bcprov/src/main/java/org/bouncycastle/pqc/crypto/rainbow/Layer.java

package org.bouncycastle.pqc.crypto.rainbow;

import java.security.SecureRandom;

import org.bouncycastle.pqc.crypto.rainbow.util.GF2Field;
import org.bouncycastle.pqc.crypto.rainbow.util.RainbowUtil;
import org.bouncycastle.util.Arrays;


/**
 * This class represents a layer of the Rainbow Oil- and Vinegar Map. Each Layer
 * consists of oi polynomials with their coefficients, generated at random.
 * <p>
 * To sign a document, we solve a LES (linear equation system) for each layer in
 * order to find the oil variables of that layer and to be able to use the
 * variables to compute the signature. This functionality is implemented in the
 * RainbowSignature-class, by the aid of the private key.
 * <p>
 * Each layer is a part of the private key.
 * <p>
 * More information about the layer can be found in the paper of Jintai Ding,
 * Dieter Schmidt: Rainbow, a New Multivariable Polynomial Signature Scheme.
 * ACNS 2005: 164-175 (http://dx.doi.org/10.1007/11496137_12)
 */
public class Layer
{
    private int vi; // number of vinegars in this layer
    private int viNext; // number of vinegars in next layer
    private int oi; // number of oils in this layer

    /*
      * k : index of polynomial
      *
      * i,j : indices of oil and vinegar variables
      */
    private short[/* k */][/* i */][/* j */] coeff_alpha;
    private short[/* k */][/* i */][/* j */] coeff_beta;
    private short[/* k */][/* i */] coeff_gamma;
    private short[/* k */] coeff_eta;

    /**
     * Constructor
     *
     * @param vi         number of vinegar variables of this layer
     * @param viNext     number of vinegar variables of next layer. It's the same as
     *                   (num of oils) + (num of vinegars) of this layer.
     * @param coeffAlpha alpha-coefficients in the polynomials of this layer
     * @param coeffBeta  beta-coefficients in the polynomials of this layer
     * @param coeffGamma gamma-coefficients in the polynomials of this layer
     * @param coeffEta   eta-coefficients in the polynomials of this layer
     */
    public Layer(byte vi, byte viNext, short[][][] coeffAlpha,
                 short[][][] coeffBeta, short[][] coeffGamma, short[] coeffEta)
    {
        this.vi = vi & 0xff;
        this.viNext = viNext & 0xff;
        this.oi = this.viNext - this.vi;

        // the secret coefficients of all polynomials in this layer
        this.coeff_alpha = coeffAlpha;
        this.coeff_beta = coeffBeta;
        this.coeff_gamma = coeffGamma;
        this.coeff_eta = coeffEta;
    }

    /**
     * This function generates the coefficients of all polynomials in this layer
     * at random using random generator.
     *
     * @param sr the random generator which is to be used
     */
    public Layer(int vi, int viNext, SecureRandom sr)
    {
        this.vi = vi;
        this.viNext = viNext;
        this.oi = viNext - vi;

        // the coefficients of all polynomials in this layer
        this.coeff_alpha = new short[this.oi][this.oi][this.vi];
        this.coeff_beta = new short[this.oi][this.vi][this.vi];
        this.coeff_gamma = new short[this.oi][this.viNext];
        this.coeff_eta = new short[this.oi];

        int numOfPoly = this.oi; // number of polynomials per layer

        // Alpha coeffs
        for (int k = 0; k < numOfPoly; k++)
        {
            for (int i = 0; i < this.oi; i++)
            {
                for (int j = 0; j < this.vi; j++)
                {
                    coeff_alpha[k][i][j] = (short)(sr.nextInt() & GF2Field.MASK);
                }
            }
        }
        // Beta coeffs
        for (int k = 0; k < numOfPoly; k++)
        {
            for (int i = 0; i < this.vi; i++)
            {
                for (int j = 0; j < this.vi; j++)
                {
                    coeff_beta[k][i][j] = (short)(sr.nextInt() & GF2Field.MASK);
                }
            }
        }
        // Gamma coeffs
        for (int k = 0; k < numOfPoly; k++)
        {
            for (int i = 0; i < this.viNext; i++)
            {
                coeff_gamma[k][i] = (short)(sr.nextInt() & GF2Field.MASK);
            }
        }
        // Eta
        for (int k = 0; k < numOfPoly; k++)
        {
            coeff_eta[k] = (short)(sr.nextInt() & GF2Field.MASK);
        }
    }

    /**
     * This method plugs in the vinegar variables into the polynomials of this
     * layer and computes the coefficients of the Oil-variables as well as the
     * free coefficient in each polynomial.
     * <p>
     * It is needed for computing the Oil variables while signing.
     *
     * @param x vinegar variables of this layer that should be plugged into
     *          the polynomials.
     * @return coeff the coefficients of Oil variables and the free coeff in the
     *         polynomials of this layer.
     */
    public short[][] plugInVinegars(short[] x)
    {
        // temporary variable needed for the multiplication
        short tmpMult = 0;
        // coeff: 1st index = which polynomial, 2nd index=which variable
        short[][] coeff = new short[oi][oi + 1]; // gets returned
        // free coefficient per polynomial
        short[] sum = new short[oi];

