Documentation

Overview

    Package asn1 implements parsing of DER-encoded ASN.1 data structures, as defined in ITU-T Rec X.690.

    See also “A Layman's Guide to a Subset of ASN.1, BER, and DER,” http://luca.ntop.org/Teaching/Appunti/asn1.html.

    Index

    Constants

    View Source
    const (
    	TagBoolean         = 1
    	TagInteger         = 2
    	TagBitString       = 3
    	TagOctetString     = 4
    	TagNull            = 5
    	TagOID             = 6
    	TagEnum            = 10
    	TagUTF8String      = 12
    	TagSequence        = 16
    	TagSet             = 17
    	TagNumericString   = 18
    	TagPrintableString = 19
    	TagT61String       = 20
    	TagIA5String       = 22
    	TagUTCTime         = 23
    	TagGeneralizedTime = 24
    	TagGeneralString   = 27
    	TagBMPString       = 30
    )

      ASN.1 tags represent the type of the following object.

      View Source
      const (
      	ClassUniversal       = 0
      	ClassApplication     = 1
      	ClassContextSpecific = 2
      	ClassPrivate         = 3
      )

        ASN.1 class types represent the namespace of the tag.

        Variables

        View Source
        var NullBytes = []byte{TagNull, 0}

          NullBytes contains bytes representing the DER-encoded ASN.1 NULL type.

          View Source
          var NullRawValue = RawValue{Tag: TagNull}

            NullRawValue is a RawValue with its Tag set to the ASN.1 NULL type tag (5).

            Functions

            func Marshal

            func Marshal(val interface{}) ([]byte, error)

              Marshal returns the ASN.1 encoding of val.

              In addition to the struct tags recognised by Unmarshal, the following can be used:

              ia5:         causes strings to be marshaled as ASN.1, IA5String values
              omitempty:   causes empty slices to be skipped
              printable:   causes strings to be marshaled as ASN.1, PrintableString values
              utf8:        causes strings to be marshaled as ASN.1, UTF8String values
              utc:         causes time.Time to be marshaled as ASN.1, UTCTime values
              generalized: causes time.Time to be marshaled as ASN.1, GeneralizedTime values
              

              func MarshalWithParams

              func MarshalWithParams(val interface{}, params string) ([]byte, error)

                MarshalWithParams allows field parameters to be specified for the top-level element. The form of the params is the same as the field tags.

                func Unmarshal

                func Unmarshal(b []byte, val interface{}) (rest []byte, err error)

                  Unmarshal parses the DER-encoded ASN.1 data structure b and uses the reflect package to fill in an arbitrary value pointed at by val. Because Unmarshal uses the reflect package, the structs being written to must use upper case field names. If val is nil or not a pointer, Unmarshal returns an error.

                  After parsing b, any bytes that were leftover and not used to fill val will be returned in rest. When parsing a SEQUENCE into a struct, any trailing elements of the SEQUENCE that do not have matching fields in val will not be included in rest, as these are considered valid elements of the SEQUENCE and not trailing data.

                  An ASN.1 INTEGER can be written to an int, int32, int64, or *big.Int (from the math/big package). If the encoded value does not fit in the Go type, Unmarshal returns a parse error.

                  An ASN.1 BIT STRING can be written to a BitString.

                  An ASN.1 OCTET STRING can be written to a []byte.

                  An ASN.1 OBJECT IDENTIFIER can be written to an ObjectIdentifier.

                  An ASN.1 ENUMERATED can be written to an Enumerated.

                  An ASN.1 UTCTIME or GENERALIZEDTIME can be written to a time.Time.

                  An ASN.1 PrintableString, IA5String, or NumericString can be written to a string.

                  Any of the above ASN.1 values can be written to an interface{}. The value stored in the interface has the corresponding Go type. For integers, that type is int64.

                  An ASN.1 SEQUENCE OF x or SET OF x can be written to a slice if an x can be written to the slice's element type.

                  An ASN.1 SEQUENCE or SET can be written to a struct if each of the elements in the sequence can be written to the corresponding element in the struct.

