CODEWITHSUNDEEP
c#bouncycastle
Victor
Victor

Reputation: 23972

How do I get the signature in a TimeStampToken (Bouncy Castle)

From RFC 3852 (and RFC 3161) I understand that the signature value is stored as an attribute of the SignerInfo type of the TimestampToken (which is a Signed Data content type).

How can I get that signature value from a TimeStampToken instance of Bouncy Castle (in C#)?

Upvotes: 2

Views: 1961

Answers (2)

Victor
Victor

Reputation: 23972

I was able to get the signature using this:

CmsSignedData tsTokenCms = timestampToken.ToCmsSignedData();
SignerInformationStore signerInfoStore = tsTokenCms.GetSignerInfos();
SignerInformation signerInfo = signerInfoStore.GetFirstSigner(timestampToken.SignerID);
byte[] signatureBytes = signerInfo.GetSignature();
string signatureString = BitConverter.ToString(signatureBytes);
Console.WriteLine("Signature is: " + signatureString);

Upvotes: 1

hal
hal

Reputation: 1757

You could use class with helper methods:

public static class TimeStampTokenHelper
{
    public static IEnumerable<SignedData> GetTimeStampTokensAsSignedData(byte[] input)
    {
        var cmsInputStream = new Asn1InputStream(input);
        var asn1Object = cmsInputStream.ReadObject();
        Assert.IsNotNull(asn1Object);

        var rootSequence = Asn1Sequence.GetInstance(asn1Object);
        var signedData = GetSignedData(rootSequence);
        return GetTimeStampTokensFromSignedData(signedData);
    }

    private static SignedData GetSignedData(Asn1Sequence sequence)
    {
        var rootContent = ContentInfo.GetInstance(sequence);
        Assert.That(rootContent.ContentType.Id, Is.EqualTo("1.2.840.113549.1.7.2")); // signedData
        var signedData = SignedData.GetInstance(rootContent.Content);
        return signedData;
    }

    private static IEnumerable<SignedData> GetTimeStampTokensFromSignedData(SignedData signedData)
    {
        return GetTimeStampTokensFromSignerInfos(signedData.SignerInfos);
    }

    private static IEnumerable<SignedData> GetTimeStampTokensFromSignerInfos(Asn1Set signerInfos)
    {
        var timestampTokens = signerInfos
            .OfType<Asn1Sequence>()
            .SelectMany(GetTimeStampTokensFromSignerInfo);
        return timestampTokens;
    }

    private static IEnumerable<SignedData> GetTimeStampTokensFromSignerInfo(Asn1Sequence signerInfoSequence)
    {
        var signerInfo = SignerInfo.GetInstance(signerInfoSequence);
        var result = signerInfo.UnauthenticatedAttributes.ToArray()
            .Select(Asn1Sequence.GetInstance)
            .Where(x => ((DerObjectIdentifier)x.GetObjectAt(0)).Id == "1.2.840.113549.1.9.16.2.14")
            .Select(x => GetSignedData(Asn1Sequence.GetInstance(Asn1Set.GetInstance(x.GetObjectAt(1)).GetObjectAt(0))));
        return result;
    }

The TimeStampTokenHelper.GetTimeStampTokensAsSignedData helper method will extract time stamp token as SignedData structure. You may do everything you want with returned SignedData data.

Here is example how to extract signatures from SignerInfo:

var signatures = TimeStampTokenHelper.GetTimeStampTokensAsSignedData(cadesTBytes)
    .SelectMany(token => token.SignerInfos.ToArray().Select(SignerInfo.GetInstance))
    .Select(signerInfo => signerInfo.EncryptedDigest);

As final tips:

  • you can use free online ASN.1 viewer to dig into structure of your Cades T signature
  • you can use Org.BouncyCastle.Asn1.Utilities.Asn1Dump.DumpAsString method to dump string representation of Bouncycastle's ASN.1 objects

Hope this helps.

Upvotes: 2

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