        /*
           * evaluate the beta-part of the polynomials (it contains no oil
           * variables)
           */
        for (int k = 0; k < oi; k++)
        {
            for (int i = 0; i < vi; i++)
            {
                for (int j = 0; j < vi; j++)
                {
                    // tmp = beta * xi (plug in)
                    tmpMult = GF2Field.multElem(coeff_beta[k][i][j], x[i]);
                    // tmp = tmp * xj
                    tmpMult = GF2Field.multElem(tmpMult, x[j]);
                    // accumulate into the array for the free coefficients.
                    sum[k] = GF2Field.addElem(sum[k], tmpMult);
                }
            }
        }

        /* evaluate the alpha-part (it contains oils) */
        for (int k = 0; k < oi; k++)
        {
            for (int i = 0; i < oi; i++)
            {
                for (int j = 0; j < vi; j++)
                {
                    // alpha * xj (plug in)
                    tmpMult = GF2Field.multElem(coeff_alpha[k][i][j], x[j]);
                    // accumulate
                    coeff[k][i] = GF2Field.addElem(coeff[k][i], tmpMult);
                }
            }
        }
        /* evaluate the gama-part of the polynomial (containing no oils) */
        for (int k = 0; k < oi; k++)
        {
            for (int i = 0; i < vi; i++)
            {
                // gamma * xi (plug in)
                tmpMult = GF2Field.multElem(coeff_gamma[k][i], x[i]);
                // accumulate in the array for the free coefficients (per
                // polynomial).
                sum[k] = GF2Field.addElem(sum[k], tmpMult);
            }
        }
        /* evaluate the gama-part of the polynomial (but containing oils) */
        for (int k = 0; k < oi; k++)
        {
            for (int i = vi; i < viNext; i++)
            { // oils
                // accumulate the coefficients of the oil variables (per
                // polynomial).
                coeff[k][i - vi] = GF2Field.addElem(coeff_gamma[k][i],
                    coeff[k][i - vi]);
            }
        }
        /* evaluate the eta-part of the polynomial */
        for (int k = 0; k < oi; k++)
        {
            // accumulate in the array for the free coefficients per polynomial.
            sum[k] = GF2Field.addElem(sum[k], coeff_eta[k]);
        }

        /* put the free coefficients (sum) into the coeff-array as last column */
        for (int k = 0; k < oi; k++)
        {
            coeff[k][oi] = sum[k];
        }
        return coeff;
    }

    /**
     * Getter for the number of vinegar variables of this layer.
     *
     * @return the number of vinegar variables of this layer.
     */
    public int getVi()
    {
        return vi;
    }

    /**
     * Getter for the number of vinegar variables of the next layer.
     *
     * @return the number of vinegar variables of the next layer.
     */
    public int getViNext()
    {
        return viNext;
    }

    /**
     * Getter for the number of Oil variables of this layer.
     *
     * @return the number of oil variables of this layer.
     */
    public int getOi()
    {
        return oi;
    }

    /**
     * Getter for the alpha-coefficients of the polynomials in this layer.
     *
     * @return the coefficients of alpha-terms of this layer.
     */
    public short[][][] getCoeffAlpha()
    {
        return coeff_alpha;
    }

    /**
     * Getter for the beta-coefficients of the polynomials in this layer.
     *
     * @return the coefficients of beta-terms of this layer.
     */

    public short[][][] getCoeffBeta()
    {
        return coeff_beta;
    }

    /**
     * Getter for the gamma-coefficients of the polynomials in this layer.
     *
     * @return the coefficients of gamma-terms of this layer
     */
    public short[][] getCoeffGamma()
    {
        return coeff_gamma;
    }

    /**
     * Getter for the eta-coefficients of the polynomials in this layer.
     *
     * @return the coefficients eta of this layer
     */
    public short[] getCoeffEta()
    {
        return coeff_eta;
    }

    /**
     * This function compares this Layer with another object.
     *
     * @param other the other object
     * @return the result of the comparison
     */
    public boolean equals(Object other)
    {
        if (other == null || !(other instanceof Layer))
        {
            return false;
        }
        Layer otherLayer = (Layer)other;

        return  vi == otherLayer.getVi()
                && viNext == otherLayer.getViNext()
                && oi == otherLayer.getOi()
                && RainbowUtil.equals(coeff_alpha, otherLayer.getCoeffAlpha())
                && RainbowUtil.equals(coeff_beta, otherLayer.getCoeffBeta())
                && RainbowUtil.equals(coeff_gamma, otherLayer.getCoeffGamma())
                && RainbowUtil.equals(coeff_eta, otherLayer.getCoeffEta());
    }

    public int hashCode()
    {
        int hash = vi;
        hash = hash * 37 + viNext;
        hash = hash * 37 + oi;
        hash = hash * 37 + Arrays.hashCode(coeff_alpha);
        hash = hash * 37 + Arrays.hashCode(coeff_beta);
        hash = hash * 37 + Arrays.hashCode(coeff_gamma);
        hash = hash * 37 + Arrays.hashCode(coeff_eta);

        return hash;
    }
}