ASN.1 DER (Abstract Syntax Notation One, Distinguished Encoding Rules): C++/STL parsing library

ASN.1 (Abstract Syntax Notation One) DER (Distinguished Encoding Rules) is a standard-backed serialization scheme used in many different use-cases. Particularly popular usage scenarios are X.509 certificates and some telecommunication / networking protocols.

DER is self-describing encoding scheme which allows representation of simple, atomic data elements, such as strings and numbers, and complex objects, such as sequences of other elements.

DER is a subset of BER (Basic Encoding Rules), with an emphasis on being non-ambiguous: there's always exactly one canonical way to encode a data structure defined in terms of ASN.1 using DER.

This spec allows full parsing of format syntax, but to understand the semantics, one would typically require a dictionary of Object Identifiers (OIDs), to match OID bodies against some human-readable list of constants. OIDs are covered by many different standards, so typically it's simpler to use a pre-compiled list of them, such as:

  • https://www.cs.auckland.ac.nz/~pgut001/dumpasn1.cfg
  • http://oid-info.com/
  • https://www.alvestrand.no/objectid/top.html

KS implementation details

License: CC0-1.0

This page hosts a formal specification of ASN.1 DER (Abstract Syntax Notation One, Distinguished Encoding Rules) using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.

Usage

Using Kaitai Struct in C++/STL usually consists of 3 steps.

  1. We need to create an STL input stream (std::istream).
    • One can open a stream for reading from a local file:
      #include <fstream>
      
      std::ifstream is("path/to/local/file.asn1_der", std::ifstream::binary);
    • Or one can prepare a stream for reading from existing std::string str:
      #include <sstream>
      
      std::istringstream is(str);
    • Or one can parse arbitrary char* buffer in memory, given that we know its size:
      #include <sstream>
      
      const char buf[] = { ... };
      std::string str(buf, sizeof buf);
      std::istringstream is(str);
  2. We need to wrap our input stream into Kaitai stream:
    #include <kaitai/kaitaistream.h>
    
    kaitai::kstream ks(&is);
  3. And finally, we can invoke the parsing:
    asn1_der_t data(&ks);

After that, one can get various attributes from the structure by invoking getter methods like:

data.type_tag() // => get type tag

C++/STL source code to parse ASN.1 DER (Abstract Syntax Notation One, Distinguished Encoding Rules)

asn1_der.h

#ifndef ASN1_DER_H_
#define ASN1_DER_H_

// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

#include "kaitai/kaitaistruct.h"

#include <stdint.h>
#include <vector>

#if KAITAI_STRUCT_VERSION < 7000L
#error "Incompatible Kaitai Struct C++/STL API: version 0.7 or later is required"
#endif

/**
 * ASN.1 (Abstract Syntax Notation One) DER (Distinguished Encoding
 * Rules) is a standard-backed serialization scheme used in many
 * different use-cases. Particularly popular usage scenarios are X.509
 * certificates and some telecommunication / networking protocols.
 * 
 * DER is self-describing encoding scheme which allows representation
 * of simple, atomic data elements, such as strings and numbers, and
 * complex objects, such as sequences of other elements.
 * 
 * DER is a subset of BER (Basic Encoding Rules), with an emphasis on
 * being non-ambiguous: there's always exactly one canonical way to
 * encode a data structure defined in terms of ASN.1 using DER.
 * 
 * This spec allows full parsing of format syntax, but to understand
 * the semantics, one would typically require a dictionary of Object
 * Identifiers (OIDs), to match OID bodies against some human-readable
 * list of constants. OIDs are covered by many different standards,
 * so typically it's simpler to use a pre-compiled list of them, such
 * as:
 * 
 * * https://www.cs.auckland.ac.nz/~pgut001/dumpasn1.cfg
 * * http://oid-info.com/
 * * https://www.alvestrand.no/objectid/top.html
 * \sa Source
 */

class asn1_der_t : public kaitai::kstruct {

public:
    class body_sequence_t;
    class body_utf8string_t;
    class body_object_id_t;
    class len_encoded_t;
    class body_printable_string_t;

