/// <summary>
/// Given a CBOR tree, decode and return the correct COSE message object.
/// Message type can be provided explicitly or inferred from the CBOR tag element.
/// If the explicit and inferred elements provide different answers, then it fails.
/// </summary>
/// <param name="messageObject"></param>
/// <param name="defaultTag"></param>
/// <returns></returns>
public static Message DecodeFromCBOR(CBORObject messageObject, Tags defaultTag = Tags.Unknown)
{
if (messageObject.Type != CBORType.Array)
{
throw new CoseException("Message is not a COSE security message.");
}
if (messageObject.IsTagged)
{
if (messageObject.GetAllTags().Count() != 1)
{
throw new CoseException("Malformed message - too many tags");
}
if (defaultTag == Tags.Unknown)
{
defaultTag = (Tags)messageObject.MostOuterTag.ToInt32Checked();
}
else if (defaultTag != (Tags)messageObject.MostOuterTag.ToInt32Checked())
{
throw new CoseException("Passed in tag does not match actual tag");
}
}
Message returnObject;
switch (defaultTag)
{
case Tags.Unknown:
throw new CoseException("Message was not tagged and no default tagging option given");
case Tags.Signed:
SignMessage sig = new SignMessage();
sig.InternalDecodeFromCBORObject(messageObject);
returnObject = sig;
break;
case Tags.Sign1:
Sign1Message sig0 = new Sign1Message();
sig0.InternalDecodeFromCBORObject(messageObject);
returnObject = sig0;
break;
case Tags.MAC:
MACMessage mac = new MACMessage();
mac.InternalDecodeFromCBORObject(messageObject);
returnObject = mac;
break;
case Tags.MAC0:
MAC0Message mac0 = new MAC0Message();
mac0.InternalDecodeFromCBORObject(messageObject);
returnObject = mac0;
break;
case Tags.Encrypt: // It is an encrytion message
EncryptMessage enc = new EncryptMessage();
enc.InternalDecodeFromCBORObject(messageObject);
returnObject = enc;
break;
case Tags.Encrypt0:
Encrypt0Message enc0 = new Encrypt0Message();
enc0.InternalDecodeFromCBORObject(messageObject);
returnObject = enc0;
break;
default:
throw new CoseException("Message is not recognized as a COSE security message.");
}
// Check for counter signatures
CBORObject csig = returnObject.FindAttribute(HeaderKeys.CounterSignature, UNPROTECTED);
if (csig != null)
{
if (csig.Type != CBORType.Array || csig.Count == 0)
{
throw new CoseException("Invalid counter signature attribute");
}
if (csig[0].Type == CBORType.Array)
{
foreach (CBORObject cbor in csig.Values)
{
if (cbor.Type != CBORType.Array)
{
throw new CoseException("Invalid Counter signature attribute");
}
CounterSignature cs = new CounterSignature(cbor);
cs.SetObject(returnObject);
returnObject.CounterSignerList.Add(cs);
}
}
else
{
CounterSignature cs = new CounterSignature(csig);
cs.SetObject(returnObject);
returnObject.CounterSignerList.Add(cs);
}
}
csig = returnObject.FindAttribute(HeaderKeys.CounterSignature0, UNPROTECTED);
if (csig != null)
{
if (csig.Type != CBORType.ByteString)
{
throw new CoseException("Invalid CounterSignature0 attribute");
}
CounterSignature1 cs = new CounterSignature1(csig.GetByteString());
cs.SetObject(returnObject);
returnObject.CounterSigner1 = cs;
}
return(returnObject);
}