/// <summary>
/// Writes Identifier octet of ASN.1 object.
/// </summary>
/// <param name="asn1Class">Class of given Asn.1 object.</param>
/// <param name="tagNumber">Tag number or type of Asn.1 object.</param>
/// <param name="constructed">Constructed/Primitive bit of identifier octet.</param>
/// <returns>Encoded identifier octet of ASN.1 object.</returns>
internal static byte[] WriteTag(Asn1Class asn1Class, int tagNumber, bool constructed = false)
{
byte[] tagOctets = null;
var classPart = (int)asn1Class;
var typePart = tagNumber & 0x1F; // clear bits 8 to 6
int tag = classPart;
if (constructed)
{
tag = tag | 0x20;
}
if (asn1Class == Asn1Class.ContextSpecific && tagNumber > 30)
{
tag = tag + 31; // in long form bits 1-5 have value of 1 and tag number is encoded in the following octets
var tagValueOctets = new List <byte>();
tagValueOctets.Add((byte)tag);
DerWriterUtils.SevenBitEncode(tagNumber, tagValueOctets);
tagOctets = tagValueOctets.ToArray();
}
else
{
tag = tag + typePart;
tagOctets = new byte[1] {
(byte)tag
};
}
return(tagOctets);
}
/// <summary>
/// Calculates length of ASN.1 object
/// </summary>
/// <param name="value">Content of ASN.1 object.</param>
/// <param name="asn1Type">Type of ASN.1 object. In some types there has to be an octet before content bytes.</param>
/// <returns>Encoded length of ASN.1 object.</returns>
internal static byte[] WriteLength(IEnumerable <byte> value, Asn1Type asn1Type)
{
var length = value.Count();
if (asn1Type == Asn1Type.BitString)
{
length++; // count in the unused bits
}
byte[] lengthOctets = DerWriterUtils.EncodeLength(length);
return(lengthOctets);
}
