http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.7. 
package org.bouncycastle.asn1.x509;

import java.io.IOException;
import java.util.StringTokenizer;

import org.bouncycastle.asn1.ASN1Choice;
import org.bouncycastle.asn1.ASN1Encodable;
import org.bouncycastle.asn1.ASN1Object;
import org.bouncycastle.asn1.ASN1OctetString;
import org.bouncycastle.asn1.ASN1Sequence;
import org.bouncycastle.asn1.ASN1TaggedObject;
import org.bouncycastle.asn1.DEREncodable;
import org.bouncycastle.asn1.DERIA5String;
import org.bouncycastle.asn1.DERObject;
import org.bouncycastle.asn1.DERObjectIdentifier;
import org.bouncycastle.asn1.DEROctetString;
import org.bouncycastle.asn1.DERTaggedObject;
import org.bouncycastle.asn1.x500.X500Name;
import org.bouncycastle.util.IPAddress;


The GeneralName object.

GeneralName ::= CHOICE {
     otherName                       [0]     OtherName,
     rfc822Name                      [1]     IA5String,
     dNSName                         [2]     IA5String,
     x400Address                     [3]     ORAddress,
     directoryName                   [4]     Name,
     ediPartyName                    [5]     EDIPartyName,
     uniformResourceIdentifier       [6]     IA5String,
     iPAddress                       [7]     OCTET STRING,
     registeredID                    [8]     OBJECT IDENTIFIER}
OtherName ::= SEQUENCE {
     type-id    OBJECT IDENTIFIER,
     value      [0] EXPLICIT ANY DEFINED BY type-id }
EDIPartyName ::= SEQUENCE {
     nameAssigner            [0]     DirectoryString OPTIONAL,
     partyName               [1]     DirectoryString }
Name ::= CHOICE { RDNSequence }



/**
 * The GeneralName object.
 * <pre>
 * GeneralName ::= CHOICE {
 *      otherName                       [0]     OtherName,
 *      rfc822Name                      [1]     IA5String,
 *      dNSName                         [2]     IA5String,
 *      x400Address                     [3]     ORAddress,
 *      directoryName                   [4]     Name,
 *      ediPartyName                    [5]     EDIPartyName,
 *      uniformResourceIdentifier       [6]     IA5String,
 *      iPAddress                       [7]     OCTET STRING,
 *      registeredID                    [8]     OBJECT IDENTIFIER}
 *
 * OtherName ::= SEQUENCE {
 *      type-id    OBJECT IDENTIFIER,
 *      value      [0] EXPLICIT ANY DEFINED BY type-id }
 *
 * EDIPartyName ::= SEQUENCE {
 *      nameAssigner            [0]     DirectoryString OPTIONAL,
 *      partyName               [1]     DirectoryString }
 * 
 * Name ::= CHOICE { RDNSequence }
 * </pre>
 */
public class GeneralName
    extends ASN1Encodable
    implements ASN1Choice
{
    public static final int otherName                     = 0;
    public static final int rfc822Name                    = 1;
    public static final int dNSName                       = 2;
    public static final int x400Address                   = 3;
    public static final int directoryName                 = 4;
    public static final int ediPartyName                  = 5;
    public static final int uniformResourceIdentifier     = 6;
    public static final int iPAddress                     = 7;
    public static final int registeredID                  = 8;

    DEREncodable      obj;
    int               tag;
   
    public GeneralName(
        X509Name  dirName)
    {
        this.obj = dirName;
        this.tag = 4;
    }

    public GeneralName(
        X500Name dirName)
    {
        this.obj = dirName;
        this.tag = 4;
    }

    
Deprecated:this constructor seems the wrong way round! Use GeneralName(tag, name).
/**
     * @deprecated this constructor seems the wrong way round! Use GeneralName(tag, name).
     */
    public GeneralName(
        DERObject name, int tag)
    {
        this.obj = name;
        this.tag = tag;
    }

