ASN.1 Datatypes

Java annotations to augment Java classes with information from ASN.1 specifications. These annotations can later be used by encoders like asn1-uper.

Table of Contents:

• Status
• Supported ASN.1 Features
• Design choices
• Examples
  • Example 1: Without restrictions or extension markers
  • Example 2: With Restrictions, no extension markers
  • Example 3: With restrictions and extension markers
• Other ASN.1 tools
• Acknowledgments
• License

Status

Datatypes are enough to handle camdenm. There is no compiler yet, so Java classes and annotations have to be created and added manually.

Supported ASN.1 Features

The following ASN.1 features are implemented:

ASN.1	Java
INTEGER (unconstrained)	BigInteger
INTEGER (constrained)	short, int, long, BigInteger (depending on constraint)
BOOLEAN	boolean
ENUMERATED	enum
SEQUENCE	class
CHOICE	class
BIT STRING (constrained to fixed length)	class
BIT STRING (non-fixed length)	List<Boolean>
OCTET STRING	List<Byte>
IA5String, UTF8String, VisibleString	String
SEQUENCE OF T	List<T> (or SequenceOfT extends Asn1SequenceOf<T>)
SET OF T	also List<T>

Design choices

Design goal was to make the library as clean and simple as possible for the end user, even if it will not be very performant. Inspiration was taken from GSON, where they use reflection to extract fields from classes.

ASN.1 has three major ways to construct complex datatypes: SEQUENCE, CHOICE and SEQUENCE OF. They correspond to struct , union and arrays of C language. (ASN.1 SET and SET OF are pretty much identical to SEQUENCE and SEQUENCE OF, at least for PER, so they are not considered separately).

A SEQUENCE is encoded as an ordinary Java class. Java Reflection API Class.getFields() can return all fields of a class. The documentation says that there is no guarantee on the order in which the fields are returned, however, since Java version 1.6 the fields are returned in the declaration order.

A CHOICE is encoded as an ordinary Java class as well, with exactly one field in the class being non-null, corresponding to the element present.

A SEQUENCE OF is encoded as List<T>. Java type erasure in generics results in the type being lost at run-time if there is no object, so decoding will not work for generics (encoding is fine). So the class have to be non-generic and extend List<T>. GSON allows generic classes by using extra parameters. Scala also solved this issue, using Manifests and implicit parameters. For this library, just making a non-generic wrapper class with a concrete type for List is good enough. To make instantiation of abstract List<T> easier, there is Asn1SequenceOF<T> (it was not possible to extend, for example, ArrayList<T> directly).

OCTET STRING is just a SEQUENCE OF byte. BIT STRING is a SEQUENCE OF boolean. ENUMERATED is an enum.

Integers in ASN.1 are unbounded by default, so BigInteger is used to represent them. If an integer is constrained, then long, int or short will be enough to represent it.

All strings, including IA5String, UTF8String and VisibleString are represented by Java String, the difference is only in annotations.

OPTIONAL is implemented as a nullable field with an annotation. Using built-in Java 8 Optional<T> was not possible due to type erasure, and creating non-generic wrapper classes every time OPTIONAL is used is too much of a burden, so a simple nullable field is used. The name for annotation is @Asn1Optional, to not clash with built-in Optional.

DEFAULT is treated in ASN.1 almost exactly as OPTIONAL, so the annotation from OPTIONAL is used for DEFAULT as well. The only difference is that DEFAULT have a static initializer in the Java class.

ASN.1 restrictions are implemented as Java Annotations. Integers have @IntRange, sequences have @SizeRange and @FixedSize, strings have alphabets etc.

ASN.1 Extensions are marked by annotations too. A sequence that has an extension marker have annotation @HasExtensionMarker, and all elements that come after that marker in ASN.1 are marked with @IsExtension in the Java class. @IntRange() and @SizeRange() also support an optional argument hasExtension=true, which is set to false by default.

Examples

Here's how three examples from the Annex A of the UPER standard (ITU X.691) would be encoded in Java.

Example 1: Without restrictions or extension markers

See this code in action as a part of asn1-uper test suite in UperEncoderExample1BasicTest.java.

