README
¶
asn1
ASN.1 BER serialization Go module.
Basic Encoding Rules (BER)
BER uses a type-length-value encoding scheme. Encoded data will be structured as follows:
The Identifier octets identify the type of thing encoded. The Length octets identify the length of the thing encoded. Finally, the Content octets contain the encoded thing.
Identifier octets
The identifier octets encode the ASN.1 tag class, whether it is primitive or constructed, and tag number.
Class
The tag's class is set in bits 8 and 7 in the first octet. Possible values:
| Class | Bit 8 | Bit 7 |
|---|---|---|
| Universal | 0 | 0 |
| Application | 0 | 1 |
| Context-specific | 1 | 0 |
| Private | 1 | 1 |
Primitive/Constructed
Bit 6 sets whether the value is primitive or constructed:
| Bit 6 value | |
|---|---|
| 0 | primitive |
| 1 | constructed |
Primitive encodings represent the value directly. For instance, an INTEGER tag is primitive, and the underlying content value is an encoded integer.
Constructed encodings represent a concatenation of other encoded values.
Tag number
For tag numbers <= 30 (the universal tags), the last 5 bits are used to encode the tag number, and the identifier will be 1 octet total. For tag numbers >= 31 the last 5 bits of the first octet are encoded to 11111. The subsequent octets are then the base 128 encoding of the tag number.
Length octets
BER supports length octets in two possible forms: definite and indefinite. This module only supports the definite form.
Content Encoding
Types
| ASN.1 Type | Description | Tag | Go Types |
|---|---|---|---|
BOOLEAN |
Simple boolean value | 1 | bool |
INTEGER |
A signed integer value, with no limits | 2 | int, int8, int16, int32, int64 |
BIT STRING |
Arbitrary string of bits | 3 | |
OCTET STRING |
A value of zero or more bytes | 4 | []byte |
OBJECT IDENTIFIER |
6 | ObjectIdentifier |
|
REAL |
9 | float32, float64 |
|
Strings |
See below | See below | string |
Strings
ASN.1 has many string types:
| Type | Tag | Description |
|---|---|---|
BMPString |
30 | |
GeneralString |
27 | |
GraphicString |
25 | |
IA5String |
22 | First 128 chracters of ASCII alphabet |
NumericString |
18 | |
PrintableString |
19 | A restricted subset of ASCII alphabet |
T61String |
20 | |
UniversalString |
28 | |
UTF8String |
12 | |
VideotexString |
21 | |
VisibleString |
26 |
Explicit/Implicit Tags
ASN.1 has IMPLICIT and EXPLICIT tags.
IMPLICIT tags are derived from other types by changing the tag of the underlying type. ASN.1 notation:
[[class] number] IMPLICIT Type
***class = *** UNIVERSAL | APPLICATION | PRIVATE
Note: The IMPLICIT keyword is optional in ASN.1 modules.
If there is no class name, the tag's class is Context-specific (which can only be a component of a structured or CHOICE type).
Implicit Exaple
ASN.1 notation:
[5] IMPLICIT UTF8String
- Encode "hi"
- The identifier octet would be encoded as:
10- Context-specific defaults0- primitive101- 5
Todo
- Handle pointers
Documentation
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Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
Types ¶
type ObjectIdentifier ¶
func NewObjectIdentifier ¶
func NewObjectIdentifier(root uint8, node []uint64) (*ObjectIdentifier, error)
func (*ObjectIdentifier) ToString ¶
func (o *ObjectIdentifier) ToString() string
type Tag ¶
type Tag uint
const ( TagEndOfContent Tag = 0x00 TagBoolean Tag = 0x01 TagInteger Tag = 0x02 TagBitString Tag = 0x03 TagOctetString Tag = 0x04 TagNull Tag = 0x05 TagObjectIdentifier Tag = 0x06 TagObjectDescriptor Tag = 0x07 TagExternal Tag = 0x08 TagReal Tag = 0x09 TagEnumerated Tag = 0x0a TagEmbeddedPDV Tag = 0x0b TagUTF8String Tag = 0x0c TagRelativeOID Tag = 0x0d TagTime Tag = 0x0e TagSequence Tag = 0x10 TagSequenceOf Tag = TagSequence TagSet Tag = 0x11 TagSetOf Tag = TagSet TagNumericString Tag = 0x12 TagPrintableString Tag = 0x13 TagT61String Tag = 0x14 TagVideotexString Tag = 0x15 TagIA5String Tag = 0x16 TagUTCTime Tag = 0x17 TagGeneralizedTime Tag = 0x18 TagGraphicString Tag = 0x19 TagVisibleString Tag = 0x1a TagGeneralString Tag = 0x1b TagUniversalString Tag = 0x1c TagCharacterString Tag = 0x1d TagBMPString Tag = 0x1e )
Source Files