CMSAuthenticatedDataParser.getUnauthAttrs() always returns null, and AuthenticatedDataParser.getUnauthAttrs() throws ClassCastException #2532

Summary

CMSAuthenticatedDataParser.getUnauthAttrs() never returns the unauthenticated attributes of an AuthenticatedData. It always returns null. Behind that is a second defect: once the first is fixed, the call throws ClassCastException instead.

Both are present in 1.86 and on main (d401e82d3f). The non-streaming CMSAuthenticatedData.getUnauthAttrs() reads the same message correctly.

Defect 1: unauthAttrNotRead is never set

CMSAuthenticatedDataParser.getUnauthAttrs() only reads the attributes if (unauthAttrs == null && unauthAttrNotRead). The constructor sets authAttrNotRead = true but never sets unauthAttrNotRead, so the guard is always false and the method returns null.

CMSAuthEnvelopedDataParser sets both flags in its constructor:

authAttrNotRead = true;
unauthAttrNotRead = true;

Defect 2: ClassCastException in AuthenticatedDataParser.getUnauthAttrs()

ASN1TaggedObject o = (ASN1TaggedObject)nextObject;

nextObject comes from an ASN1SequenceParser, so it is a DLTaggedObjectParser or BERTaggedObjectParser, never an ASN1TaggedObject. The sibling AuthEnvelopedDataParser.getUnauthAttrs() casts to ASN1TaggedObjectParser, which is correct.

Defect 1 hides defect 2 in the cms API. Calling org.bouncycastle.asn1.cms.AuthenticatedDataParser directly hits defect 2 on any message that has unauthAttrs.

Reproducer

The message is generated by BC itself:

Security.addProvider(new BouncyCastleProvider());

CMSAuthenticatedDataGenerator gen = new CMSAuthenticatedDataGenerator();
gen.addRecipientInfoGenerator(new JcePasswordRecipientInfoGenerator(
    CMSAlgorithm.AES128_CBC, "password".toCharArray()).setProvider("BC")
    .setPasswordConversionScheme(0).setSaltAndIterationCount(new byte[20], 1000));
Attribute attr = new Attribute(new ASN1ObjectIdentifier("1.2.3.4"),
    new DERSet(new DERUTF8String("x")));
gen.setUnauthenticatedAttributeGenerator(
    new SimpleAttributeTableGenerator(new AttributeTable(attr)));
byte[] encoded = gen.generate(new CMSProcessableByteArray("hello".getBytes("UTF-8")),
    new JceCMSMacCalculatorBuilder(CMSAlgorithm.DES_EDE3_CBC).setProvider("BC").build())
    .getEncoded();

// non-streaming: 1 attribute
System.out.println(new CMSAuthenticatedData(encoded).getUnauthAttrs().size());

// streaming, read in the documented order: content, mac, attributes
CMSAuthenticatedDataParser parser = new CMSAuthenticatedDataParser(encoded);
RecipientInformation recipient =
    (RecipientInformation)parser.getRecipientInfos().getRecipients().iterator().next();
Streams.drain(recipient.getContentStream(
    new JcePasswordAuthenticatedRecipient("password".toCharArray()).setProvider("BC")
        .setPasswordConversionScheme(0)).getContentStream());
System.out.println(Arrays.areEqual(parser.getMac(), recipient.getMac()));   // true
System.out.println(parser.getUnauthAttrs());                                // null

If unauthAttrNotRead is set to true (via reflection, to simulate fixing defect 1), the last call throws:

java.lang.ClassCastException: class org.bouncycastle.asn1.DLTaggedObjectParser cannot be cast to class org.bouncycastle.asn1.ASN1TaggedObject
    at org.bouncycastle.asn1.cms.AuthenticatedDataParser.getUnauthAttrs
    at org.bouncycastle.cms.CMSAuthenticatedDataParser.getUnauthAttrs

Suggested fix

1. In the CMSAuthenticatedDataParser constructor, set this.unauthAttrNotRead = true; next to authAttrNotRead.
2. In AuthenticatedDataParser.getUnauthAttrs(), cast to ASN1TaggedObjectParser, as AuthEnvelopedDataParser does.
3. Add a test that reads unauthenticated attributes through CMSAuthenticatedDataParser. No existing test does: NewAuthenticatedDataStreamTest never calls getUnauthAttrs(), which is how both defects went unnoticed.