使用C#中的公钥验证使用RS256算法签名的JWT

感谢jwilleke，我有了一个解决方案。要验证JWT的RS256签名，需要使用RSAPKCS1SignatureDeformatter类及其VerifySignature方法。

这是我的样本数据的确切代码：

  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);
  }

以下是使用IdentityModel.Tokens.Jwt进行验证的示例：

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;

对于任何正在寻找一种快速方法来验证RS256的人，该方法的公钥具有"-----BEGIN public key------"/"-----END public key------"

以下是在BouncyCastle的帮助下的两种方法。

    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);
        }
    }

这是http://codingstill.com/2016/01/verify-jwt-token-signed-with-rs256-using-the-public-key/和使用system.IdentityModel.Tokens.Jwt 的@olaf应答

NET Core

要在AddJwtBearer()身份验证流中的.NET核心web api（.NET Framework见下文）中使用它，我增强了NvMat的伟大答案：

非常重要的是不要在using语句中使用RSACryptoServiceProvider。

    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;
    }

然后你就可以像这样在启动中使用身份验证：

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框架

在.NET Framework web api项目中也可以使用这种方法。你所要做的就是将这一行添加到你的启动Configure()方法中：

app.UseJwtBearerAuthentication(new JwtBearerAuthenticationOptions()
{
     TokenValidationParameters = GetTokenValidationParameters(ConfigurationManager.AppSettings["Key"])
});

一件重要的事情：确保使用JwtSecurityTokenHandler的版本>=5.0我的4.X.X版本有问题。

使用Jwt.Net可以很容易地完成此操作。此函数将解码和验证Jwt的签名，并将有效载荷作为声明字典返回：

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;
}

样品用途：

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签名验证使用System.Security.Cryptography-无第三方DLL

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
}

注意：以下方法验证使用Asymetric RS256密钥签名的OpenID Connect JWT签名。OpenID Connect提供商可以选择使用其他版本的Asymetric密钥，甚至像HS256这样的Symmetric密钥。此方法不直接支持其他键类型。

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;
}

注：验证OpenID Connect JWT（Javascript Web令牌）的签名只是JWT验证过程中的一个必要步骤。请确保设置一个NONCE值，系统可以使用该值来防止Replay攻击。确保验证JWT包的每个参数的完整性和准确性。

尝试使用JwtUtilsnuget包它有非常简单的API：

string publicKey = "@MIIJKgIBAAKCAgEA9GF97STxVGbXpBFmudS/RRT58mfiR/+t2zb4f/uF3qmYb
yuJy2v8xOMbHvMkoKLPLc590zGV88HNvzJHkF5N5HWTB9ZZEWcehf6RcTA==";
if (JWT.RS256.ValidateSignature("{YOUR_JWT_TOKEN}", publicKey))
{
   // Token signature valid
}