base64Url.Length % 4);
string base64 = padded.Replace("_", "/")
.Replace("-", "+");
return Convert.FromBase64String(base64);
}

Here is an example using IdentityModel.Tokens.Jwt for validation:
string tokenStr = "eyJraWQiOiIxZTlnZGs3IiwiYWxnIjoiUlMyNTYifQ.ewogImlzcyI6ICJodHRwOi8vc2VydmVyLmV4YW1wbGUuY29tIiwKICJzdWIiOiAiMjQ4Mjg5NzYxMDAxIiwKICJhdWQiOiAiczZCaGRSa3F0MyIsCiAibm9uY2UiOiAibi0wUzZfV3pBMk1qIiwKICJleHAiOiAxMzExMjgxOTcwLAogImlhdCI6IDEzMTEyODA5NzAsCiAiY19oYXNoIjogIkxEa3RLZG9RYWszUGswY25YeENsdEEiCn0.XW6uhdrkBgcGx6zVIrCiROpWURs-4goO1sKA4m9jhJIImiGg5muPUcNegx6sSv43c5DSn37sxCRrDZZm4ZPBKKgtYASMcE20SDgvYJdJS0cyuFw7Ijp_7WnIjcrl6B5cmoM6ylCvsLMwkoQAxVublMwH10oAxjzD6NEFsu9nipkszWhsPePf_rM4eMpkmCbTzume-fzZIi5VjdWGGEmzTg32h3jiex-r5WTHbj-u5HL7u_KP3rmbdYNzlzd1xWRYTUs4E8nOTgzAUwvwXkIQhOh5TPcSMBYy6X3E7-_gr9Ue6n4ND7hTFhtjYs3cjNKIA08qm5cpVYFMFMG6PkhzLQ";
RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
rsa.ImportParameters(
new RSAParameters()
{
Modulus = FromBase64Url("w7Zdfmece8iaB0kiTY8pCtiBtzbptJmP28nSWwtdjRu0f2GFpajvWE4VhfJAjEsOcwYzay7XGN0b-X84BfC8hmCTOj2b2eHT7NsZegFPKRUQzJ9wW8ipn_aDJWMGDuB1XyqT1E7DYqjUCEOD1b4FLpy_xPn6oV_TYOfQ9fZdbE5HGxJUzekuGcOKqOQ8M7wfYHhHHLxGpQVgL0apWuP2gDDOdTtpuld4D2LK1MZK99s9gaSjRHE8JDb1Z4IGhEcEyzkxswVdPndUWzfvWBBWXWxtSUvQGBRkuy1BHOa4sP6FKjWEeeF7gm7UMs2Nm2QUgNZw6xvEDGaLk4KASdIxRQ"),
Exponent = FromBase64Url("AQAB")
});
var validationParameters = new TokenValidationParameters
{
RequireExpirationTime = true,
RequireSignedTokens = true,
ValidateAudience = false,
ValidateIssuer = false,
ValidateLifetime = false,
IssuerSigningKey = new RsaSecurityKey(rsa)
};
SecurityToken validatedSecurityToken = null;
var handler = new JwtSecurityTokenHandler();
handler.ValidateToken(tokenStr, validationParameters, out validatedSecurityToken);
JwtSecurityToken validatedJwt = validatedSecurityToken as JwtSecurityToken;

For anyone that is looking for a quick method to validate RS256 with a public key that has "-----BEGIN PUBLIC KEY-----"/"-----END PUBLIC KEY------"
Here are two methods with the help of BouncyCastle.
public bool ValidateJasonWebToken(string fullKey, string jwtToken)
{
try
{
var rs256Token = fullKey.Replace("-----BEGIN PUBLIC KEY-----", "");
rs256Token = rs256Token.Replace("-----END PUBLIC KEY-----", "");
rs256Token = rs256Token.Replace("\n", "");
Validate(jwtToken, rs256Token);
return true;
}
catch (Exception e)
{
Console.WriteLine(e);
return false;
}
}
private void Validate(string token, string key)
{
var keyBytes = Convert.FromBase64String(key); // your key here
AsymmetricKeyParameter asymmetricKeyParameter = PublicKeyFactory.CreateKey(keyBytes);
RsaKeyParameters rsaKeyParameters = (RsaKeyParameters)asymmetricKeyParameter;
RSAParameters rsaParameters = new RSAParameters
{
Modulus = rsaKeyParameters.Modulus.ToByteArrayUnsigned(),
Exponent = rsaKeyParameters.Exponent.ToByteArrayUnsigned()
};
using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
{
rsa.ImportParameters(rsaParameters);
var validationParameters = new TokenValidationParameters()
{
RequireExpirationTime = false,
RequireSignedTokens = true,
ValidateAudience = false,
ValidateIssuer = false,
IssuerSigningKey = new RsaSecurityKey(rsa)
};
var handler = new JwtSecurityTokenHandler();
var result = handler.ValidateToken(token, validationParameters, out var validatedToken);
}
}
This is a combination of http://codingstill.com/2016/01/verify-jwt-token-signed-with-rs256-using-the-public-key/ and #olaf answer that uses system.IdentityModel.Tokens.Jwt

