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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 1.4.

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package org.bouncycastle.asn1.x9;

import java.math.BigInteger;

import org.bouncycastle.asn1.ASN1Object;
import org.bouncycastle.asn1.ASN1OctetString;
import org.bouncycastle.asn1.ASN1Primitive;
import org.bouncycastle.asn1.DEROctetString;
import org.bouncycastle.math.ec.ECFieldElement;

/**
 * class for processing an FieldElement as a DER object.
 */
public class X9FieldElement
    extends ASN1Object
{
    protected ECFieldElement  f;
    
    private static X9IntegerConverter converter = new X9IntegerConverter();

    public X9FieldElement(ECFieldElement f)
    {
        this.f = f;
    }
    
    public X9FieldElement(BigInteger p, ASN1OctetString s)
    {
        this(new ECFieldElement.Fp(p, new BigInteger(1, s.getOctets())));
    }
    
    public X9FieldElement(int m, int k1, int k2, int k3, ASN1OctetString s)
    {
        this(new ECFieldElement.F2m(m, k1, k2, k3, new BigInteger(1, s.getOctets())));
    }
    
    public ECFieldElement getValue()
    {
        return f;
    }
    
    /**
     * Produce an object suitable for an ASN1OutputStream.
     *  
     *  FieldElement ::= OCTET STRING
     *

* * if q is an odd prime then the field element is * processed as an Integer and converted to an octet string * according to x 9.62 4.3.1. * if q is 2 m then the bit string * contained in the field element is converted into an octet * string with the same ordering padded at the front if necessary. * * */ public ASN1Primitive toASN1Primitive() { int byteCount = converter.getByteLength(f); byte[] paddedBigInteger = converter.integerToBytes(f.toBigInteger(), byteCount); return new DEROctetString(paddedBigInteger); } }