A solution to Square's "Square Root" Java puzzler (http://corner.squareup.com/2013/03/puzzle-square-root.html)

EriksNotSecureRandomSpi.java

import square.SquareRoot;

import java.math.BigInteger;
import java.security.Provider;
import java.security.SecureRandomSpi;
import java.security.Security;

/**
 * A Not very secure random provider implementation.
 * Made for Square's "Square Root" Java puzzler (2013/03/19).
 * @author Erik Tjernlund (erik@tjernlund.net)
 */
public class EriksNotSecureRandomSpi extends SecureRandomSpi {

    @Override
    protected void engineSetSeed(byte[] seed) {
    }

    @Override
    protected void engineNextBytes(byte[] bytes) {
        bytes[bytes.length - 1] = 1;
    }

    @Override
    protected byte[] engineGenerateSeed(int numBytes) {
        return new byte[0];
    }
}

/**
 * Security provider that registers an insane secure random algorithm implementation.
 * Made for Square's "Square Root" Java puzzler (2013/03/19).
 * @author Erik Tjernlund (erik@tjernlund.net)
 */
final class EriksSecurityProvider extends Provider {

    public EriksSecurityProvider(String name, double version, String info) {
        super(name, version, info);
        put("SecureRandom.SHA1PRNG", "EriksNotSecureRandomSpi");
    }

    /**
     * Run to solve Square's "Square Root" Java puzzler (2013/03/19).
     */
    public static void main(String[] args) {
        Provider provider = new EriksSecurityProvider("EriksSecurityProvider", 1.0, "Erik's not really very secure security provider");
        Security.insertProviderAt(provider, 1);
        SquareRoot.answer(new BigInteger("1"));
    }

}