                  The following tags on struct fields have special meaning to Unmarshal:

                  application specifies that an APPLICATION tag is used
                  private     specifies that a PRIVATE tag is used
                  default:x   sets the default value for optional integer fields (only used if optional is also present)
                  explicit    specifies that an additional, explicit tag wraps the implicit one
                  optional    marks the field as ASN.1 OPTIONAL
                  set         causes a SET, rather than a SEQUENCE type to be expected
                  tag:x       specifies the ASN.1 tag number; implies ASN.1 CONTEXT SPECIFIC
                  

                  When decoding an ASN.1 value with an IMPLICIT tag into a string field, Unmarshal will default to a PrintableString, which doesn't support characters such as '@' and '&'. To force other encodings, use the following tags:

                  ia5     causes strings to be unmarshaled as ASN.1 IA5String values
                  numeric causes strings to be unmarshaled as ASN.1 NumericString values
                  utf8    causes strings to be unmarshaled as ASN.1 UTF8String values
                  

                  If the type of the first field of a structure is RawContent then the raw ASN1 contents of the struct will be stored in it.

                  If the name of a slice type ends with "SET" then it's treated as if the "set" tag was set on it. This results in interpreting the type as a SET OF x rather than a SEQUENCE OF x. This can be used with nested slices where a struct tag cannot be given.

                  Other ASN.1 types are not supported; if it encounters them, Unmarshal returns a parse error.

                  func UnmarshalWithParams

                  func UnmarshalWithParams(b []byte, val interface{}, params string) (rest []byte, err error)

                    UnmarshalWithParams allows field parameters to be specified for the top-level element. The form of the params is the same as the field tags.

                    Types

                    type BitString

                    type BitString struct {
                    	Bytes     []byte // bits packed into bytes.
                    	BitLength int    // length in bits.
                    }

                      BitString is the structure to use when you want an ASN.1 BIT STRING type. A bit string is padded up to the nearest byte in memory and the number of valid bits is recorded. Padding bits will be zero.

                      func (BitString) At

                      func (b BitString) At(i int) int

                        At returns the bit at the given index. If the index is out of range it returns false.

                        func (BitString) RightAlign

                        func (b BitString) RightAlign() []byte

                          RightAlign returns a slice where the padding bits are at the beginning. The slice may share memory with the BitString.

                          type Enumerated

                          type Enumerated int

                            An Enumerated is represented as a plain int.

                            type Flag

                            type Flag bool

                              A Flag accepts any data and is set to true if present.

                              type ObjectIdentifier

                              type ObjectIdentifier []int

                                An ObjectIdentifier represents an ASN.1 OBJECT IDENTIFIER.

                                func (ObjectIdentifier) Equal

                                func (oi ObjectIdentifier) Equal(other ObjectIdentifier) bool

                                  Equal reports whether oi and other represent the same identifier.

                                  func (ObjectIdentifier) String

                                  func (oi ObjectIdentifier) String() string

                                  type RawContent

                                  type RawContent []byte

                                    RawContent is used to signal that the undecoded, DER data needs to be preserved for a struct. To use it, the first field of the struct must have this type. It's an error for any of the other fields to have this type.

                                    type RawValue

                                    type RawValue struct {
                                    	Class, Tag int
                                    	IsCompound bool
                                    	Bytes      []byte
                                    	FullBytes  []byte // includes the tag and length
                                    }

                                      A RawValue represents an undecoded ASN.1 object.

                                      type StructuralError

                                      type StructuralError struct {
                                      	Msg string
                                      }

                                        A StructuralError suggests that the ASN.1 data is valid, but the Go type which is receiving it doesn't match.

                                        func (StructuralError) Error

                                        func (e StructuralError) Error() string

                                        type SyntaxError

                                        type SyntaxError struct {
                                        	Msg string
                                        }

                                          A SyntaxError suggests that the ASN.1 data is invalid.

                                          func (SyntaxError) Error

                                          func (e SyntaxError) Error() string