* Reference: *
n, and e values. The
* default is to generate n and use a fixed value for
* e (Fermat's F4 number).
*/
public static final String RSA_PARAMETERS = "gnu.crypto.rsa.params";
/**
* Property name of the preferred encoding format to use when externalizing
* generated instance of key-pairs from this generator. The property is taken
* to be an {@link Integer} that encapsulates an encoding format identifier.
*/
public static final String PREFERRED_ENCODING_FORMAT = "gnu.crypto.rsa.encoding";
/** Default value for the modulus length. */
private static final int DEFAULT_MODULUS_LENGTH = 1024;
/** Default encoding format to use when none was specified. */
private static final int DEFAULT_ENCODING_FORMAT = Registry.RAW_ENCODING_ID;
/** The desired bit length of the modulus. */
private int L;
/**
* This implementation uses, by default, Fermat's F4 number as the public
* exponent.
*/
private BigInteger e = BigInteger.valueOf(65537L);
/** The optional {@link SecureRandom} instance to use. */
private SecureRandom rnd = null;
/** Our default source of randomness. */
private PRNG prng = null;
/** Preferred encoding format of generated keys. */
private int preferredFormat;
// implicit 0-arguments constructor
public String name()
{
return Registry.RSA_KPG;
}
/**
* Configures this instance.
*
* @param attributes the map of name/value pairs to use.
* @exception IllegalArgumentException if the designated MODULUS_LENGTH value
* is less than 1024.
*/
public void setup(Map attributes)
{
if (Configuration.DEBUG)
log.entering(this.getClass().getName(), "setup", attributes);
// do we have a SecureRandom, or should we use our own?
rnd = (SecureRandom) attributes.get(SOURCE_OF_RANDOMNESS);
// are we given a set of RSA params or we shall use our own?
RSAKeyGenParameterSpec params = (RSAKeyGenParameterSpec) attributes.get(RSA_PARAMETERS);
// find out the modulus length
if (params != null)
{
L = params.getKeysize();
e = params.getPublicExponent();
}
else
{
Integer l = (Integer) attributes.get(MODULUS_LENGTH);
L = (l == null ? DEFAULT_MODULUS_LENGTH : l.intValue());
}
if (L < 1024)
throw new IllegalArgumentException(MODULUS_LENGTH);
// what is the preferred encoding format
Integer formatID = (Integer) attributes.get(PREFERRED_ENCODING_FORMAT);
preferredFormat = formatID == null ? DEFAULT_ENCODING_FORMAT
: formatID.intValue();
if (Configuration.DEBUG)
log.exiting(this.getClass().getName(), "setup");
}
/**
*
* The algorithm used here is described in nessie-pss-B.pdf document
* which is part of the RSA-PSS submission to NESSIE.
*
*
* @return an RSA keypair.
*/
public KeyPair generate()
{
if (Configuration.DEBUG)
log.entering(this.getClass().getName(), "generate");
BigInteger p, q, n, d;
// 1. Generate a prime p in the interval [2**(M-1), 2**M - 1], where
// M = CEILING(L/2), and such that GCD(p, e) = 1
int M = (L + 1) / 2;
BigInteger lower = TWO.pow(M - 1);
BigInteger upper = TWO.pow(M).subtract(ONE);
byte[] kb = new byte[(M + 7) / 8]; // enough bytes to frame M bits
step1: while (true)
{
nextRandomBytes(kb);
p = new BigInteger(1, kb).setBit(0);
if (p.compareTo(lower) >= 0 && p.compareTo(upper) <= 0
&& p.isProbablePrime(80) && p.gcd(e).equals(ONE))
break step1;
}
// 2. Generate a prime q such that the product of p and q is an L-bit
// number, and such that GCD(q, e) = 1
step2: while (true)
{
nextRandomBytes(kb);
q = new BigInteger(1, kb).setBit(0);
n = p.multiply(q);
if (n.bitLength() == L && q.isProbablePrime(80) && q.gcd(e).equals(ONE))
break step2;
// TODO: test for p != q
}
// TODO: ensure p < q
// 3. Put n = pq. The public key is (n, e).
// 4. Compute the parameters necessary for the private key K (see
// Section 2.2).
BigInteger phi = p.subtract(ONE).multiply(q.subtract(ONE));
d = e.modInverse(phi);
// 5. Output the public key and the private key.
PublicKey pubK = new GnuRSAPublicKey(preferredFormat, n, e);
PrivateKey secK = new GnuRSAPrivateKey(preferredFormat, p, q, e, d);
KeyPair result = new KeyPair(pubK, secK);
if (Configuration.DEBUG)
log.exiting(this.getClass().getName(), "generate", result);
return result;
}
/**
* Fills the designated byte array with random data.
*
* @param buffer the byte array to fill with random data.
*/
private void nextRandomBytes(byte[] buffer)
{
if (rnd != null)
rnd.nextBytes(buffer);
else
getDefaultPRNG().nextBytes(buffer);
}
private PRNG getDefaultPRNG()
{
if (prng == null)
prng = PRNG.getInstance();
return prng;
}
}