How to parse the ASN1 data by using bouncycastle

Question

I have the byte array which is in the form of asn1 format..now i want to parse this data to get required information..Here is the code they have written for c++..now i want to do the same in java.could any one help on this.

ASN1 asn1(in);

 int startPos = in.tellg();
 asn1.enterObject(asn1.getTag());
 int endPos = asn1.getCurrentLength() + in.tellg();

 ubytearray acctId, valData;

 while (in.tellg() < endPos) {
     asn1.enterObject(0x30); //0x30 TAG_SEQ

     // read the name
     ubytearray nameData = asn1.getContent(ASN1_TAG_UTF8_STRING);
     ubytearray octstr =  asn1.getContent(ASN1_TAG_OCTET_STRING);

ASN1 asn2(octstr); asn2.enterObject(0x30); ustring urlstr(asn2.getContent(ASN1_TAG_UTF8_STRING)); ustring nameStr(asn2.getContent(ASN1_TAG_UTF8_STRING)); asn2.enterObject(0x30); ubytearray certs = asn2.getContent(ASN1_TAG_OCTET_STRING);

     if ((urlstr.length() > 0)  && (nameStr.length() > 0) && (certs.length() > 0)) {
         printf("url %s\n", urlstr.c_str());
         printf("name %s\n", nameStr.c_str());
         printf("certs len:%d\n", certs.length());  

} }

Answer 1

You should be able to use the classes in org.bouncycastle.asn1, beginning with ASN1InputStream, to read the ASN.1 structure from an InputStream or byte[]. It's a little bit difficult to follow your example code, but something like this might help you get started:

    byte[] data = null; // obviously need to supply real data here
    ASN1InputStream input = new ASN1InputStream(data);

    ASN1Primitive p;
    while ((p = input.readObject()) != null) {
        ASN1Sequence asn1 = ASN1Sequence.getInstance(p);

        DERUTF8String nameData = DERUTF8String.getInstance(asn1.getObjectAt(0));
        ASN1OctetString octstr = ASN1OctetString.getInstance(asn1.getObjectAt(1));

        ASN1Sequence asn2 = ASN1Sequence.getInstance(ASN1Primitive.fromByteArray(octstr.getOctets()));

        // ... and so on
    }

If you find the structure of the data hard to understand, perhaps the org.bouncycastle.asn1.util.ASN1Dump class will be helpful:

    byte[] data = null; // obviously need to supply real data here
    ASN1InputStream input = new ASN1InputStream(data);

    ASN1Primitive p;
    while ((p = input.readObject()) != null) {
        System.out.println(ASN1Dump.dumpAsString(p));
    }