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I have been doing this task for more than 3 days, and finally I realised that I need some help. I have 2 files - a PKCS#7 file(base64 encoded) and a file which was signed by the PKCS#7(say, pdf). My question is how can I check whether the sign is right or not and the file is intact. I ended up with this algorithm:

  1. Transform a pdf file to base64
  2. Check all the certificates in PKCS#7(whether some is out of date, or not valid)
  3. Get a hash from a pdf file(applying a specific hash algorithm)
  4. Get a hash from a PKCS#7 file(applying the same algorithm)
  5. Finally check these 2 hashs

I hope it's the right order and with it's help I can perform my task and finally check integrity. But I don't know how to perform it using Java. The library I supposed to use is Bouncy Castle. Before it, I just processed the PKCS#7 file like this:

String rawString = ASN1ObjectIdentifier.fromByteArray(bytesArray).toString();

String rawStringForSurname = rawString.substring(rawString.indexOf("2.5.4.4,") + 9, rawString.length());
String signSurname = rawStringForSurname.substring(0, rawStringForSurname.indexOf("]"));

String rawStringForGivenName = rawString.substring(rawString.indexOf("2.5.4.42,") + 10, rawString.length());
String signGivenName = rawStringForGivenName.substring(0, rawStringForGivenName.indexOf("]"));

I guess this approach is awful. Getting a String from the whole raw ASN.1 is a terrible idea, though it's the only solution I did by myself. And using this approach I can not somehow "compare" the pdf and the PKCS#7 somehow. How can I perform it using X509Cerftificate, SignedData and other feautures from Bouncy Castle? Please correct me if I wrong about the order of actions and the actions itself.

Колян
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  • PDF signing is a special case since the PDF format supports siging within the Format. Both PDF content to be signed and the signature(s) are contained in PDF. [This Library](https://pdfbox.apache.org/) will help you with the PDF Format. If you can start with siging a text file, this is much simpler. – hengsti Nov 17 '17 at 11:00
  • [This Question](https://stackoverflow.com/questions/13565515/java-signing-files-with-bouncycastle-create-signature-of-a-file-using-secret-k) shows better approach using Bouncy Castle – hengsti Nov 17 '17 at 11:07

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