package org.bouncycastle.crypto.generators;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.digests.SHA1Digest;
import org.bouncycastle.crypto.digests.SHA256Digest;
import org.bouncycastle.crypto.params.DSAParameters;
import org.bouncycastle.crypto.params.DSAValidationParameters;
import org.bouncycastle.util.Arrays;
import org.bouncycastle.util.BigIntegers;
import java.math.BigInteger;
import java.security.SecureRandom;
// TODO Update javadoc to mention FIPS 186-3 when done
/**
* generate suitable parameters for DSA, in line with FIPS 186-2.
*/
public class DSAParametersGenerator
{
private int L, N;
private int certainty;
private SecureRandom random;
private static final BigInteger ZERO = BigInteger.valueOf(0);
private static final BigInteger ONE = BigInteger.valueOf(1);
private static final BigInteger TWO = BigInteger.valueOf(2);
/**
* initialise the key generator.
*
* @param size size of the key (range 2^512 -> 2^1024 - 64 bit increments)
* @param certainty measure of robustness of prime (for FIPS 186-2 compliance this should be at least 80).
* @param random random byte source.
*/
public void init(
int size,
int certainty,
SecureRandom random)
{
init(size, getDefaultN(size), certainty, random);
}
// TODO Make public to enable support for DSA keys > 1024 bits
private void init(
int L,
int N,
int certainty,
SecureRandom random)
{
// TODO Check that the (L, N) pair is in the list of acceptable (L, N pairs) (see Section 4.2)
// TODO Should we enforce the minimum 'certainty' values as per C.3 Table C.1?
this.L = L;
this.N = N;
this.certainty = certainty;
this.random = random;
}
/**
* which generates the p and g values from the given parameters,
* returning the DSAParameters object.
* <p>
* Note: can take a while...
*/
public DSAParameters generateParameters()
{
return L > 1024
? generateParameters_FIPS186_3()
: generateParameters_FIPS186_2();
}
private DSAParameters generateParameters_FIPS186_2()
{
byte[] seed = new byte[20];
byte[] part1 = new byte[20];
byte[] part2 = new byte[20];
byte[] u = new byte[20];
SHA1Digest sha1 = new SHA1Digest();
int n = (L - 1) / 160;
byte[] w = new byte[L / 8];
for (;;)
{
random.nextBytes(seed);
hash(sha1, seed, part1);
System.arraycopy(seed, 0, part2, 0, seed.length);
inc(part2);
hash(sha1, part2, part2);
for (int i = 0; i != u.length; i++)
{
u[i] = (byte)(part1[i] ^ part2[i]);
}
u[0] |= (byte)0x80;
u[19] |= (byte)0x01;
BigInteger q = new BigInteger(1, u);
if (!q.isProbablePrime(certainty))
{
continue;
}
byte[] offset = Arrays.clone(seed);
inc(offset);
for (int counter = 0; counter < 4096; ++counter)
{
for (int k = 0; k < n; k++)
{
inc(offset);
hash(sha1, offset, part1);
System.arraycopy(part1, 0, w, w.length - (k + 1) * part1.length, part1.length);
}
inc(offset);
hash(sha1, offset, part1);
System.arraycopy(part1, part1.length - ((w.length - (n) * part1.length)), w, 0, w.length - n * part1.length);
w[0] |= (byte)0x80;
BigInteger x = new BigInteger(1, w);
BigInteger c = x.mod(q.shiftLeft(1));
BigInteger p = x.subtract(c.subtract(ONE));
if (p.bitLength() != L)
{
continue;
}
if (p.isProbablePrime(certainty))
{
BigInteger g = calculateGenerator_FIPS186_2(p, q, random);
return new DSAParameters(p, q, g, new DSAValidationParameters(seed, counter));
}
}
}
}
private static BigInteger calculateGenerator_FIPS186_2(BigInteger p, BigInteger q, SecureRandom r)
{
BigInteger e = p.subtract(ONE).divide(q);
BigInteger pSub2 = p.subtract(TWO);
for (;;)
{
BigInteger h = BigIntegers.createRandomInRange(TWO, pSub2, r);
BigInteger g = h.modPow(e, p);
if (g.bitLength() > 1)
{
return g;
}
}
}
/**
* generate suitable parameters for DSA, in line with
* <i>FIPS 186-3 A.1 Generation of the FFC Primes p and q</i>.