    enum type_tag_t {
        TYPE_TAG_END_OF_CONTENT = 0,
        TYPE_TAG_BOOLEAN = 1,
        TYPE_TAG_INTEGER = 2,
        TYPE_TAG_BIT_STRING = 3,
        TYPE_TAG_OCTET_STRING = 4,
        TYPE_TAG_NULL_VALUE = 5,
        TYPE_TAG_OBJECT_ID = 6,
        TYPE_TAG_OBJECT_DESCRIPTOR = 7,
        TYPE_TAG_EXTERNAL = 8,
        TYPE_TAG_REAL = 9,
        TYPE_TAG_ENUMERATED = 10,
        TYPE_TAG_EMBEDDED_PDV = 11,
        TYPE_TAG_UTF8STRING = 12,
        TYPE_TAG_RELATIVE_OID = 13,
        TYPE_TAG_SEQUENCE_10 = 16,
        TYPE_TAG_PRINTABLE_STRING = 19,
        TYPE_TAG_IA5STRING = 22,
        TYPE_TAG_SEQUENCE_30 = 48,
        TYPE_TAG_SET = 49
    };

    asn1_der_t(kaitai::kstream* p__io, kaitai::kstruct* p__parent = 0, asn1_der_t* p__root = 0);

private:
    void _read();

public:
    ~asn1_der_t();

    class body_sequence_t : public kaitai::kstruct {

    public:

        body_sequence_t(kaitai::kstream* p__io, asn1_der_t* p__parent = 0, asn1_der_t* p__root = 0);

    private:
        void _read();

    public:
        ~body_sequence_t();

    private:
        std::vector<asn1_der_t*>* m_entries;
        asn1_der_t* m__root;
        asn1_der_t* m__parent;

    public:
        std::vector<asn1_der_t*>* entries() const { return m_entries; }
        asn1_der_t* _root() const { return m__root; }
        asn1_der_t* _parent() const { return m__parent; }
    };

    class body_utf8string_t : public kaitai::kstruct {

    public:

        body_utf8string_t(kaitai::kstream* p__io, asn1_der_t* p__parent = 0, asn1_der_t* p__root = 0);

    private:
        void _read();

    public:
        ~body_utf8string_t();

    private:
        std::string m_str;
        asn1_der_t* m__root;
        asn1_der_t* m__parent;

    public:
        std::string str() const { return m_str; }
        asn1_der_t* _root() const { return m__root; }
        asn1_der_t* _parent() const { return m__parent; }
    };

    /**
     * \sa Source
     */

    class body_object_id_t : public kaitai::kstruct {

    public:

        body_object_id_t(kaitai::kstream* p__io, asn1_der_t* p__parent = 0, asn1_der_t* p__root = 0);

    private:
        void _read();

    public:
        ~body_object_id_t();

    private:
        bool f_first;
        int32_t m_first;

    public:
        int32_t first();

    private:
        bool f_second;
        int32_t m_second;

    public:
        int32_t second();

    private:
        uint8_t m_first_and_second;
        std::string m_rest;
        asn1_der_t* m__root;
        asn1_der_t* m__parent;

    public:
        uint8_t first_and_second() const { return m_first_and_second; }
        std::string rest() const { return m_rest; }
        asn1_der_t* _root() const { return m__root; }
        asn1_der_t* _parent() const { return m__parent; }
    };

    class len_encoded_t : public kaitai::kstruct {

    public:

        len_encoded_t(kaitai::kstream* p__io, asn1_der_t* p__parent = 0, asn1_der_t* p__root = 0);

    private:
        void _read();

    public:
        ~len_encoded_t();

    private:
        bool f_result;
        uint16_t m_result;

    public:
        uint16_t result();

    private:
        uint8_t m_b1;
        uint16_t m_int2;
        bool n_int2;

    public:
        bool _is_null_int2() { int2(); return n_int2; };