NET Core
To use this in a .NET core web api (.NET Framework see below) in a AddJwtBearer() auth flow I enhanced NvMat's great answer:
Very important is to not use the RSACryptoServiceProvider in an using statement.
private TokenValidationParameters GetTokenValidationParameters(string key)
{
var rs256Token = key.Value.Replace("-----BEGIN PUBLIC KEY-----", "");
rs256Token = rs256Token.Replace("-----END PUBLIC KEY-----", "");
rs256Token = rs256Token.Replace("\n", "");
var keyBytes = Convert.FromBase64String(rs256Token);
var asymmetricKeyParameter = PublicKeyFactory.CreateKey(keyBytes);
var rsaKeyParameters = (RsaKeyParameters)asymmetricKeyParameter;
var rsaParameters = new RSAParameters
{
Modulus = rsaKeyParameters.Modulus.ToByteArrayUnsigned(),
Exponent = rsaKeyParameters.Exponent.ToByteArrayUnsigned()
};
var rsa = new RSACryptoServiceProvider();
rsa.ImportParameters(rsaParameters);
var validationParameters = new TokenValidationParameters()
{
RequireExpirationTime = false,
RequireSignedTokens = true,
ValidateAudience = false,
ValidateIssuer = false,
IssuerSigningKey = new RsaSecurityKey(rsa),
};
return validationParameters;
}
Then you are able to use authentication in the startup like this:
services.AddAuthentication(x =>
{
x.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
x.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
})
.AddJwtBearer(options =>
{
options.RequireHttpsMetadata = false;
options.SaveToken = true;
options.IncludeErrorDetails = true;
options.TokenValidationParameters = GetTokenValidationParameters(configuration["Key"]);
options.Audience = configuration["ClientId"];
});
NET Framework
It is also possible to use this approach in a .NET Framework web api project. All you have to do is add this line to your startup Configure() method:
app.UseJwtBearerAuthentication(new JwtBearerAuthenticationOptions()
{
TokenValidationParameters = GetTokenValidationParameters(ConfigurationManager.AppSettings["Key"])
});
One important thing: Make sure you use a verion >=5.0.0 of the JwtSecurityTokenHandler
I had problems with the 4.X.X versions.

You can do this very easily with Jwt.Net. This function will decode and verify the signature of a JWT and return the payload as a dictionary of claims:
private IDictionary<string, object> Decode(string token, string modulus, string exponent)
{
var urlEncoder = new JwtBase64UrlEncoder();
var rsaKey = RSA.Create();
rsaKey.ImportParameters(new RSAParameters() {
Modulus = urlEncoder.Decode(modulus),
Exponent = urlEncoder.Decode(exponent)
});
var claims = new JwtBuilder()
.WithAlgorithm(new RS256Algorithm(rsaKey))
.MustVerifySignature()
.Decode<IDictionary<string, object>>(token);
return claims;
}
Sample use:
string jwt = "eyJraWQiOiIxZTlnZGs3IiwiYWxnIjoiUlMyNTYifQ.ewogImlzcyI6ICJodHRwOi8vc2VydmVyLmV4YW1wbGUuY29tIiwKICJzdWIiOiAiMjQ4Mjg5NzYxMDAxIiwKICJhdWQiOiAiczZCaGRSa3F0MyIsCiAibm9uY2UiOiAibi0wUzZfV3pBMk1qIiwKICJleHAiOiAxMzExMjgxOTcwLAogImlhdCI6IDEzMTEyODA5NzAsCiAiY19oYXNoIjogIkxEa3RLZG9RYWszUGswY25YeENsdEEiCn0.XW6uhdrkBgcGx6zVIrCiROpWURs-4goO1sKA4m9jhJIImiGg5muPUcNegx6sSv43c5DSn37sxCRrDZZm4ZPBKKgtYASMcE20SDgvYJdJS0cyuFw7Ijp_7WnIjcrl6B5cmoM6ylCvsLMwkoQAxVublMwH10oAxjzD6NEFsu9nipkszWhsPePf_rM4eMpkmCbTzume-fzZIi5VjdWGGEmzTg32h3jiex-r5WTHbj-u5HL7u_KP3rmbdYNzlzd1xWRYTUs4E8nOTgzAUwvwXkIQhOh5TPcSMBYy6X3E7-_gr9Ue6n4ND7hTFhtjYs3cjNKIA08qm5cpVYFMFMG6PkhzLQ";
string modulus = "w7Zdfmece8iaB0kiTY8pCtiBtzbptJmP28nSWwtdjRu0f2GFpajvWE4VhfJAjEsOcwYzay7XGN0b-X84BfC8hmCTOj2b2eHT7NsZegFPKRUQzJ9wW8ipn_aDJWMGDuB1XyqT1E7DYqjUCEOD1b4FLpy_xPn6oV_TYOfQ9fZdbE5HGxJUzekuGcOKqOQ8M7wfYHhHHLxGpQVgL0apWuP2gDDOdTtpuld4D2LK1MZK99s9gaSjRHE8JDb1Z4IGhEcEyzkxswVdPndUWzfvWBBWXWxtSUvQGBRkuy1BHOa4sP6FKjWEeeF7gm7UMs2Nm2QUgNZw6xvEDGaLk4KASdIxRQ";
string exponent = "AQAB";
try
{
IDictionary<string, object> claims = Decode(jwt, modulus, exponent);
}
catch (SignatureVerificationException)
{
// signature invalid, handle it here
}

