Examples

Dump

This command line utility reads a X509.v3 certificate (in DER or PEM encoding), decodes it and outputs a textual representation. It more or less mimics openssl asn1parse:

$ python examples/dump.py examples/test.crt

[U] SEQUENCE
  [U] SEQUENCE
    [C] 0x0
      [U] INTEGER: 2
    [U] INTEGER: 5424
    [U] SEQUENCE
      [U] OBJECT: 1.2.840.113549.1.1.5
      [U] NULL: None
    [U] SEQUENCE
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.6
          [U] PRINTABLESTRING: --
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.8
          [U] PRINTABLESTRING: SomeState
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.7
          [U] PRINTABLESTRING: SomeCity
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.10
          [U] PRINTABLESTRING: SomeOrganization
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.11
          [U] PRINTABLESTRING: SomeOrganizationalUnit
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.3
          [U] PRINTABLESTRING: localhost.localdomain
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 1.2.840.113549.1.9.1
          [U] IA5STRING: root@localhost.localdomain
    [U] SEQUENCE
      [U] UTCTIME: 080205092331Z
      [U] UTCTIME: 090204092331Z
    [U] SEQUENCE
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.6
          [U] PRINTABLESTRING: --
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.8
          [U] PRINTABLESTRING: SomeState
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.7
          [U] PRINTABLESTRING: SomeCity
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.10
          [U] PRINTABLESTRING: SomeOrganization
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.11
          [U] PRINTABLESTRING: SomeOrganizationalUnit
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 2.5.4.3
          [U] PRINTABLESTRING: localhost.localdomain
      [U] SET
        [U] SEQUENCE
          [U] OBJECT: 1.2.840.113549.1.9.1
          [U] IA5STRING: root@localhost.localdomain
    [U] SEQUENCE
      [U] SEQUENCE
        [U] OBJECT: 1.2.840.113549.1.1.1
        [U] NULL: None
      [U] BIT STRING: 0xb'0030818902818100D51...10610203010001'
    [C] BIT STRING
      [U] SEQUENCE
        [U] SEQUENCE
          [U] OBJECT: 2.5.29.14
          [U] OCTET STRING: 0xb'04140A4BFA8754177E30B4217156510FD291C3300236'
        [U] SEQUENCE
          [U] OBJECT: 2.5.29.35
          [U] OCTET STRING: 0xb'3081DE80140A4...D61696E82021530'
        [U] SEQUENCE
          [U] OBJECT: 2.5.29.19
          [U] OCTET STRING: 0xb'30030101FF'
  [U] SEQUENCE
    [U] OBJECT: 1.2.840.113549.1.1.5
    [U] NULL: None
  [U] BIT STRING: 0xb'004E124658A357C59AABFA3...8A6245C7FC58B45A'

The main function is pretty_print:

 1def pretty_print(input_stream, output_stream, indent=0):
 2     """Pretty print ASN.1 data."""
 3     while not input_stream.eof():
 4         tag = input_stream.peek()
 5         if tag.typ == asn1.Types.Primitive:
 6             tag, value = input_stream.read()
 7             output_stream.write(' ' * indent)
 8             output_stream.write('[{}] {}: {}\n'.format(class_id_to_string(tag.cls),
 9                 tag_id_to_string(tag.nr), value_to_string(tag.nr, value)))
10         elif tag.typ == asn1.Types.Constructed:
11             output_stream.write(' ' * indent)
12             output_stream.write('[{}] {}\n'.format(class_id_to_string(tag.cls),
13                 tag_id_to_string(tag.nr)))
14             input_stream.enter()
15             pretty_print(input_stream, output_stream, indent + 2)
16             input_stream.leave()

This code:

  • line 3: Loops until its reaches the end of the input stream (with Decoder.eof()).

  • line 4: Looks (with Decoder.peek()) at the current tag.

  • line 5: If the tag is primitive (TypePrimitive) …

  • line 6: … the code reads (with Decoder.read()) the current tag.

  • line 8: Then it displays its number and value (after some mapping to be more user-fiendly).

  • line 10: If the tag is constructed (TypeConstructed) …

  • line 12: … the code displays its class and number.

  • line 14: Then it enters inside the tag and …

  • line 15: … calls itself recursively to decode the ASN.1 tags inside.

  • line 16: Leaves the current constructed tag (with Decoder.leave()) to continue the decoding of its siblings.