org.bouncycastle.asn1.x9.X9IntegerConverter.java Source code

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Here is the source code for org.bouncycastle.asn1.x9.X9IntegerConverter.java

Source

package org.bouncycastle.asn1.x9;

import java.math.BigInteger;

import org.bouncycastle.math.ec.ECCurve;
import org.bouncycastle.math.ec.ECFieldElement;

/**
 * A class which converts integers to byte arrays, allowing padding and calculations
 * to be done according the the filed size of the curve or field element involved.
 */
public class X9IntegerConverter {
    /**
     * Return the curve's field size in bytes.
     *
     * @param c the curve of interest.
     * @return the field size in bytes (rounded up).
     */
    public int getByteLength(ECCurve c) {
        return (c.getFieldSize() + 7) / 8;
    }

    /**
     * Return the field element's field size in bytes.
     *
     * @param fe the field element of interest.
     * @return the field size in bytes (rounded up).
     */
    public int getByteLength(ECFieldElement fe) {
        return (fe.getFieldSize() + 7) / 8;
    }

    /**
     * Convert an integer to a byte array, ensuring it is exactly qLength long.
     *
     * @param s the integer to be converted.
     * @param qLength the length
     * @return the resulting byte array.
     */
    public byte[] integerToBytes(BigInteger s, int qLength) {
        byte[] bytes = s.toByteArray();

        if (qLength < bytes.length) {
            byte[] tmp = new byte[qLength];

            System.arraycopy(bytes, bytes.length - tmp.length, tmp, 0, tmp.length);

            return tmp;
        } else if (qLength > bytes.length) {
            byte[] tmp = new byte[qLength];

            System.arraycopy(bytes, 0, tmp, tmp.length - bytes.length, bytes.length);

            return tmp;
        }

        return bytes;
    }
}