schemajic.encoder
Class ASN1Helper

java.lang.Object
  schemajic.encoder.ASN1Helper

public class ASN1Helper
extends java.lang.Object

Useful tools that help DER encoding values of ASN.1 types.

Version:

1.00 - 2006/02/10

Author:

support@phillipgriffin.com

Field Summary

static byte	HIGH_BIT Defines the "high bit" that is the sign extension bit for a 8-bit signed value.
static byte	TAG_CLASS
static byte	TAG_PC

Method Summary

int	buildHeader(byte[] buf, int startOffset, int asnLength) Encodes an ASN.1 header into the given byte buffer in support of the AsnEncoder interface.
int	buildLength(byte[] buf, int startOffset, int asnLength) The buildLength() method is used to encode an ASN.1 vlaue length into the specified byte buffer.
int	buildObjectId(byte[] buffer, int startOffset, int[] arcs) The buildObjectId() method is used to encode an ASN.1 object id value into the specified byte buffer.
int	buildRelativeObjectId(byte[] buffer, int startOffset, int[] arcs) The buildObjectId() method is used to encode an ASN.1 object id value into the specified byte buffer.
int	calcOidLengthInBytes(int[] arcs) Calculates the length of a value of ASN.1 type OBJECT IDENTIFIER in octets.
int	calcRidLengthInBytes(int[] arcs) Calculates the length of a value of ASN.1 type RELATIVE-OID in octets.
int	decode7BitEncodedInteger(java.io.InputStream buffer) Given a tag class, pc and tag value, create an instance of the appropriate Tag subclass.
protected void	encodeLongTag(int tag, java.io.OutputStream out) A 'tag number' was > 30, and therefore must be encoded in multiple octets, each with 7 significant bits.
protected void	encodeShortTag(int tag, java.io.OutputStream out) A 'tag number' is < 31, and therefore it may be encoded in a single octet.
static ASN1Helper	getInstance() Returns the current instance or a new instance of ASN1Helper
int	getIntegerLengthInBits(int i) Returns the minimum number of octets required to hold the value of the specified integer.
int	getIntegerLengthInBytes(int i) Returns the minimum number of octets required to hold the value of the specified integer.
protected static void	rotate(byte[] buf, int begin, int pivot, int end) Rotates a give buffer area marked by begin, pivot, and end.

Methods inherited from class java.lang.Object

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

Field Detail

HIGH_BIT

public static final byte HIGH_BIT

Defines the "high bit" that is the sign extension bit for a 8-bit signed value.

See Also:

Constant Field Values

TAG_CLASS

public static final byte TAG_CLASS

See Also:

Constant Field Values

TAG_PC

public static final byte TAG_PC

See Also:

Constant Field Values

Method Detail

getInstance

public static ASN1Helper getInstance()

Returns the current instance or a new instance of ASN1Helper

getIntegerLengthInBytes

public int getIntegerLengthInBytes(int i)

Returns the minimum number of octets required to hold the value of the specified integer.

getIntegerLengthInBits

public int getIntegerLengthInBits(int i)

Returns the minimum number of octets required to hold the value of the specified integer.

Only suuports integers of 31 bits or less, as the Java int type is signed.

Parameters:

i - a provided length

Returns:

the length in bits

calcOidLengthInBytes

public int calcOidLengthInBytes(int[] arcs)

Calculates the length of a value of ASN.1 type OBJECT IDENTIFIER in octets.

Parameters:

arcs - a series of OID arcs

Returns:

the length of an ASN.1 information object identifier

calcRidLengthInBytes

public int calcRidLengthInBytes(int[] arcs)

Calculates the length of a value of ASN.1 type RELATIVE-OID in octets.

Parameters:

arcs - a series of relative OID arcs

Returns:

the length of an ASN.1 relative information object identifier

buildHeader

public int buildHeader(byte[] buf,
                       int startOffset,
                       int asnLength)
                throws java.io.IOException

Encodes an ASN.1 header into the given byte buffer in support of the AsnEncoder interface. This method is dependant on the buildLength() method.