    private:
        asn1_der_t* m__root;
        asn1_der_t* m__parent;

    public:
        uint8_t b1() const { return m_b1; }
        uint16_t int2() const { return m_int2; }
        asn1_der_t* _root() const { return m__root; }
        asn1_der_t* _parent() const { return m__parent; }
    };

    class body_printable_string_t : public kaitai::kstruct {

    public:

        body_printable_string_t(kaitai::kstream* p__io, asn1_der_t* p__parent = 0, asn1_der_t* p__root = 0);

    private:
        void _read();

    public:
        ~body_printable_string_t();

    private:
        std::string m_str;
        asn1_der_t* m__root;
        asn1_der_t* m__parent;

    public:
        std::string str() const { return m_str; }
        asn1_der_t* _root() const { return m__root; }
        asn1_der_t* _parent() const { return m__parent; }
    };

private:
    type_tag_t m_type_tag;
    len_encoded_t* m_len;
    kaitai::kstruct* m_body;
    bool n_body;

public:
    bool _is_null_body() { body(); return n_body; };

private:
    asn1_der_t* m__root;
    kaitai::kstruct* m__parent;
    std::string m__raw_body;
    kaitai::kstream* m__io__raw_body;

public:
    type_tag_t type_tag() const { return m_type_tag; }
    len_encoded_t* len() const { return m_len; }
    kaitai::kstruct* body() const { return m_body; }
    asn1_der_t* _root() const { return m__root; }
    kaitai::kstruct* _parent() const { return m__parent; }
    std::string _raw_body() const { return m__raw_body; }
    kaitai::kstream* _io__raw_body() const { return m__io__raw_body; }
};

#endif  // ASN1_DER_H_

asn1_der.cpp

// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild

#include "asn1_der.h"



asn1_der_t::asn1_der_t(kaitai::kstream* p__io, kaitai::kstruct* p__parent, asn1_der_t* p__root) : kaitai::kstruct(p__io) {
    m__parent = p__parent;
    m__root = this;
    _read();
}

void asn1_der_t::_read() {
    m_type_tag = static_cast<asn1_der_t::type_tag_t>(m__io->read_u1());
    m_len = new len_encoded_t(m__io, this, m__root);
    n_body = true;
    switch (type_tag()) {
    case TYPE_TAG_SEQUENCE_30: {
        n_body = false;
        m__raw_body = m__io->read_bytes(len()->result());
        m__io__raw_body = new kaitai::kstream(m__raw_body);
        m_body = new body_sequence_t(m__io__raw_body, this, m__root);
        break;
    }
    case TYPE_TAG_SEQUENCE_10: {
        n_body = false;
        m__raw_body = m__io->read_bytes(len()->result());
        m__io__raw_body = new kaitai::kstream(m__raw_body);
        m_body = new body_sequence_t(m__io__raw_body, this, m__root);
        break;
    }
    case TYPE_TAG_UTF8STRING: {
        n_body = false;
        m__raw_body = m__io->read_bytes(len()->result());
        m__io__raw_body = new kaitai::kstream(m__raw_body);
        m_body = new body_utf8string_t(m__io__raw_body, this, m__root);
        break;
    }
    case TYPE_TAG_PRINTABLE_STRING: {
        n_body = false;
        m__raw_body = m__io->read_bytes(len()->result());
        m__io__raw_body = new kaitai::kstream(m__raw_body);
        m_body = new body_printable_string_t(m__io__raw_body, this, m__root);
        break;
    }
    case TYPE_TAG_OBJECT_ID: {
        n_body = false;
        m__raw_body = m__io->read_bytes(len()->result());
        m__io__raw_body = new kaitai::kstream(m__raw_body);
        m_body = new body_object_id_t(m__io__raw_body, this, m__root);
        break;
    }
    case TYPE_TAG_SET: {
        n_body = false;
        m__raw_body = m__io->read_bytes(len()->result());
        m__io__raw_body = new kaitai::kstream(m__raw_body);
        m_body = new body_sequence_t(m__io__raw_body, this, m__root);
        break;
    }
    default: {
        m__raw_body = m__io->read_bytes(len()->result());
        break;
    }
    }
}

