com.entrust.toolkit.asn1

Class Asn1EncodingConverter

java.lang.Object

com.entrust.toolkit.asn1.Asn1EncodingConverter

public class Asn1EncodingConverter
extends java.lang.Object

This class is a utility for converting indefinite length BER encoded ASN1 to definite length BER encoded ASN1.

The conversion is a multi-stage process. First, the BER encoded data is read to obtain the structure. Next, that structure is converted to the equivalent definite length encoding. Finally, the BER encoded data is read again, and written to another stream using the calculated definite length encoding.

To perform the conversion, the entire ASN1 structure must be read in to memory. Memory requirements will vary depending on the complexity of the structure. This class operates well when constructed string types are constructed using runs of the same length, such as those produced by PKCS7EncodeStream when the block size is set. If the ASN1 uses many different tags and length encodings, OutOfMemoryErrors may occur.

There are some important limitations to this class:

• It does not check for valid ASN1 encoding of the input. For example, it does not check that any INTEGER type read in uses primitive encoding. If the input can be parsed as at least looking like, ASN1, the output will be just as valid or invalid as the input.
• It only works if the ASN.1 tag and length values for each data structure are encoding using the minimum number of bytes required. For example, while NULL can be encoded as 0x05 0x00 or 0x05 0x81 0x00, only the former encoding will result in correct output.
• It does not convert BER to DER, only indefinite length to definite length.
• It does not require that the input uses indefinite length encoding, and may convert definite length to definite length.
• While it can convert greater than 2GB of data to definite length encoding, this is generally not a good idea as most ASN1 parsers use a signed 32 bit integer for length values, and more than 2GB will cause arithmetic overflow and unpredictable results.

Since:

7.0

Method Summary

Modifier and Type	Method and Description
static void	convertEncoding(java.io.InputStream is1, java.io.InputStream is2, java.io.OutputStream os) Converts the ASN1 data in a stream to definite length encoding and writes it to another stream.
static void	convertEncoding(java.lang.String inFileName, java.lang.String outFileName) Converts the ASN1 data in a file to definite length encoding and writes it to another file.

Methods inherited from class java.lang.Object

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

Method Detail

convertEncoding

public static void convertEncoding(java.lang.String inFileName,
                                   java.lang.String outFileName)
                            throws CodingException,
                                   java.io.IOException

Converts the ASN1 data in a file to definite length encoding and writes it to another file.

Parameters:

inFileName - the name of the file that contains the indefinite length encoded data.

outFileName - the name of the file to which the definite length encoded data will be written. This must be refer to a different file from inFileName

Throws:

CodingException - if the data in inFileName cannot be parsed as ASN1.

java.io.IOException - if there is any IO problem reading or writing the files.

convertEncoding

public static void convertEncoding(java.io.InputStream is1,
                                   java.io.InputStream is2,
                                   java.io.OutputStream os)
                            throws CodingException,
                                   java.io.IOException

Converts the ASN1 data in a stream to definite length encoding and writes it to another stream. As this is a two-pass operation, two input stream on the same data are required. All of the streams will be closed when this method completes.

Parameters:

is1 - the stream from which the structure of the ASN1 encoded data will be parsed.

is2 - the stream from which the ASN1 encoded data will be read. This stream must contain identical data to is1, but not be the same stream. If the data is not identical, the data written to os will be meaningless.

os - the output stream to write the definite length encoded data to.

Throws:

CodingException - if the data in is1 cannot be parsed as ASN1.

java.io.IOException - if there is any IO problem reading or writing the streams.