我必须传递来自 CMSSignedData 对象的哪些数据才能生成有效的时间戳？

Question

我已将有效的 PKCS7 文件加载到 CMSSignedData 对象中。此 PKCS7 文件包括一个纯文本消息和一个有效的附加数字签名（都在同一个文件中）。

现在我想给这个文件加上时间戳。这是我使用的代码 (source):

 private static CMSSignedData addTimestamp(CMSSignedData signedData)
throws Exception {
        Collection ss = signedData.getSignerInfos().getSigners();
        SignerInformation si = (SignerInformation) ss.iterator().next();

        TimeStampToken tok = getTimeStampToken();

        ASN1InputStream asn1InputStream = new ASN1InputStream
(tok.getEncoded());
        DERObject tstDER = asn1InputStream.readObject();
        DERSet ds = new DERSet(tstDER);

        Attribute a = new Attribute(new
DERObjectIdentifier("1.2.840.113549.1.9.16.2.14"), ds);
        DEREncodableVector dv = new DEREncodableVector();
        dv.add(a);
        AttributeTable at = new AttributeTable(dv);
        si = SignerInformation.replaceUnsignedAttributes(si, at);
        ss.clear();
        ss.add(si);
        SignerInformationStore sis = new SignerInformationStore(ss);

        signedData = CMSSignedData.replaceSigners(signedData, sis);
        return signedData;
    }


 private static TimeStampToken getTimeStampToken() throws
Exception {
        Security.addProvider (new
org.bouncycastle.jce.provider.BouncyCastleProvider());

        PostMethod post = new PostMethod("http://My-TrustedTimeStampProvier.com");

// I'm omitting the part where I pass the user and password

        TimeStampRequestGenerator reqGen = new TimeStampRequestGenerator();
        //request TSA to return certificate
        reqGen.setCertReq (true); // In my case this works

        //make a TSP request this is a dummy sha1 hash (20 zero bytes)
        TimeStampRequest request =
            reqGen.generate(TSPAlgorithms.SHA1, new byte[20], BigInteger.valueOf(100));

        byte[] enc_req = request.getEncoded();
        ByteArrayInputStream bais = new ByteArrayInputStream(enc_req);

        post.setRequestBody(bais);
        post.setRequestContentLength (enc_req.length);
        post.setRequestHeader("Content-type","application/timestamp-query");

        HttpClient http_client = new HttpClient();
        http_client.executeMethod(post);
        InputStream in = post.getResponseBodyAsStream();

        //read TSP response
        TimeStampResponse resp = new TimeStampResponse (in);

        resp.validate(request);

        TimeStampToken  tsToken = resp.getTimeStampToken();       
        return tsToken;
    }

我可以获得一个有效的时间戳，我可以将它放入我的 CMSSignedData 对象并将其保存到一个文件中，将 signedData.getEncoded() 中的字节写入硬盘。但是当我用 third party software 验证我新的带有时间戳的新文件时，该软件告诉原始签名没问题，但时间戳与签名不一致。这个软件还可以给我显示原始的纯文本消息。

我认为问题出在这一行：

TimeStampRequest request =
    reqGen.generate(TSPAlgorithms.SHA1, new byte[20], BigInteger.valueOf(100));

我想我必须传递摘要而不是虚拟字节数组，但我不知道哪个摘要，或者我必须给时间戳记的正确字节是什么。我成功地从我的 signedData 中获取并验证了一个 SignerInformation 对象。然后我尝试将来自 mySignerInformation.getSignature() 的字节传递给 reqGen.generate() 函数。时间戳验证失败。然后我通过了一个mySignerInformation.getSignature()的Sha1摘要，但是我的时间戳验证又失败了

RFC3161 specification 说：

2.4.1. Request Format

A time-stamping request is as follows:

TimeStampReq ::= SEQUENCE { version INTEGER { v1(1) }, messageImprint MessageImprint, --a hash algorithm OID and the hash value of the data to be

(...)

The messageImprint field SHOULD contain the hash of the datum to be time-stamped. The hash is represented as an OCTET STRING. Its
length MUST match the length of the hash value for that algorithm
(e.g., 20 bytes for SHA-1 or 16 bytes for MD5).

MessageImprint ::= SEQUENCE { hashAlgorithm AlgorithmIdentifier, hashedMessage OCTET STRING }

但是如果我想在 CMSSignedData 对象中的字节上加时间戳，它不会告诉我在哪里或如何获取 MessageImprint 数据。

我是数字签名方面的新手。

Answer 1

你是对的，问题是你给不正确的数据加了时间戳。其余代码对我来说似乎是正确的。

所以问题是您必须为签名的散列加上时间戳。从您的 CMSSignedData 获取签名并对其进行哈希处理；您可以使用以下代码（假设您的 PKCS7 中只有一个签名者并且您使用的是 SHA1 哈希算法）：

CMSSignedData signedData = ...
// get the signers of your CMSSignedData signedData
Collection ss = signedData.getSignerInfos().getSigners();
SignerInformation si = (SignerInformation) ss.iterator().next();
// hash the signature
byte[] signDigest = MessageDigest
      .getInstance(TSPAlgorithms.SHA1, new BouncyCastleProvider())
      .digest(si.getSignature()); // since you're adding the bc provider with Security.addProvider you can use "BC" instead of passing the new BouncyCastleProvider() 
TimeStampRequestGenerator reqGen = new TimeStampRequestGenerator();
// generate the TSRequest
TimeStampRequest request =
            reqGen.generate(TSPAlgorithms.SHA1, signDigest, BigInteger.valueOf(100));
...

希望这对您有所帮助，

我必须传递来自 CMSSignedData 对象的哪些数据才能生成有效的时间戳？

Which data from a CMSSignedData object must I pass to generate a valid Timestamp?

java

validation

bouncycastle

trusted-timestamp

pkcs#7