ASN.1:

PersonnelRecord ::= [APPLICATION 0] IMPLICIT SET { 
  name Name,
  title [0] VisibleString, 
  number EmployeeNumber, 
  dateOfHire [1] Date, 
  nameOfSpouse [2] Name,
  children [3] IMPLICIT
  SEQUENCE OF ChildInformation DEFAULT {} }

ChildInformation ::= SET { 
  name Name,
  dateOfBirth [0] Date} 

Name ::= [APPLICATION 1] IMPLICIT SEQUENCE { 
  givenName VisibleString,
  initial VisibleString,
  familyName VisibleString }

EmployeeNumber ::= [APPLICATION 2] IMPLICIT INTEGER

Date ::= [APPLICATION 3] IMPLICIT VisibleString -- YYYYMMDD

Corresponding Java code:

@Sequence
public static class PersonenelRecord {
  Name name;
  EmployeeNumber number;
  @RestrictedString(CharacterRestriction.VisibleString)
  String title;
  Date dateOfHire;
  Name nameOfSpouse;
  @Asn1Optional SequenceOfChildInformation sequenceOfChildInformation = new SequenceOfChildInformation();

  public PersonenelRecord() {
  this(new Name(), new EmployeeNumber(), "", new Date(), new Name(), new SequenceOfChildInformation());
  }

  public PersonenelRecord(
    Name name,
    EmployeeNumber number,
    String title,
    Date dateOfHire,
    Name nameOfSpouse,
    SequenceOfChildInformation sequenceOfChildInformation
    ) {
  this.name = name;
  this.number = number;
  this.title = title;
  this.dateOfHire = dateOfHire;
  this.nameOfSpouse = nameOfSpouse;
  this.sequenceOfChildInformation = sequenceOfChildInformation;
  }
}

@Sequence
public static class Name {
  @RestrictedString(CharacterRestriction.VisibleString)
  String givenName;
  @RestrictedString(CharacterRestriction.VisibleString)
  String initial;
  @RestrictedString(CharacterRestriction.VisibleString)
  String familyName;

  public Name() { this("", "", ""); }
  public Name(String givenName, String initial, String familyName) {
  this.givenName = givenName;
  this.initial = initial;
  this.familyName = familyName;
  }
}

public static class EmployeeNumber extends Asn1BigInteger {
  public EmployeeNumber() { this(0); }
  public EmployeeNumber(long value) { this(BigInteger.valueOf(value)); }
  public EmployeeNumber(BigInteger value) { super(value); }
}

@RestrictedString(CharacterRestriction.VisibleString)
public static class Date extends Asn1String {
  public Date() { this(""); }
  public Date(String value) { super(value); }
}

@Sequence
public static class ChildInformation {
  Name name;
  Date dateOfBirth;

  public ChildInformation() { this(new Name(), new Date()); }
  public ChildInformation(Name name, Date dateOfBirth) {
  this.name = name;
  this.dateOfBirth = dateOfBirth;
  }
}

public static class SequenceOfChildInformation extends Asn1SequenceOf<ChildInformation> {
  public SequenceOfChildInformation() { super(); }
  public SequenceOfChildInformation(Collection<ChildInformation> coll) { super(coll); }
}

And the use of those classes:

PersonenelRecord record = new PersonenelRecord(
  new Name(
  "John",
  "P",
  "Smith"
  ),
  new EmployeeNumber(51),
  "Director",
  new Date("19710917"),
  new Name(
  "Mary",
  "T",
  "Smith"),
  new SequenceOfChildInformation(Arrays.asList(
  new ChildInformation(
    new Name(
    "Ralph",
    "T",
    "Smith"
    ),
    new Date("19571111")
  ),
  new ChildInformation(
    new Name(
    "Susan",
    "B",
    "Jones"
    ),
    new Date("19590717")
  )
  ))
);

Example 2: With Restrictions, no extension markers

See code in UperEncoderExample2RestrictionTest.java

ASN.1:

PersonnelRecord ::= [APPLICATION 0] IMPLICIT SET {
  name Name,
  title [0] VisibleString,
  number EmployeeNumber,
  dateOfHire [1] Date,
  nameOfSpouse [2] Name,
  children [3] IMPLICIT
  SEQUENCE OF ChildInformation DEFAULT {} }

