private PopoPrivKey(Asn1TaggedObject obj)
        {
            this.tagNo = obj.TagNo;

            switch (tagNo)
            {
            case thisMessage:
                this.obj = DerBitString.GetInstance(obj, false);
                break;
            case subsequentMessage:
                this.obj = SubsequentMessage.ValueOf(DerInteger.GetInstance(obj, false).Value.IntValue);
                break;
            case dhMAC:
                this.obj = DerBitString.GetInstance(obj, false);
                break;
            case agreeMAC:
                this.obj = PKMacValue.GetInstance(obj, false);
                break;
            case encryptedKey:
                this.obj = EnvelopedData.GetInstance(obj, false);
                break;
            default:
                throw new ArgumentException("unknown tag in PopoPrivKey", "obj");
            }
        }

		private Evidence(Asn1TaggedObject tagged)
		{
			if (tagged.TagNo == 0)
			{
				this.tstEvidence = TimeStampTokenEvidence.GetInstance(tagged, false);
			}
		}

        private DeclarationOfMajority(
			Asn1TaggedObject o)
        {
            if (o.TagNo > 2)
                throw new ArgumentException("Bad tag number: " + o.TagNo);

            this.declaration = o;
        }

		public static RequestedCertificate GetInstance(
			Asn1TaggedObject	obj,
			bool				isExplicit)
		{
			if (!isExplicit)
				throw new ArgumentException("choice item must be explicitly tagged");

			return GetInstance(obj.GetObject());
		}

		public static DirectoryString GetInstance(
			Asn1TaggedObject	obj,
			bool				isExplicit)
		{
			if (!isExplicit)
				throw new ArgumentException("choice item must be explicitly tagged");

			return GetInstance(obj.GetObject());
		}

		/**
         * return an OriginatorIdentifierOrKey object from a tagged object.
         *
         * @param o the tagged object holding the object we want.
         * @param explicitly true if the object is meant to be explicitly
         *              tagged false otherwise.
         * @exception ArgumentException if the object held by the
         *          tagged object cannot be converted.
         */
        public static OriginatorIdentifierOrKey GetInstance(
            Asn1TaggedObject	o,
            bool				explicitly)
        {
            if (!explicitly)
            {
                throw new ArgumentException(
                        "Can't implicitly tag OriginatorIdentifierOrKey");
            }

			return GetInstance(o.GetObject());
        }

		public DistributionPointName(
            Asn1TaggedObject obj)
        {
            this.type = obj.TagNo;

			if (type == FullName)
            {
                this.name = GeneralNames.GetInstance(obj, false);
            }
            else
            {
                this.name = Asn1Set.GetInstance(obj, false);
            }
        }

		private RequestedCertificate(
			Asn1TaggedObject tagged)
		{
			switch ((Choice) tagged.TagNo)
			{
				case Choice.AttributeCertificate:
					this.attributeCert = Asn1OctetString.GetInstance(tagged, true).GetOctets();
					break;
				case Choice.PublicKeyCertificate:
					this.publicKeyCert = Asn1OctetString.GetInstance(tagged, true).GetOctets();
					break;
				default:
					throw new ArgumentException("unknown tag number: " + tagged.TagNo);
			}
		}

		/**
		 * Constructor from Asn1TaggedObject.
		 * 
		 * @param tagObj The tagged object.
		 * @throws ArgumentException if the encoding is wrong.
		 */
		private Target(
			Asn1TaggedObject tagObj)
		{
			switch ((Choice) tagObj.TagNo)
			{
				case Choice.Name:	// GeneralName is already a choice so explicit
					targetName = GeneralName.GetInstance(tagObj, true);
					break;
				case Choice.Group:
					targetGroup = GeneralName.GetInstance(tagObj, true);
					break;
				default:
					throw new ArgumentException("unknown tag: " + tagObj.TagNo);
			}
		}

