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