amazon-web-services - AWS KMS 签名为我的 JWT 返回无效签名

Question

我正在尝试使用 ES256 和 KMS 生成一个简单的 JWT。肉眼看起来一切都很好。但是当我通过 jwt.io 测试它时，我得到了“无效签名”。代码非常简单:

public async Task<string> GenerateJwt(object payload)
{
    var encodedHeader = Base64Encoder.EncodeBase64Url(JsonSerializer.Serialize(_header));
    var encodedPayload = Base64Encoder.EncodeBase64Url(JsonSerializer.Serialize(payload));

    var signatureData = Encoding.ASCII.GetBytes(encodedHeader + "." + encodedPayload);

    var signature = await _signingService.Sign(signatureData);
    var encodedSignature = Base64Encoder.ReplaceSpecialUrlCharacters(Convert.ToBase64String(signature));

    return encodedHeader + "." + encodedPayload + "." + encodedSignature;
}

SigningService 看起来像这样:

public async Task<byte[]> Sign(byte[] signatureData)
{
    using var memoryStream = new MemoryStream(signatureData, 0, signatureData.Length);
    var signRequest = new SignRequest()
    {
        KeyId = _signingKeyId,
        Message = memoryStream,
        SigningAlgorithm = SigningAlgorithmSpec.ECDSA_SHA_256
    };
    SignResponse signResponse = await _keyManagementService.SignAsync(signRequest);
    return signResponse.Signature.ToArray();
}

_keyManagementService 是来自 AWSSDK.KeyManagementService 3.5.2.6 的 IAamazonKeyManagementService

在 KMS 中， key 是这样设置的:

• 关键规范:ECC_NIST_P256
• key 用法:签名和验证
• 签名算法:ECDSA_SHA_256

KMS 中的公钥(使用 localstack)

MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEj7Cy/Gbx3jnuPdanuBSjuUmdnr7tQ/BcOytDlFoHWdNA1scc6RwNwqnNbmRE0BmwnlFNDVGxWU5oycTig8p0KQ==

生成的输出示例

eyJhbGciOiJFUzI1NiJ9.eyJ0ZXN0MSI6MSwidGVzdDIiOiJ0d28iLCJ0ZXN0MyI6ZmFsc2V9.MEYCIQCiatnRhYGBKgdJj9LECe7mJ4bhhkVTvFSgpVI3Dm14pwIhAOrHAu0vqKvVwdgpAhaU7KOhiIBZdcEOuzfXrdXldCFQ

如果它使用内置工具(只需替换上面的 signatureData 行)使用相同的输入对其进行签名，我就会在 jwt.io 中对其进行验证。

var ecdsa = ECDsa.Create();
ecdsa.GenerateKey(ECCurve.NamedCurves.nistP256);
var signatureData = ecdsa.SignData(signatureData, HashAlgorithmName.SHA256);

任何输入都将受到欢迎，因为感觉我已经测试了所有内容...

Answer 1

问题是 KMS 以另一种格式返回签名:

DER-encoded object as defined by ANS X9.62–2005

虽然 JWT 应该采用 R || 格式S 根据 https://www.rfc-editor.org/rfc/rfc7515#appendix-A.3.1

所以我所做的是使用 BouncyCaSTLe 添加一个转换方法，并在将其转换为 base64url 之前调用它:

private byte[] ConvertSignature(byte[] signature)
{
    var asn1 = Asn1Object.FromByteArray(signature) as DerSequence;
    if (asn1 == null)
        return Array.Empty<byte>();

    if (asn1.Count < 2)
        return Array.Empty<byte>();

    var r = asn1[0] as DerInteger;
    var s = asn1[1] as DerInteger;

    if (r == null || s == null)
        return Array.Empty<byte>();

    return Array.Empty<byte>()
        .Concat(r.Value.ToByteArrayUnsigned())
        .Concat(s.Value.ToByteArrayUnsigned())
        .ToArray();
}