Parameters:

buf - an output buffer of encoded octets (bytes)

startOffset - offset from the start of the buffer where the method should start writing the encoded data

asnLength - length to be encoded

Returns:

the new offset for the next encoding routine. If startOffset is subtracted from the return value then the length of the encoded data can be determined

Throws:

java.io.IOException

buildLength

public int buildLength(byte[] buf,
                       int startOffset,
                       int asnLength)
                throws java.io.IOException

The buildLength() method is used to encode an ASN.1 vlaue length into the specified byte buffer. The method is defined in the AsnEncoder interface.

Parameters:

buf - The output buffer of encoded bytes.

startOffset - The offset from the start of the buffer where the method should start writing the encoded data.

asnLength - The length to be encoded.

Returns:

Returns the new offset for the next encoding routine. If the startOffset is subtracted from the return value then the length of the encoded data can be determined.

Throws:

java.io.IOException

buildObjectId

public int buildObjectId(byte[] buffer,
                         int startOffset,
                         int[] arcs)
                  throws java.io.IOException

The buildObjectId() method is used to encode an ASN.1 object id value into the specified byte buffer.

Parameters:

buffer - The output buffer of encoded bytes.

startOffset - The offset from the start of the buffer where the method should start writing the encoded data.

arcs - An array of integers to encode.

Returns:

Returns the new offset for the next encoding routine. If startOffset is subtracted from the return value then the length of the encoded data can be determined.

Throws:

java.io.IOException

buildRelativeObjectId

public int buildRelativeObjectId(byte[] buffer,
                                 int startOffset,
                                 int[] arcs)
                          throws java.io.IOException

The buildObjectId() method is used to encode an ASN.1 object id value into the specified byte buffer.

Parameters:

buffer - The output buffer of encoded bytes.

startOffset - The offset from the start of the buffer where the method should start writing the encoded data.

arcs - An array of integers to encode.

Returns:

Returns the new offset for the next encoding routine. If startOffset is subtracted from the return value then the length of the encoded data can be determined.

Throws:

java.io.IOException - Thrown if an error occurs encoding the datatype.

encodeShortTag

protected void encodeShortTag(int tag,
                              java.io.OutputStream out)
                       throws java.io.IOException

A 'tag number' is < 31, and therefore it may be encoded in a single octet.

Throws:

java.io.IOException

encodeLongTag

protected void encodeLongTag(int tag,
                             java.io.OutputStream out)
                      throws java.io.IOException

A 'tag number' was > 30, and therefore must be encoded in multiple octets, each with 7 significant bits.

Throws:

java.io.IOException

rotate

protected static void rotate(byte[] buf,
                             int begin,
                             int pivot,
                             int end)
                      throws java.lang.ArrayIndexOutOfBoundsException

Rotates a give buffer area marked by begin, pivot, and end. The pivot marks the point where the bytes between [pivot..end) are moved to the position marked by begin. The bytes between [begin..pivot) are shifted such that begin is at [begin+(end-pivot)].

Parameters:

buf - The buffer containing the data to rotate

begin - The start of the rotation

pivot - The pivot point for the rotation

end - The end of the rotational buffer

Throws:

java.lang.ArrayIndexOutOfBoundsException - Thrown if an access exception occurs

decode7BitEncodedInteger

public int decode7BitEncodedInteger(java.io.InputStream buffer)
                             throws DecodingException

Given a tag class, pc and tag value, create an instance of the appropriate Tag subclass. private Tag createTag( int tagClass, int tagPC, int tagValue ) throws DecodingException { int u = Tag.UNIVERSAL; int c = Tag.CONTEXT_SPECIFIC; // Cast tagClass to a byte so sign doesn't interfere with // comparison to Tag class constants. switch ( ( byte ) tagClass ) { case Tag.UNIVERSAL: return new UniversalTag( tagValue, tagPC ); case Tag.CONTEXT_SPECIFIC: return new ContextSpecificTag( tagValue, tagPC ); default: throw new DecodingException( "unknown tag class:" + tagClass ); } }

Throws:

DecodingException