    
When the subjectAltName extension contains an Internet mail address,
the address MUST be included as an rfc822Name. The format of an
rfc822Name is an "addr-spec" as defined in RFC 822 [RFC 822].
When the subjectAltName extension contains a domain name service
label, the domain name MUST be stored in the dNSName (an IA5String).
The name MUST be in the "preferred name syntax," as specified by RFC
1034 [RFC 1034].
When the subjectAltName extension contains a URI, the name MUST be
stored in the uniformResourceIdentifier (an IA5String). The name MUST
be a non-relative URL, and MUST follow the URL syntax and encoding
rules specified in [RFC 1738].  The name must include both a scheme
(e.g., "http" or "ftp") and a scheme-specific-part.  The scheme-
specific-part must include a fully qualified domain name or IP
address as the host.
When the subjectAltName extension contains a iPAddress, the address
MUST be stored in the octet string in "network byte order," as
specified in RFC 791 [RFC 791]. The least significant bit (LSB) of
each octet is the LSB of the corresponding byte in the network
address. For IP Version 4, as specified in RFC 791, the octet string
MUST contain exactly four octets.  For IP Version 6, as specified in
RFC 1883, the octet string MUST contain exactly sixteen octets [RFC
1883].

/**
     * When the subjectAltName extension contains an Internet mail address,
     * the address MUST be included as an rfc822Name. The format of an
     * rfc822Name is an "addr-spec" as defined in RFC 822 [RFC 822].
     *
     * When the subjectAltName extension contains a domain name service
     * label, the domain name MUST be stored in the dNSName (an IA5String).
     * The name MUST be in the "preferred name syntax," as specified by RFC
     * 1034 [RFC 1034].
     *
     * When the subjectAltName extension contains a URI, the name MUST be
     * stored in the uniformResourceIdentifier (an IA5String). The name MUST
     * be a non-relative URL, and MUST follow the URL syntax and encoding
     * rules specified in [RFC 1738].  The name must include both a scheme
     * (e.g., "http" or "ftp") and a scheme-specific-part.  The scheme-
     * specific-part must include a fully qualified domain name or IP
     * address as the host.
     *
     * When the subjectAltName extension contains a iPAddress, the address
     * MUST be stored in the octet string in "network byte order," as
     * specified in RFC 791 [RFC 791]. The least significant bit (LSB) of
     * each octet is the LSB of the corresponding byte in the network
     * address. For IP Version 4, as specified in RFC 791, the octet string
     * MUST contain exactly four octets.  For IP Version 6, as specified in
     * RFC 1883, the octet string MUST contain exactly sixteen octets [RFC
     * 1883].
     */
    public GeneralName(
        int           tag,
        ASN1Encodable name)
    {
        this.obj = name;
        this.tag = tag;
    }
    
    
Create a GeneralName for the given tag from the passed in String.


This constructor can handle:

    

  • rfc822Name

  • iPAddress

  • directoryName

  • dNSName

  • uniformResourceIdentifier

  • registeredID


For x400Address, otherName and ediPartyName there is no common string
format defined.


Note: A directory name can be encoded in different ways into a byte
representation. Be aware of this if the byte representation is used for
comparing results.

Params:
  • tag – tag number
  • name – string representation of name
Throws:
/**
     * Create a GeneralName for the given tag from the passed in String.
     * <p>
     * This constructor can handle:
     * <ul>
     * <li>rfc822Name
     * <li>iPAddress
     * <li>directoryName
     * <li>dNSName
     * <li>uniformResourceIdentifier
     * <li>registeredID
     * </ul>
     * For x400Address, otherName and ediPartyName there is no common string
     * format defined.
     * <p>
     * Note: A directory name can be encoded in different ways into a byte
     * representation. Be aware of this if the byte representation is used for
     * comparing results.
     *
     * @param tag tag number
     * @param name string representation of name
     * @throws IllegalArgumentException if the string encoding is not correct or     *             not supported.
     */
    public GeneralName(
        int       tag,
        String    name)
    {
        this.tag = tag;

