Encoded Tag Bytes

The Tag field in a TLV triplet identifies the type of the data structure being sent between computers. For example, the tag for an integer is 0x02, and the tag for an object identifier is 0x06. Although multiple bytes are permitted, none of the data types used by the Certificate Enrollment API require more than one. The following illustration shows the breakdown of a Tag value. Bits 7 and 6 identify the ASN.1 tagging class. There are four available classes, but the Certificate Enrollment API uses data types that belong only to the UNIVERSAL class. Bit 5 identifies whether the encoding form is primitive or constructed. Basic and string types are encoded by using primitive forms, constructed types by using a constructed form. For more information, see ASN.1 Type System. Bits 4 through 0 contain the tag number.

The following table lists the data types supported by the Certificate Enrollment API, the encoding form used, and the tag value.

Type	ASN.1 class	Encoding form	Tag value
BIT STRING	UNIVERSAL	Primitive	00000011 (0x03)
BOOLEAN	UNIVERSAL	Primitive	00000001 (0x01)
INTEGER	UNIVERSAL	Primitive	00000010 (0x02)
NULL	UNIVERSAL	Primitive	00000101 (0x05)
OBJECT IDENTIFIER	UNIVERSAL	Primitive	00000110 (0x06)
OCTET STRING	UNIVERSAL	Primitive	00000100 (0x04)
BMPString	UNIVERSAL	Primitive	00011110 (0x1E)
IA5String	UNIVERSAL	Primitive	00010110 (0x16)
PrintableString	UNIVERSAL	Primitive	00010011 (0x13)
TeletexString	UNIVERSAL	Primitive	00010100 (0x14)
UTF8String	UNIVERSAL	Primitive	00001100 (0x0C)
SEQUENCE	UNIVERSAL	Constructed	00110000 (0x30)
SEQUENCE OF	UNIVERSAL	Constructed	00110000 (0x30)
SET	UNIVERSAL	Constructed	00110001 (0x31)
SET OF	UNIVERSAL	Constructed	00110001 (0x31)

Related topics

DER Transfer Syntax

Encoded Length and Value Bytes