		private CertOrEncCert(Asn1TaggedObject tagged)
		{
			if (tagged.TagNo == 0)
			{
				certificate = CmpCertificate.GetInstance(tagged.GetObject());
			}
			else if (tagged.TagNo == 1)
			{
				encryptedCert = EncryptedValue.GetInstance(tagged.GetObject());
			}
			else
			{
				throw new ArgumentException("unknown tag: " + tagged.TagNo, "tagged");
			}
		}

		public CertStatus(
            Asn1TaggedObject choice)
        {
            this.tagNo = choice.TagNo;

			switch (choice.TagNo)
            {
				case 1:
					value = RevokedInfo.GetInstance(choice, false);
					break;
				case 0:
				case 2:
					value = DerNull.Instance;
					break;
            }
        }

		/**
		 * Constructor for a holder for an v1 attribute certificate.
		 * 
		 * @param tagObj The ASN.1 tagged holder object.
		 */
		public Holder(
			Asn1TaggedObject tagObj)
		{
			switch (tagObj.TagNo)
			{
				case 0:
					baseCertificateID = IssuerSerial.GetInstance(tagObj, false);
					break;
				case 1:
					entityName = GeneralNames.GetInstance(tagObj, false);
					break;
				default:
					throw new ArgumentException("unknown tag in Holder");
			}

			this.version = 0;
		}

 private PkiArchiveOptions(Asn1TaggedObject tagged)
 {
     switch (tagged.TagNo)
     {
         case encryptedPrivKey:
             value = EncryptedKey.GetInstance(tagged.GetObject());
             break;
         case keyGenParameters:
             value = Asn1OctetString.GetInstance(tagged, false);
             break;
         case archiveRemGenPrivKey:
             value = DerBoolean.GetInstance(tagged, false);
             break;
         default:
             throw new ArgumentException("unknown tag number: " + tagged.TagNo, "tagged");
     }
 }

		public CertStatus(
            Asn1TaggedObject choice)
        {
            this.tagNo = choice.TagNo;

			switch (choice.TagNo)
            {
				case 1:
					value = RevokedInfo.GetInstance(choice, false);
					break;
				case 0:
				case 2:
					value = DerNull.Instance;
					break;
				default:
					throw new ArgumentException("Unknown tag encountered: " + choice.TagNo);
            }
        }

 private ProofOfPossession(Asn1TaggedObject tagged)
 {
     tagNo = tagged.TagNo;
     switch (tagNo)
     {
     case 0:
         obj = DerNull.Instance;
         break;
     case 1:
         obj = PopoSigningKey.GetInstance(tagged, false);
         break;
     case 2:
     case 3:
         obj = PopoPrivKey.GetInstance(tagged, false);
         break;
     default:
         throw new ArgumentException("unknown tag: " + tagNo, "tagged");
     }
 }

 /**
  * return a OtherRevocationInfoFormat object from a tagged object.
  *
  * @param obj the tagged object holding the object we want.
  * @param explicit true if the object is meant to be explicitly
  *              tagged false otherwise.
  * @exception IllegalArgumentException if the object held by the
  *          tagged object cannot be converted.
  */
 public static OtherRevocationInfoFormat GetInstance(Asn1TaggedObject obj, bool isExplicit)
 {
     return GetInstance(Asn1Sequence.GetInstance(obj, isExplicit));
 }

 public static Time GetInstance(
     Asn1TaggedObject	obj,
     bool				explicitly)
 {
     return GetInstance(obj.GetObject());
 }

		public static DigestInfo GetInstance(
            Asn1TaggedObject	obj,
            bool				explicitly)
        {
            return GetInstance(Asn1Sequence.GetInstance(obj, explicitly));
        }

		public static ExtendedKeyUsage GetInstance(
            Asn1TaggedObject	obj,
            bool				explicitly)
        {
            return GetInstance(Asn1Sequence.GetInstance(obj, explicitly));
        }

		public static DHValidationParms GetInstance(Asn1TaggedObject obj, bool isExplicit)
		{
			return GetInstance(Asn1Sequence.GetInstance(obj, isExplicit));
		}