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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
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package sun.security.rsa;
import java.math.BigInteger;
import java.security.*;
import java.security.spec.AlgorithmParameterSpec;
import java.security.spec.RSAKeyGenParameterSpec;
import sun.security.jca.JCAUtil;
/**
* RSA keypair generation. Standard algorithm, minimum key length 512 bit.
* We generate two random primes until we find two where phi is relative
* prime to the public exponent. Default exponent is 65537. It has only bit 0
* and bit 4 set, which makes it particularly efficient.
*
* @since 1.5
* @author Andreas Sterbenz
*/
public final class RSAKeyPairGenerator extends KeyPairGeneratorSpi {
// public exponent to use
private BigInteger publicExponent;
// size of the key to generate, >= RSAKeyFactory.MIN_MODLEN
private int keySize;
// PRNG to use
private SecureRandom random;
public RSAKeyPairGenerator() {
// initialize to default in case the app does not call initialize()
initialize(1024, null);
}
// initialize the generator. See JCA doc
public void initialize(int keySize, SecureRandom random) {
// do not allow unreasonably small or large key sizes,
// probably user error
try {
RSAKeyFactory.checkKeyLengths(keySize, RSAKeyGenParameterSpec.F4,
512, 64 * 1024);
} catch (InvalidKeyException e) {
throw new InvalidParameterException(e.getMessage());
}
this.keySize = keySize;
this.random = random;
this.publicExponent = RSAKeyGenParameterSpec.F4;
}
// second initialize method. See JCA doc.
public void initialize(AlgorithmParameterSpec params, SecureRandom random)
throws InvalidAlgorithmParameterException {
if (params instanceof RSAKeyGenParameterSpec == false) {
throw new InvalidAlgorithmParameterException
("Params must be instance of RSAKeyGenParameterSpec");
}
RSAKeyGenParameterSpec rsaSpec = (RSAKeyGenParameterSpec)params;
int tmpKeySize = rsaSpec.getKeysize();
BigInteger tmpPublicExponent = rsaSpec.getPublicExponent();
if (tmpPublicExponent == null) {
tmpPublicExponent = RSAKeyGenParameterSpec.F4;
} else {
if (tmpPublicExponent.compareTo(RSAKeyGenParameterSpec.F0) < 0) {
throw new InvalidAlgorithmParameterException
("Public exponent must be 3 or larger");
}
if (tmpPublicExponent.bitLength() > tmpKeySize) {
throw new InvalidAlgorithmParameterException
("Public exponent must be smaller than key size");
}
}
// do not allow unreasonably large key sizes, probably user error
try {
RSAKeyFactory.checkKeyLengths(tmpKeySize, tmpPublicExponent,
512, 64 * 1024);
} catch (InvalidKeyException e) {
throw new InvalidAlgorithmParameterException(
"Invalid key sizes", e);
}
this.keySize = tmpKeySize;
this.publicExponent = tmpPublicExponent;
this.random = random;
}
// generate the keypair. See JCA doc
public KeyPair generateKeyPair() {
// accomodate odd key sizes in case anybody wants to use them
int lp = (keySize + 1) >> 1;
int lq = keySize - lp;
if (random == null) {
random = JCAUtil.getSecureRandom();
}
BigInteger e = publicExponent;
while (true) {
// generate two random primes of size lp/lq
BigInteger p = BigInteger.probablePrime(lp, random);
BigInteger q, n;
do {
q = BigInteger.probablePrime(lq, random);
// convention is for p > q
if (p.compareTo(q) < 0) {
BigInteger tmp = p;
p = q;
q = tmp;
}
// modulus n = p * q
n = p.multiply(q);
// even with correctly sized p and q, there is a chance that
// n will be one bit short. re-generate the smaller prime if so
} while (n.bitLength() < keySize);
// phi = (p - 1) * (q - 1) must be relative prime to e
// otherwise RSA just won't work ;-)
BigInteger p1 = p.subtract(BigInteger.ONE);
BigInteger q1 = q.subtract(BigInteger.ONE);
BigInteger phi = p1.multiply(q1);
// generate new p and q until they work. typically
// the first try will succeed when using F4
if (e.gcd(phi).equals(BigInteger.ONE) == false) {
continue;
}
// private exponent d is the inverse of e mod phi
BigInteger d = e.modInverse(phi);
// 1st prime exponent pe = d mod (p - 1)
BigInteger pe = d.mod(p1);
// 2nd prime exponent qe = d mod (q - 1)
BigInteger qe = d.mod(q1);
// crt coefficient coeff is the inverse of q mod p
BigInteger coeff = q.modInverse(p);
try {
PublicKey publicKey = new RSAPublicKeyImpl(n, e);
PrivateKey privateKey =
new RSAPrivateCrtKeyImpl(n, e, d, p, q, pe, qe, coeff);
return new KeyPair(publicKey, privateKey);
} catch (InvalidKeyException exc) {
// invalid key exception only thrown for keys < 512 bit,
// will not happen here
throw new RuntimeException(exc);
}
}
}
}
