c# - ES 512 jwt token 验证

Question

我正在尝试使用字符串格式的公钥验证 ES512 jwt token :
我正在尝试模仿为 ES256 编写的示例
这是这样的:

    // The code for ES256
    public static void VerifyES512Jwt(string token,string publicKey)
    {
        byte[] publicKeyBytes = Convert.FromBase64String(publicKey);

        string[] parts = token.Split('.');

        string header = parts[0];
        string payload = parts[1];
        string signature = parts[2];

        var keyType = new byte[] { 0x45, 0x43, 0x53, 0x31 };
        var keyLength = new byte[] { 0x20, 0x00, 0x00, 0x00 };
        var key = keyType.Concat(keyLength).Concat(publicKeyBytes.Skip(publicKeyBytes.Length - 64)).ToArray(); 
        CngKey cngKey = CngKey.Import(key, CngKeyBlobFormat.EccPublicBlob);
        
        // the purpose is to get ECDsaCng and verify the payload data
         ECDsaCng eCDsaCng = new ECDsaCng(cngKey);
        
        bool result = eCDsaCng.VerifyData(payload, signatureBytes); 
    }

我正在尝试将此代码用于 ES512 并卡在获取 key 上

        var keyType = new byte[] { 0x45, 0x43, 0x53, 0x31 };
        var keyLength = new byte[] { 0x20, 0x00, 0x00, 0x00 };
        var key = keyType.Concat(keyLength).Concat(publicKeyBytes.Skip(publicKeyBytes.Length - 64)).ToArray(); 

当与上述一起使用时，它会在获取 key 时出错:

CngKey cngKey = CngKey.Import(key, CngKeyBlobFormat.EccPublicBlob);

我使用的公钥和 token 如下:
公钥:

MIGbMBAGByqGSM49AgEGBSuBBAAjA4GGAAQBgc4HZz+/fBbC7lmEww0AO3NK9wVZPDZ0VEnsaUFLEYpTzb90nITtJUcPUbvOsdZIZ1Q8fnbquAYgxXL5UgHMoywAib476MkyyYgPk0BXZq3mq4zImTRNuaU9slj9TVJ3ScT3L1bXwVuPJDzpr5GOFpaj+WwMAl8G7CqwoJOsW7Kddns=

代币:

eyJ0eXAiOiJKV1QiLCJhbGciOiJFUzUxMiJ9.eyJpc3MiOiJPbmxpbmUgSldUIEJ1aWxkZXIiLCJpYXQiOjE1NjUwOTk2ODgsImV4cCI6MTU5ODE4OTg4NSwiYXVkIjoiaHR0cDovL2xvY2FsaG9zdDozNTg4Iiwic3ViIjoiaHR0cDovL2xvY2FsaG9zdDo1MDM3NiIsImZpcnN0bmFtZSI6IkFydmluZCIsImxhc3RuYW1lIjoiS3VtYXIiLCJFbWFpbCI6ImFydmluZC5rdW1hckBzdHJlYW1hbWcuY29tIiwiSWQiOiIxMDEifQ.AVwAJeY44lKrnywnDs7CdUOu3gli2cGafSJ6iP3zT7lkZpd2QnL0k54aVmPVxAGuN5dDnzbYmMTdRl5u2QE92ccOAHrcf5yA2gsvhhAGuDAAeh6Io4VU7v5TOTvwWGRb-ubgdjUvagA_HSJOyeXvFR16_M_MzGfDnXfg02sj4y9VFjDr

Answer 1

ES512使用带有 P-521 和 SHA-512 的 ECDSA。
P-521 的公钥( secp521r1 ，第 2.6.1 章)的大小为 2 x 66 = 132未压缩形式的字节(前字节 0x04 )。 MS 使用值 0x35534345 指定 P-521 的公钥.
因此，必须按如下方式生成 key :

var keyType = new byte[] { 0x45, 0x43, 0x53, 0x35 };
var keyLength = new byte[] { 0x42, 0x00, 0x00, 0x00 };
var key = keyType.Concat(keyLength).Concat(publicKeyBytes.Skip(publicKeyBytes.Length - 132)).ToArray();

要签名的数据是 header 和有效负载(都是 Base64url 编码的)，包括分隔符 ( . )。签名也是 Base64url 编码的。因此，必须按以下方式进行验证:

byte[] headerPayloadBytes = Encoding.UTF8.GetBytes(header + "." + payload);
byte[] signatureBytes = Base64UrlDecode(signature);
bool verified = eCDsaCng.VerifyData(headerPayloadBytes, signatureBytes, HashAlgorithmName.SHA512);

Base64UrlDecode完成 Base64url 解码，参见例如 here实现细则。