        if (tag == rfc822Name || tag == dNSName || tag == uniformResourceIdentifier)
        {
            this.obj = new DERIA5String(name);
        }
        else if (tag == registeredID)
        {
            this.obj = new DERObjectIdentifier(name);
        }
        else if (tag == directoryName)
        {
            this.obj = new X509Name(name);
        }
        else if (tag == iPAddress)
        {
            byte[] enc = toGeneralNameEncoding(name);
            if (enc != null)
            {
                this.obj = new DEROctetString(enc);
            }
            else
            {
                throw new IllegalArgumentException("IP Address is invalid");
            }
        }
        else
        {
            throw new IllegalArgumentException("can't process String for tag: " + tag);
        }
    }
    
    public static GeneralName getInstance(
        Object obj)
    {
        if (obj == null || obj instanceof GeneralName)
        {
            return (GeneralName)obj;
        }

        if (obj instanceof ASN1TaggedObject)
        {
            ASN1TaggedObject    tagObj = (ASN1TaggedObject)obj;
            int                 tag = tagObj.getTagNo();

            switch (tag)
            {
            case otherName:
                return new GeneralName(tag, ASN1Sequence.getInstance(tagObj, false));
            case rfc822Name:
                return new GeneralName(tag, DERIA5String.getInstance(tagObj, false));
            case dNSName:
                return new GeneralName(tag, DERIA5String.getInstance(tagObj, false));
            case x400Address:
                throw new IllegalArgumentException("unknown tag: " + tag);
            case directoryName:
                return new GeneralName(tag, X509Name.getInstance(tagObj, true));
            case ediPartyName:
                return new GeneralName(tag, ASN1Sequence.getInstance(tagObj, false));
            case uniformResourceIdentifier:
                return new GeneralName(tag, DERIA5String.getInstance(tagObj, false));
            case iPAddress:
                return new GeneralName(tag, ASN1OctetString.getInstance(tagObj, false));
            case registeredID:
                return new GeneralName(tag, DERObjectIdentifier.getInstance(tagObj, false));
            }
        }

        if (obj instanceof byte[])
        {
            try
            {
                return getInstance(ASN1Object.fromByteArray((byte[])obj));
            }
            catch (IOException e)
            {
                throw new IllegalArgumentException("unable to parse encoded general name");
            }
        }

        throw new IllegalArgumentException("unknown object in getInstance: " + obj.getClass().getName());
    }

    public static GeneralName getInstance(
        ASN1TaggedObject tagObj,
        boolean          explicit)
    {
        return GeneralName.getInstance(ASN1TaggedObject.getInstance(tagObj, true));
    }

    public int getTagNo()
    {
        return tag;
    }

    public DEREncodable getName()
    {
        return obj;
    }

    public String toString()
    {
        StringBuffer buf = new StringBuffer();

        buf.append(tag);
        buf.append(": ");
        switch (tag)
        {
        case rfc822Name:
        case dNSName:
        case uniformResourceIdentifier:
            buf.append(DERIA5String.getInstance(obj).getString());
            break;
        case directoryName:
            buf.append(X509Name.getInstance(obj).toString());
            break;
        default:
            buf.append(obj.toString());
        }
        return buf.toString();
    }

    private byte[] toGeneralNameEncoding(String ip)
    {
        if (IPAddress.isValidIPv6WithNetmask(ip) || IPAddress.isValidIPv6(ip))
        {
            int    slashIndex = ip.indexOf('/');

            if (slashIndex < 0)
            {
                byte[] addr = new byte[16];
                int[]  parsedIp = parseIPv6(ip);
                copyInts(parsedIp, addr, 0);