asn1_der_t::~asn1_der_t() {
    delete m_len;
    if (!n_body) {
        delete m__io__raw_body;
        delete m_body;
    }
}

asn1_der_t::body_sequence_t::body_sequence_t(kaitai::kstream* p__io, asn1_der_t* p__parent, asn1_der_t* p__root) : kaitai::kstruct(p__io) {
    m__parent = p__parent;
    m__root = p__root;
    _read();
}

void asn1_der_t::body_sequence_t::_read() {
    m_entries = new std::vector<asn1_der_t*>();
    {
        int i = 0;
        while (!m__io->is_eof()) {
            m_entries->push_back(new asn1_der_t(m__io));
            i++;
        }
    }
}

asn1_der_t::body_sequence_t::~body_sequence_t() {
    for (std::vector<asn1_der_t*>::iterator it = m_entries->begin(); it != m_entries->end(); ++it) {
        delete *it;
    }
    delete m_entries;
}

asn1_der_t::body_utf8string_t::body_utf8string_t(kaitai::kstream* p__io, asn1_der_t* p__parent, asn1_der_t* p__root) : kaitai::kstruct(p__io) {
    m__parent = p__parent;
    m__root = p__root;
    _read();
}

void asn1_der_t::body_utf8string_t::_read() {
    m_str = kaitai::kstream::bytes_to_str(m__io->read_bytes_full(), std::string("UTF-8"));
}

asn1_der_t::body_utf8string_t::~body_utf8string_t() {
}

asn1_der_t::body_object_id_t::body_object_id_t(kaitai::kstream* p__io, asn1_der_t* p__parent, asn1_der_t* p__root) : kaitai::kstruct(p__io) {
    m__parent = p__parent;
    m__root = p__root;
    f_first = false;
    f_second = false;
    _read();
}

void asn1_der_t::body_object_id_t::_read() {
    m_first_and_second = m__io->read_u1();
    m_rest = m__io->read_bytes_full();
}

asn1_der_t::body_object_id_t::~body_object_id_t() {
}

int32_t asn1_der_t::body_object_id_t::first() {
    if (f_first)
        return m_first;
    m_first = (first_and_second() / 40);
    f_first = true;
    return m_first;
}

int32_t asn1_der_t::body_object_id_t::second() {
    if (f_second)
        return m_second;
    m_second = kaitai::kstream::mod(first_and_second(), 40);
    f_second = true;
    return m_second;
}

asn1_der_t::len_encoded_t::len_encoded_t(kaitai::kstream* p__io, asn1_der_t* p__parent, asn1_der_t* p__root) : kaitai::kstruct(p__io) {
    m__parent = p__parent;
    m__root = p__root;
    f_result = false;
    _read();
}

void asn1_der_t::len_encoded_t::_read() {
    m_b1 = m__io->read_u1();
    n_int2 = true;
    if (b1() == 130) {
        n_int2 = false;
        m_int2 = m__io->read_u2be();
    }
}

asn1_der_t::len_encoded_t::~len_encoded_t() {
    if (!n_int2) {
    }
}

uint16_t asn1_der_t::len_encoded_t::result() {
    if (f_result)
        return m_result;
    m_result = (((b1() & 128) == 0) ? (b1()) : (int2()));
    f_result = true;
    return m_result;
}

asn1_der_t::body_printable_string_t::body_printable_string_t(kaitai::kstream* p__io, asn1_der_t* p__parent, asn1_der_t* p__root) : kaitai::kstruct(p__io) {
    m__parent = p__parent;
    m__root = p__root;
    _read();
}

void asn1_der_t::body_printable_string_t::_read() {
    m_str = kaitai::kstream::bytes_to_str(m__io->read_bytes_full(), std::string("ASCII"));
}

asn1_der_t::body_printable_string_t::~body_printable_string_t() {
}