ChildInformation ::= SET {
  name Name,
  dateOfBirth [0] Date}

Name ::= [APPLICATION 1] IMPLICIT SEQUENCE {
  givenName NameString,
  initial NameString (SIZE(1)),
  familyName NameString }

EmployeeNumber ::= [APPLICATION 2] IMPLICIT INTEGER

Date ::= [APPLICATION 3] IMPLICIT VisibleString (FROM("0".."9") ^ SIZE(8)) -- YYYYMMDD

NameString ::= VisibleString (FROM("a".."z" | "A".."Z" | "-.") ^ SIZE(1..64))

Java classes:

@Sequence
public static class PersonenelRecord {
  Name name;
  EmployeeNumber number;
  @RestrictedString(CharacterRestriction.VisibleString)
  String title;
  Date dateOfHire;
  Name nameOfSpouse;
  @Asn1Optional SequenceOfChildInformation sequenceOfChildInformation = new SequenceOfChildInformation();

  public PersonenelRecord() {
    this(new Name(), new EmployeeNumber(), "", new Date(), new Name(), new SequenceOfChildInformation());
  }

  public PersonenelRecord(
      Name name,
      EmployeeNumber number,
      String title,
      Date dateOfHire,
      Name nameOfSpouse,
      SequenceOfChildInformation sequenceOfChildInformation
      ) {
    this.name = name;
    this.number = number;
    this.title = title;
    this.dateOfHire = dateOfHire;
    this.nameOfSpouse = nameOfSpouse;
    this.sequenceOfChildInformation = sequenceOfChildInformation;
  }
}

@Sequence
public static class Name {
  NameString givenName;
  @FixedSize(1)
  NameString initial;
  NameString familyName;

  public Name() { this(new NameString(), new NameString(), new NameString()); }
  public Name(NameString givenName, NameString initial, NameString familyName) {
    this.givenName = givenName;
    this.initial = initial;
    this.familyName = familyName;
  }
}

//"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-."
@RestrictedString(value = CharacterRestriction.VisibleString, alphabet = NameString.NameStringAlphabet.class)
@SizeRange(minValue = 1, maxValue = 64)
public static class NameString extends Asn1String {
  public NameString() { this(""); }
  public NameString(String value) { super(value); }

  public static class NameStringAlphabet extends Alphabet {
    private final static String chars =
        new AlphabetBuilder().withRange('a', 'z').withRange('A','Z').withChars("-.").chars();
    public NameStringAlphabet() {
      super(chars);
    }
  }
}

public static class EmployeeNumber extends Asn1BigInteger {
  public EmployeeNumber() { this(0); }
  public EmployeeNumber(long value) { this(BigInteger.valueOf(value)); }
  public EmployeeNumber(BigInteger value) { super(value); }
}

@RestrictedString(value = CharacterRestriction.VisibleString, alphabet = Date.DateAlphabet.class)
@FixedSize(8)
public static class Date extends Asn1String {
  public Date() { this(""); }
  public Date(String value) { super(value); }
  public static class DateAlphabet extends Alphabet {
    private final static String chars = new AlphabetBuilder().withRange('0', '9').chars();
    public DateAlphabet() {
      super(chars);
    }
  }
}

@Sequence
public static class ChildInformation {
  Name name;
  Date dateOfBirth;

  public ChildInformation() { this(new Name(), new Date()); }
  public ChildInformation(Name name, Date dateOfBirth) {
    this.name = name;
    this.dateOfBirth = dateOfBirth;
  }
}

public static class SequenceOfChildInformation extends Asn1SequenceOf<ChildInformation> {
  public SequenceOfChildInformation() { super(); }
  public SequenceOfChildInformation(Collection<ChildInformation> coll) { super(coll); }
}

And example object instantiation:

PersonenelRecord record = new PersonenelRecord(
  new Name(
    new NameString("John"),
    new NameString("P"),
    new NameString("Smith")
  ),
  new EmployeeNumber(51),
  "Director",
  new Date("19710917"),
  new Name(
    new NameString("Mary"),
    new NameString("T"),
    new NameString("Smith")
  ),
  new SequenceOfChildInformation(Arrays.asList(
    new ChildInformation(
      new Name(
        new NameString("Ralph"),
        new NameString("T"),
        new NameString("Smith")
      ),
      new Date("19571111")
    ),
    new ChildInformation(
      new Name(
        new NameString("Susan"),
        new NameString("B"),
        new NameString("Jones")
      ),
      new Date("19590717")
    )
  ))
);

Example 3: With restrictions and extension markers

See code in UperEncoderExample3ExtensionTest.java.