                return addr;
            }
            else
            {
                byte[] addr = new byte[32];
                int[]  parsedIp = parseIPv6(ip.substring(0, slashIndex));
                copyInts(parsedIp, addr, 0);
                String mask = ip.substring(slashIndex + 1);
                if (mask.indexOf(':') > 0)
                {
                    parsedIp = parseIPv6(mask);
                }
                else
                {
                    parsedIp = parseMask(mask);
                }
                copyInts(parsedIp, addr, 16);

                return addr;
            }
        }
        else if (IPAddress.isValidIPv4WithNetmask(ip) || IPAddress.isValidIPv4(ip))
        {
            int    slashIndex = ip.indexOf('/');

            if (slashIndex < 0)
            {
                byte[] addr = new byte[4];

                parseIPv4(ip, addr, 0);

                return addr;
            }
            else
            {
                byte[] addr = new byte[8];

                parseIPv4(ip.substring(0, slashIndex), addr, 0);

                String mask = ip.substring(slashIndex + 1);
                if (mask.indexOf('.') > 0)
                {
                    parseIPv4(mask, addr, 4);
                }
                else
                {
                    parseIPv4Mask(mask, addr, 4);
                }

                return addr;
            }
        }

        return null;
    }

    private void parseIPv4Mask(String mask, byte[] addr, int offset)
    {
        int   maskVal = Integer.parseInt(mask);

        for (int i = 0; i != maskVal; i++)
        {
            addr[(i / 8) + offset] |= 1 << (i % 8);
        }
    }

    private void parseIPv4(String ip, byte[] addr, int offset)
    {
        StringTokenizer sTok = new StringTokenizer(ip, "./");
        int    index = 0;

        while (sTok.hasMoreTokens())
        {
            addr[offset + index++] = (byte)Integer.parseInt(sTok.nextToken());
        }
    }

    private int[] parseMask(String mask)
    {
        int[] res = new int[8];
        int   maskVal = Integer.parseInt(mask);

        for (int i = 0; i != maskVal; i++)
        {
            res[i / 16] |= 1 << (i % 16);
        }
        return res;
    }

    private void copyInts(int[] parsedIp, byte[] addr, int offSet)
    {
        for (int i = 0; i != parsedIp.length; i++)
        {
            addr[(i * 2) + offSet] = (byte)(parsedIp[i] >> 8);
            addr[(i * 2 + 1) + offSet] = (byte)parsedIp[i];
        }
    }

    private int[] parseIPv6(String ip)
    {
        StringTokenizer sTok = new StringTokenizer(ip, ":", true);
        int index = 0;
        int[] val = new int[8];

        if (ip.charAt(0) == ':' && ip.charAt(1) == ':')
        {
           sTok.nextToken(); // skip the first one
        }

        int doubleColon = -1;

        while (sTok.hasMoreTokens())
        {
            String e = sTok.nextToken();

            if (e.equals(":"))
            {
                doubleColon = index;
                val[index++] = 0;
            }
            else
            {
                if (e.indexOf('.') < 0)
                {
                    val[index++] = Integer.parseInt(e, 16);
                    if (sTok.hasMoreTokens())
                    {
                        sTok.nextToken();
                    }
                }
                else
                {
                    StringTokenizer eTok = new StringTokenizer(e, ".");

                    val[index++] = (Integer.parseInt(eTok.nextToken()) << 8) | Integer.parseInt(eTok.nextToken());
                    val[index++] = (Integer.parseInt(eTok.nextToken()) << 8) | Integer.parseInt(eTok.nextToken());
                }
            }
        }

        if (index != val.length)
        {
            System.arraycopy(val, doubleColon, val, val.length - (index - doubleColon), index - doubleColon);
            for (int i = doubleColon; i != val.length - (index - doubleColon); i++)
            {
                val[i] = 0;
            }
        }

        return val;
    }

    public DERObject toASN1Object()
    {
        if (tag == directoryName)       // directoryName is explicitly tagged as it is a CHOICE
        {
            return new DERTaggedObject(true, tag, obj);
        }
        else
        {
            return new DERTaggedObject(false, tag, obj);
        }
    }
}