codec.asn1
Class ASN1

java.lang.Object
  |
  +--codec.asn1.ASN1

public final class ASN1

extends Object

Defines various constants used with ASN.1 such as the tag and type class identifiers. The classes in this package are modelled along the lines of ITU-T Recommendations X.680, X.681, X.682, X.690, and X.691. From now on we assume the reader is familiar with ASN.1, BER, and DER.

This package defines a number of primitive types as specified by the basic syntax in X.680. Based on these primitive types more complex types can be created. We refer to these types as compound types or structures. Below, we discuss how such types are constructed, encoded and decoded using the classes in this package.

For instance the type PrivateKeyInfo is defined in PKCS#8 as follows using ASN.1:

 PrivateKeyInfo ::= SEQUENCE (
   version Version,
   privateKeyAlgorithm PrivateKeyAlgorithmIdentifier,
   privateKey PrivateKey,
   attributes [0] IMPLICIT Attributes OPTIONAL
 }
 Version ::= INTEGER
 PrivateKeyAlgorithmIdentifier ::= AlgorithmIdentifier
 PrivateKey ::= OCTET STRING
 Attributes ::= SET OF Attribute
 

This type can be created as follows based on the classes in this package:

 public class PrivateKeyInfo extends ASN1Sequence
  {
    public PrivateKeyInfo()
     {
       add(new ASN1Integer());
       add(new AlgorithmIdentifier()); // Detailed below
       add(new ASN1OctetString());
       add(new ASN1TaggedType(
         0, new ASN1SetOf(Attribute.class), false, true);
     }
    ...
  }
 

The tagged type allows to define types of the ASN.1 tag class UNIVERSAL, CONTEXT SPECIFIC, APPLICATION, and PRIVATE. The constructor shown above is a convenience constructor that assumes the class is CONTEXT SPECIFIC. The third parameter specifies that the tagging is not EXPLICIT (hence IMPLICIT as required by the definition above), and the fourth parameter specifies that attributes is OPTIONAL.

The interface ASN1Type specifies a number of methods to declare types as OPTIONAL, IMPLICIT or EXPLICIT. In principle, ASN.1 structures can be modelled almost one to one using the classes in this package.

Individual types also offer setter methods and constructors that allow to preset certain values as the values of the ASN.1 types from native Java types such as String, int, byte[] etc.

Once, a primitive type or a compound type x has been defined and initialized it can be encoded in a number of ways. The first step is to choose an encoder. One example encoder is the DEREncoder. This encoder encodes types according to the Distinguished Encoding Rules, a subset of the Basic Encoding Rules defined in the ITU-T Recommendations. Encoding to a file is simple, the following code snippet shows how to do it:

 DEREncoder enc;
 enc = new DEREncoder(new FileOutputStream("code.der"));
 enc.writeType(x);
 enc.close();
 

There is nothing more to it. However, only types not declared as OPTIONAL are written to the stream. Hence, the type attributes mentioned above is not written.

Why then is it declared as OPTIONAL? Answer, by convention in this package (and by reason) the default constructor is meant to initialize a type for decoding. In a code the attributes type can be encountered. The decoder clears the OPTIONAL flag of types it encounters during decoding so it is clear which types were present and which were not. If a type is only used for encoding and not for decoding then the OPTIONAL types not required can be omitted.

 AlgorithmIdentifier  ::= SEQUENCE{
   algorithm  OBJECT IDENTIFIER,
   parameters ANY DEFINED BY algorithm OPTIONAL
 }
 

Version:

"$Id: ASN1.java,v 1.4 2005/03/22 16:04:37 flautens Exp $"

Author:

Volker Roth

Field Summary

static int	CLASS_APPLICATION DOCUMENT ME!
static int	CLASS_CONTEXT DOCUMENT ME!
static int	CLASS_MASK DOCUMENT ME!
static int	CLASS_PRIVATE DOCUMENT ME!
static int	CLASS_UNIVERSAL DOCUMENT ME!
static int	CONSTRUCTED DOCUMENT ME!
static int	LENGTH_LONGFORM DOCUMENT ME!
static int	LENGTH_MASK DOCUMENT ME!
static int	PRIMITIVE DOCUMENT ME!
static int	TAG_BITSTRING DOCUMENT ME!
static int	TAG_BMPSTRING DOCUMENT ME!
static int	TAG_BOOLEAN DOCUMENT ME!
static int	TAG_ENUMERATED DOCUMENT ME!
static int	TAG_EOC DOCUMENT ME!
static int	TAG_GENERALIZEDTIME DOCUMENT ME!
static int	TAG_GENERALSTRING DOCUMENT ME!
static int	TAG_GRAPHICSTRING DOCUMENT ME!
static int	TAG_IA5STRING DOCUMENT ME!
static int	TAG_INTEGER DOCUMENT ME!
static int	TAG_LONGFORM DOCUMENT ME!
static int	TAG_MASK DOCUMENT ME!
static int	TAG_NULL DOCUMENT ME!
static int	TAG_NUMERICSTRING DOCUMENT ME!
static int	TAG_OCTETSTRING DOCUMENT ME!
static int	TAG_OID DOCUMENT ME!
static int	TAG_PRINTABLESTRING DOCUMENT ME!
static int	TAG_REAL DOCUMENT ME!
static int	TAG_SEQUENCE DOCUMENT ME!
static int	TAG_SET DOCUMENT ME!
static int	TAG_T61STRING DOCUMENT ME!
static int	TAG_UNIVERSALSTRING DOCUMENT ME!
static int	TAG_UTCTIME DOCUMENT ME!
static int	TAG_UTF8STRING DOCUMENT ME!
static int	TAG_VIDEOTEXTSTRING DOCUMENT ME!
static int	TAG_VISIBLESTRING DOCUMENT ME!

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

TAG_EOC

public static final int TAG_EOC

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TAG_BOOLEAN

public static final int TAG_BOOLEAN

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TAG_INTEGER

public static final int TAG_INTEGER

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TAG_BITSTRING

public static final int TAG_BITSTRING

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TAG_OCTETSTRING

public static final int TAG_OCTETSTRING

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TAG_NULL

public static final int TAG_NULL

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TAG_OID

public static final int TAG_OID

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TAG_REAL

public static final int TAG_REAL

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TAG_ENUMERATED

public static final int TAG_ENUMERATED

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TAG_UTF8STRING

public static final int TAG_UTF8STRING

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TAG_SEQUENCE

public static final int TAG_SEQUENCE

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TAG_SET

public static final int TAG_SET

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TAG_NUMERICSTRING

public static final int TAG_NUMERICSTRING

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TAG_PRINTABLESTRING

public static final int TAG_PRINTABLESTRING

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TAG_T61STRING

public static final int TAG_T61STRING

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TAG_VIDEOTEXTSTRING

public static final int TAG_VIDEOTEXTSTRING

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TAG_IA5STRING

public static final int TAG_IA5STRING

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TAG_UTCTIME

public static final int TAG_UTCTIME

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TAG_GENERALIZEDTIME

public static final int TAG_GENERALIZEDTIME

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TAG_GRAPHICSTRING

public static final int TAG_GRAPHICSTRING

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TAG_VISIBLESTRING

public static final int TAG_VISIBLESTRING

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TAG_GENERALSTRING

public static final int TAG_GENERALSTRING

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TAG_UNIVERSALSTRING

public static final int TAG_UNIVERSALSTRING

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TAG_BMPSTRING

public static final int TAG_BMPSTRING

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TAG_MASK

public static final int TAG_MASK

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TAG_LONGFORM

public static final int TAG_LONGFORM

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CLASS_UNIVERSAL

public static final int CLASS_UNIVERSAL

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CLASS_APPLICATION

public static final int CLASS_APPLICATION

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CLASS_CONTEXT

public static final int CLASS_CONTEXT

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CLASS_PRIVATE

public static final int CLASS_PRIVATE

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CLASS_MASK

public static final int CLASS_MASK

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PRIMITIVE

public static final int PRIMITIVE

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CONSTRUCTED

public static final int CONSTRUCTED

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LENGTH_LONGFORM

public static final int LENGTH_LONGFORM

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LENGTH_MASK

public static final int LENGTH_MASK

DOCUMENT ME!