ASN.1 schema:

PersonnelRecord ::= [APPLICATION 0] IMPLICIT SET {
name Name,
title [0] VisibleString, 
number EmployeeNumber, 
dateOfHire [1] Date, 
nameOfSpouse [2] Name,
children [3] IMPLICIT
SEQUENCE (SIZE(2, ...)) OF ChildInformation OPTIONAL,
... }

ChildInformation ::= SET { 
name Name, 
dateOfBirth [0] Date,
...,
sex [1] IMPLICIT ENUMERATED {male(1), female(2),
unknown(3)} OPTIONAL 
}

Name ::= [APPLICATION 1] IMPLICIT SEQUENCE { 
  givenName NameString,
  initial NameString (SIZE(1)),
  familyName NameString,
  ... 
}

EmployeeNumber ::= [APPLICATION 2] IMPLICIT INTEGER (0..9999, ...)

Date ::= [APPLICATION 3] IMPLICIT VisibleString
(FROM("0".."9") ^ SIZE(8, ..., 9..20)) -- YYYYMMDD 

NameString ::= VisibleString
(FROM("a".."z" | "A".."Z" | "-.") ^ SIZE(1..64, ...))

Corresponding Java code:

@Sequence
@HasExtensionMarker
public static class PersonenelRecord {
  Name name;
  EmployeeNumber number;
  @RestrictedString(CharacterRestriction.VisibleString)
  String title;
  Date dateOfHire;
  Name nameOfSpouse;
  @Asn1Optional SequenceOfChildInformation sequenceOfChildInformation;

  public PersonenelRecord() {
    this(new Name(), new EmployeeNumber(), "", new Date(), new Name(), new SequenceOfChildInformation());
  }

  public PersonenelRecord(
      Name name,
      EmployeeNumber number,
      String title,
      Date dateOfHire,
      Name nameOfSpouse,
      SequenceOfChildInformation sequenceOfChildInformation
      ) {
    this.name = name;
    this.number = number;
    this.title = title;
    this.dateOfHire = dateOfHire;
    this.nameOfSpouse = nameOfSpouse;
    this.sequenceOfChildInformation = sequenceOfChildInformation;
  }
}

@Sequence
@HasExtensionMarker
public static class Name {
  NameString givenName;
  @FixedSize(1)
  NameString initial;
  NameString familyName;

  public Name() { this(new NameString(), new NameString(), new NameString()); }
  public Name(NameString givenName, NameString initial, NameString familyName) {
    this.givenName = givenName;
    this.initial = initial;
    this.familyName = familyName;
  }
}

//"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-."
@RestrictedString(value = CharacterRestriction.VisibleString, alphabet = NameString.NameStringAlphabet.class)
@SizeRange(minValue = 1, maxValue = 64, hasExtensionMarker = true)
public static class NameString extends Asn1String {
  public NameString() { this(""); }
  public NameString(String value) { super(value); }

  public static class NameStringAlphabet extends Alphabet {
    private final static String chars =
        new AlphabetBuilder().withRange('a', 'z').withRange('A','Z').withChars("-.").chars();
    public NameStringAlphabet() {
      super(chars);
    }
  }
}

@IntRange(minValue = 0, maxValue = 9999, hasExtensionMarker = true)
public static class EmployeeNumber extends Asn1Integer {
  public EmployeeNumber() { this(0); }
  public EmployeeNumber(long value) { super(value); }
}

