org.apache.xml.security.utils

Class DERDecoderUtils

java.lang.Object

org.apache.xml.security.utils.DERDecoderUtils

public class DERDecoderUtils
extends Object

Provides the means to navigate through a DER-encoded byte array, to help in decoding the contents.

It maintains a "current position" in the array that advances with each operation, providing a simple means to handle the type-length-value encoding of DER. For example

   decoder.expect(TYPE);
   int length = decoder.getLength();
   byte[] value = decoder.getBytes(len);
 

Field Summary

Fields

Modifier and Type	Field and Description
static byte	TYPE_BIT_STRING DER type identifier for a bit string value
static byte	TYPE_OBJECT_IDENTIFIER DER type identifier for ASN.1 "OBJECT IDENTIFIER" value.
static byte	TYPE_OCTET_STRING DER type identifier for a octet string value
static byte	TYPE_SEQUENCE DER type identifier for a sequence value

Constructor Summary

Constructors

Constructor and Description
DERDecoderUtils()

Method Summary

Modifier and Type	Method and Description
static String	decodeOID(byte[] oidBytes) The first two nodes of the OID are encoded onto a single byte.
static byte[]	getAlgorithmIdBytes(InputStream derEncodedIS) Simple method parses an ASN.1 encoded byte array.
static String	getAlgorithmIdFromPublicKey(PublicKey publicKey) The method extracts the algorithm OID from the public key and returns it as "dot encoded" OID string.
static int	readLength(InputStream derEncodedIs) Get the DER length at the current position.
static byte[]	readObjectIdentifier(InputStream derEncodedIS) Read the next object identifier from the given DER-encoded input stream.

Methods inherited from class java.lang.Object

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

Field Detail

TYPE_BIT_STRING

public static final byte TYPE_BIT_STRING

DER type identifier for a bit string value

See Also:

Constant Field Values

TYPE_OCTET_STRING

public static final byte TYPE_OCTET_STRING

DER type identifier for a octet string value

See Also:

Constant Field Values

TYPE_SEQUENCE

public static final byte TYPE_SEQUENCE

DER type identifier for a sequence value

See Also:

Constant Field Values

TYPE_OBJECT_IDENTIFIER

public static final byte TYPE_OBJECT_IDENTIFIER

DER type identifier for ASN.1 "OBJECT IDENTIFIER" value.

See Also:

Constant Field Values

Constructor Detail

DERDecoderUtils

public DERDecoderUtils()

Method Detail

getAlgorithmIdBytes

public static byte[] getAlgorithmIdBytes(InputStream derEncodedIS)
                                  throws DERDecodingException,
                                         IOException

Simple method parses an ASN.1 encoded byte array. The encoding uses "DER", a BER/1 subset, that means a triple { typeId, length, data }. with the following structure:

  PublicKeyInfo ::= SEQUENCE {
      algorithm   AlgorithmIdentifier,
      PublicKey   BIT STRING
  }
 

Where AlgorithmIdentifier is formatted as:

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

Parameters:

derEncodedIS - the DER-encoded input stream to decode.

Throws:

DERDecodingException - in case of decoding error or if given InputStream is null or empty.

IOException - if an I/O error occurs.

readObjectIdentifier

public static byte[] readObjectIdentifier(InputStream derEncodedIS)
                                   throws DERDecodingException

Read the next object identifier from the given DER-encoded input stream.

Parameters:

derEncodedIS - the DER-encoded input stream to decode.

Returns:

the object identifier as a byte array.

Throws:

DERDecodingException - if parse error occurs.

getAlgorithmIdFromPublicKey

public static String getAlgorithmIdFromPublicKey(PublicKey publicKey)
                                          throws DERDecodingException

The method extracts the algorithm OID from the public key and returns it as "dot encoded" OID string.

Parameters:

publicKey - the public key for which method returns algorithm ID.

Returns:

String representing the algorithm ID.

Throws:

DERDecodingException - if the algorithm ID cannot be determined.

readLength

public static int readLength(InputStream derEncodedIs)
                      throws DERDecodingException,
                             IOException

Get the DER length at the current position.

DER length is encoded as

• If the first byte is 0x00 to 0x7F, it describes the actual length.
• If the first byte is 0x80 + n with 0The length value 0x80, used only in constructed types, is defined as "indefinite length".

Returns:

the length, -1 for indefinite length.

Throws:

DERDecodingException - if the current position is at the end of the array or there is an incomplete length specification.

IOException - if an I/O error occurs.

decodeOID

public static String decodeOID(byte[] oidBytes)

The first two nodes of the OID are encoded onto a single byte. The first node is multiplied by the decimal 40 and the result is added to the value of the second node. Node values less than or equal to 127 are encoded in one byte. Node values greater than or equal to 128 are encoded on multiple bytes. Bit 7 of the leftmost byte is set to one. Bits 0 through 6 of each byte contains the encoded value.

Parameters:

oidBytes - the byte array containing the OID

Returns:

the decoded OID as a string