.NET JWT Signature Verification using System.Security.Cryptography - No 3rd Party DLLs
var errorMessage = string.Empty;
// Google RSA well known Public Key data is available at https://accounts.google.com/.well-known/openid-configuration by navigating to the path described in the "jwks_uri" parameter.
// {
// e: "AQAB", // RSA Exponent
// n: "ya_7gV....", // RSA Modulus aka Well Known Public Key
// alg: "RS256" // RSA Algorithm
// }
var verified = VerifyJWT_RS256_Signature(
jwt: "oicjwt....",
publicKey: "ya_7gV....",
exponent: "AQAB",
errorMessage: out errorMessage);
if (!verified)
{
// TODO: log error:
// TODO: Do something
}
NOTE: The following method verifies OpenID Connect JWT Signatures signed with Asymetric RS256 keys. OpenID Connect providers may opt to use other versions of Asymetric keys or even Symetric keys like HS256. This method does not directly support other key types.
public static bool VerifyJWT_RS256_Signature(string jwt, string publicKey, string exponent, out string errorMessage)
{
if (string.IsNullOrEmpty(jwt))
{
errorMessage = "Error verifying JWT token signature: Javascript Web Token was null or empty.";
return false;
}
var jwtArray = jwt.Split('.');
if (jwtArray.Length != 3 && jwtArray.Length != 5)
{
errorMessage = "Error verifying JWT token signature: Javascript Web Token did not match expected format. Parts count was " + jwtArray.Length + " when it should have been 3 or 5.";
return false;
}
if (string.IsNullOrEmpty(publicKey))
{
errorMessage = "Error verifying JWT token signature: Well known RSA Public Key modulus was null or empty.";
return false;
}
if (string.IsNullOrEmpty(exponent))
{
errorMessage = "Error verifying JWT token signature: Well known RSA Public Key exponent was null or empty.";
return false;
}
try
{
string publicKeyFixed = (publicKey.Length % 4 == 0 ? publicKey : publicKey + "====".Substring(publicKey.Length % 4)).Replace("_", "/").Replace("-", "+");
var publicKeyBytes = Convert.FromBase64String(publicKeyFixed);
var jwtSignatureFixed = (jwtArray[2].Length % 4 == 0 ? jwtArray[2] : jwtArray[2] + "====".Substring(jwtArray[2].Length % 4)).Replace("_", "/").Replace("-", "+");
var jwtSignatureBytes = Convert.FromBase64String(jwtSignatureFixed);
RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
rsa.ImportParameters(
new RSAParameters()
{
Modulus = publicKeyBytes,
Exponent = Convert.FromBase64String(exponent)
}
);
SHA256 sha256 = SHA256.Create();
byte[] hash = sha256.ComputeHash(Encoding.UTF8.GetBytes(jwtArray[0] + '.' + jwtArray[1]));
RSAPKCS1SignatureDeformatter rsaDeformatter = new RSAPKCS1SignatureDeformatter(rsa);
rsaDeformatter.SetHashAlgorithm("SHA256");
if (!rsaDeformatter.VerifySignature(hash, jwtSignatureBytes))
{
errorMessage = "Error verifying JWT token signature: hash did not match expected value.";
return false;
}
}
catch (Exception ex)
{
errorMessage = "Error verifying JWT token signature: " + ex.Message;
return false;
//throw ex;
}
errorMessage = string.Empty;
return true;
}
NOTE: Verifying the signature of an OpenID Connect JWT (Javascript Web Token) is only one necessary step of the JWT verification process. Make sure to set a NONCE value which your system can use to prevent Replay attacks. Make sure to validate each parameter of the JWT package for completeness and accuracy.

Try to use JwtUtils nuget package
It has pretty simple API:
string publicKey = "#MIIJKgIBAAKCAgEA9GF97STxVGbXpBFmudS/RRT58mfiR/+t2zb4f/uF3qmYb
yuJy2v8xOMbHvMkoKLPLc590zGV88HNvzJHkF5N5HWTB9ZZEWcehf6RcTA==";
if (JWT.RS256.ValidateSignature("{YOUR_JWT_TOKEN}", publicKey))
{
// Token signature valid
}

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