@RestrictedString(value = CharacterRestriction.VisibleString, alphabet = Date.DateAlphabet.class)
@SizeRange(minValue = 8, maxValue = 8, hasExtensionMarker = true)
public static class Date extends Asn1String {
  public Date() { this(""); }
  public Date(String value) { super(value); }
  public static class DateAlphabet extends Alphabet {
    private final static String chars = new AlphabetBuilder().withRange('0', '9').chars();
    public DateAlphabet() {
      super(chars);
    }
  }
}

@Sequence
@HasExtensionMarker
public static class ChildInformation {
  Name name;
  Date dateOfBirth;

  @IsExtension
  @Asn1Optional
  Sex sex;

  public ChildInformation() { this(new Name(), new Date()); }
  public ChildInformation(Name name, Date dateOfBirth) {
    this(name, dateOfBirth, null);
  }
  public ChildInformation(Name name, Date dateOfBirth, Sex sex) {
    this.name = name;
    this.dateOfBirth = dateOfBirth;
    this.sex = sex;
  }
}

public static enum Sex {
  male(1),
  female(2),
  unknown(3);

  private final int value;
  public int value() { return value; }
  private Sex(int value) { this.value = value; }
}

@SizeRange(minValue=2, maxValue=2, hasExtensionMarker=true)
public static class SequenceOfChildInformation extends Asn1SequenceOf<ChildInformation> {
  public SequenceOfChildInformation() { super(); }
  public SequenceOfChildInformation(Collection<ChildInformation> coll) { super(coll); }
}

And example instantiation code:

PersonenelRecord record = new PersonenelRecord(
  new Name(
    new NameString("John"),
    new NameString("P"),
    new NameString("Smith")
  ),
  new EmployeeNumber(51),
  "Director",
  new Date("19710917"),
  new Name(
    new NameString("Mary"),
    new NameString("T"),
    new NameString("Smith")
  ),
  new SequenceOfChildInformation(Arrays.asList(
    new ChildInformation(
      new Name(
        new NameString("Ralph"),
        new NameString("T"),
        new NameString("Smith")
      ),
      new Date("19571111")
    ),
    new ChildInformation(
      new Name(
        new NameString("Susan"),
        new NameString("B"),
        new NameString("Jones")
      ),
      new Date("19590717"),
      Sex.female
    )
  ))
);

Other ASN.1 tools

ITU-T have a list of ASN.1 tools. IvmaiAsn project also have its own list.

Here is my (incomplete) list of the open-source tools:

Name	License	Runtime	Compiler	BER, DER?	UPER?
asn1c	BSD 2-clause	C	C	✓	✓
asn1scc	Dual: LGPL, commercial	C, Ada	F#, Antlr/Java	✓	✓
snacc	GPL	C	C, C++	✓
III ASN.1	Mozilla	C++	C++	✓	✓
libtasn1	LGPL	ANSI C99	C	✓ (DER)
pyasn1	BSD 2-clause	Python	asn1ate (Python)	✓
dpkt	BSD 3-Clause	Python	.	✓
libmich	GPLv2	Python	Python	✓	✓
ans1tools	MIT	Python	Python	✓	✓
ASN1js	BSD 3-clause	JavaScript	.	✓
asn1js	MIT	JavaScript	.	✓
node-asn1	MIT	JavaScript	.	✓ (BER)
ASN1.js	MIT	JavaScript	.	✓ (DER)
ASN1s	GPL	Java	Java/Antlr	✓ (BER)
jASN1	LGPL	Java	Java	✓ (BER)
openASN.1	LGPL	Java	Java	✓	✓
asn1forj	GPL	Java	?	✓
JAC	GPL	Java	?	✓ (BER, CER, DER)
JASN	GPL	Java	?	✓ (BER, DER)
Binary Notes	Apache	Java, .NET	XSLT	✓	✓
arc	BSD 4-clause	Java	javacc/Java
Cryptix	BSD 2-clause	Java	SableCC
Legion of The Bouncy Castle	MIT, MIT X11	Java, C#	.	✓ (DER, BER)
Apache Harmony	Apache	Java	.

Acknowledgments

This implementation was partly developed within i-GAME project that has received funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement no 612035.

Use of annotations and reflection was inspired by Gson.

License

This code is released under Apache 2.0 license.