在我的构建过程中，我想包含来自符合 RFC-3161 的 TSA 的时间戳。在运行时，代码将验证这个时间戳，最好不需要第三方库的帮助。（这是一个 .NET 应用程序，因此我可以随时使用标准哈希和非对称加密功能。）
RFC 3161 依赖于 ASN.1 和 X.690 等等，实现起来并不简单，所以至少现在，我使用 Bouncy Castle 来生成 TimeStampReq（请求）并解析 TimeStampResp（响应）。我只是无法弄清楚如何验证响应。
到目前为止，我已经弄清楚了如何提取签名本身、公共证书、创建时间戳的时间以及我发送的消息印记摘要和随机数（用于构建时验证）。我不知道如何将这些数据放在一起以生成经过散列和签名的数据。
这是我正在做什么以及我正在尝试做什么的粗略想法。这是测试代码，所以我采取了一些捷径。一旦我得到一些有用的东西，我将不得不清理一些东西并以正确的方式做它们。
构建时生成时间戳：
// a lot of fully-qualified type names here to make sure it's clear what I'm using
static void WriteTimestampToBuild(){
var dataToTimestamp = Encoding.UTF8.GetBytes("The rain in Spain falls mainly on the plain");
var hashToTimestamp = new System.Security.Cryptography.SHA1Cng().ComputeHash(dataToTimestamp);
var nonce = GetRandomNonce();
var tsr = GetTimestamp(hashToTimestamp, nonce, "http://some.rfc3161-compliant.server");
var tst = tsr.TimeStampToken;
var tsi = tst.TimeStampInfo;
ValidateNonceAndHash(tsi, hashToTimestamp, nonce);
var cms = tst.ToCmsSignedData();
var signer =
cms.GetSignerInfos().GetSigners()
.Cast<Org.BouncyCastle.Cms.SignerInformation>().First();
// TODO: handle multiple signers?
var signature = signer.GetSignature();
var cert =
tst.GetCertificates("Collection").GetMatches(signer.SignerID)
.Cast<Org.BouncyCastle.X509.X509Certificate>().First();
// TODO: handle multiple certs (for one or multiple signers)?
ValidateCert(cert);
var timeString = tsi.TstInfo.GenTime.TimeString;
var time = tsi.GenTime; // not sure which is more useful
// TODO: Do I care about tsi.TstInfo.Accuracy or tsi.GenTimeAccuracy?
var serialNumber = tsi.SerialNumber.ToByteArray(); // do I care?
WriteToBuild(cert.GetEncoded(), signature, timeString/*or time*/, serialNumber);
// TODO: Do I need to store any more values?
}
static Org.BouncyCastle.Math.BigInteger GetRandomNonce(){
var rng = System.Security.Cryptography.RandomNumberGenerator.Create();
var bytes = new byte[10]; // TODO: make it a random length within a range
rng.GetBytes(bytes);
return new Org.BouncyCastle.Math.BigInteger(bytes);
}
static Org.BouncyCastle.Tsp.TimeStampResponse GetTimestamp(byte[] hash, Org.BouncyCastle.Math.BigInteger nonce, string url){
var reqgen = new Org.BouncyCastle.Tsp.TimeStampRequestGenerator();
reqgen.SetCertReq(true);
var tsrequest = reqgen.Generate(Org.BouncyCastle.Tsp.TspAlgorithms.Sha1, hash, nonce);
var data = tsrequest.GetEncoded();
var webreq = WebRequest.CreateHttp(url);
webreq.Method = "POST";
webreq.ContentType = "application/timestamp-query";
webreq.ContentLength = data.Length;
using(var reqStream = webreq.GetRequestStream())
reqStream.Write(data, 0, data.Length);
using(var respStream = webreq.GetResponse().GetResponseStream())
return new Org.BouncyCastle.Tsp.TimeStampResponse(respStream);
}
static void ValidateNonceAndHash(Org.BouncyCastle.Tsp.TimeStampTokenInfo tsi, byte[] hashToTimestamp, Org.BouncyCastle.Math.BigInteger nonce){
if(tsi.Nonce != nonce)
throw new Exception("Nonce doesn't match. Man-in-the-middle attack?");
var messageImprintDigest = tsi.GetMessageImprintDigest();
var hashMismatch =
messageImprintDigest.Length != hashToTimestamp.Length ||
Enumerable.Range(0, messageImprintDigest.Length).Any(i=>
messageImprintDigest[i] != hashToTimestamp[i]
);
if(hashMismatch)
throw new Exception("Message imprint doesn't match. Man-in-the-middle attack?");
}
static void ValidateCert(Org.BouncyCastle.X509.X509Certificate cert){
// not shown, but basic X509Chain validation; throw exception on failure
// TODO: Validate certificate subject and policy
}
static void WriteToBuild(byte[] cert, byte[] signature, string time/*or DateTime time*/, byte[] serialNumber){
// not shown
}
运行时的时间戳验证（客户端站点）：
// a lot of fully-qualified type names here to make sure it's clear what I'm using
static void VerifyTimestamp(){
var timestampedData = Encoding.UTF8.GetBytes("The rain in Spain falls mainly on the plain");
var timestampedHash = new System.Security.Cryptography.SHA1Cng().ComputeHash(timestampedData);
byte[] certContents;
byte[] signature;
string time; // or DateTime time
byte[] serialNumber;
GetDataStoredDuringBuild(out certContents, out signature, out time, out serialNumber);
var cert = new System.Security.Cryptography.X509Certificates.X509Certificate2(certContents);
ValidateCert(cert);
var signedData = MagicallyCombineThisStuff(timestampedHash, time, serialNumber);
// TODO: What other stuff do I need to magically combine?
VerifySignature(signedData, signature, cert);
// not shown: Use time from timestamp to validate cert for other signed data
}
static void GetDataStoredDuringBuild(out byte[] certContents, out byte[] signature, out string/*or DateTime*/ time, out byte[] serialNumber){
// not shown
}
static void ValidateCert(System.Security.Cryptography.X509Certificates.X509Certificate2 cert){
// not shown, but basic X509Chain validation; throw exception on failure
}
static byte[] MagicallyCombineThisStuff(byte[] timestampedhash, string/*or DateTime*/ time, byte[] serialNumber){
// HELP!
}
static void VerifySignature(byte[] signedData, byte[] signature, System.Security.Cryptography.X509Certificates.X509Certificate2 cert){
var key = (RSACryptoServiceProvider)cert.PublicKey.Key;
// TODO: Handle DSA keys, too
var okay = key.VerifyData(signedData, CryptoConfig.MapNameToOID("SHA1"), signature);
// TODO: Make sure to use the same hash algorithm as the TSA
if(!okay)
throw new Exception("Timestamp doesn't match! Don't trust this!");
}
正如您可能猜到的那样，我认为我被卡住的地方是MagicallyCombineThisStuff功能。