*/
private DSAParameters generateParameters_FIPS186_3()
{
// A.1.1.2 Generation of the Probable Primes p and q Using an Approved Hash Function
// FIXME This should be configurable (digest size in bits must be >= N)
Digest d = new SHA256Digest();
int outlen = d.getDigestSize() * 8;
// 1. Check that the (L, N) pair is in the list of acceptable (L, N pairs) (see Section 4.2). If
// the pair is not in the list, then return INVALID.
// Note: checked at initialisation
// 2. If (seedlen < N), then return INVALID.
// FIXME This should be configurable (must be >= N)
int seedlen = N;
byte[] seed = new byte[seedlen / 8];
// 3. n = ceiling(L ⁄ outlen) – 1.
int n = (L - 1) / outlen;
// 4. b = L – 1 – (n ∗ outlen).
int b = (L - 1) % outlen;
byte[] output = new byte[d.getDigestSize()];
for (;;)
{
// 5. Get an arbitrary sequence of seedlen bits as the domain_parameter_seed.
random.nextBytes(seed);
// 6. U = Hash (domain_parameter_seed) mod 2^(N–1).
hash(d, seed, output);
BigInteger U = new BigInteger(1, output).mod(ONE.shiftLeft(N - 1));
// 7. q = 2^(N–1) + U + 1 – ( U mod 2).
BigInteger q = ONE.shiftLeft(N - 1).add(U).add(ONE).subtract(U.mod(TWO));
// 8. Test whether or not q is prime as specified in Appendix C.3.
// TODO Review C.3 for primality checking
if (!q.isProbablePrime(certainty))
{
// 9. If q is not a prime, then go to step 5.
continue;
}
// 10. offset = 1.
// Note: 'offset' value managed incrementally
byte[] offset = Arrays.clone(seed);
// 11. For counter = 0 to (4L – 1) do
int counterLimit = 4 * L;
for (int counter = 0; counter < counterLimit; ++counter)
{
// 11.1 For j = 0 to n do
// Vj = Hash ((domain_parameter_seed + offset + j) mod 2^seedlen).
// 11.2 W = V0 + (V1 ∗ 2^outlen) + ... + (V^(n–1) ∗ 2^((n–1) ∗ outlen)) + ((Vn mod 2^b) ∗ 2^(n ∗ outlen)).
// TODO Assemble w as a byte array
BigInteger W = ZERO;
for (int j = 0, exp = 0; j <= n; ++j, exp += outlen)
{
inc(offset);
hash(d, offset, output);
BigInteger Vj = new BigInteger(1, output);
if (j == n)
{
Vj = Vj.mod(ONE.shiftLeft(b));
}
W = W.add(Vj.shiftLeft(exp));
}
// 11.3 X = W + 2^(L–1). Comment: 0 ≤ W < 2L–1; hence, 2L–1 ≤ X < 2L.
BigInteger X = W.add(ONE.shiftLeft(L - 1));
// 11.4 c = X mod 2q.
BigInteger c = X.mod(q.shiftLeft(1));
// 11.5 p = X - (c - 1). Comment: p ≡ 1 (mod 2q).
BigInteger p = X.subtract(c.subtract(ONE));
// 11.6 If (p < 2^(L - 1)), then go to step 11.9
if (p.bitLength() != L)
{
continue;
}
// 11.7 Test whether or not p is prime as specified in Appendix C.3.
// TODO Review C.3 for primality checking
if (p.isProbablePrime(certainty))
{
// 11.8 If p is determined to be prime, then return VALID and the values of p, q and
// (optionally) the values of domain_parameter_seed and counter.
// TODO Make configurable (8-bit unsigned)?
// int index = 1;
// BigInteger g = calculateGenerator_FIPS186_3_Verifiable(d, p, q, seed, index);
// if (g != null)
// {
// // TODO Should 'index' be a part of the validation parameters?
// return new DSAParameters(p, q, g, new DSAValidationParameters(seed, counter));
// }
BigInteger g = calculateGenerator_FIPS186_3_Unverifiable(p, q, random);
return new DSAParameters(p, q, g, new DSAValidationParameters(seed, counter));
}
// 11.9 offset = offset + n + 1. Comment: Increment offset; then, as part of
// the loop in step 11, increment counter; if
// counter < 4L, repeat steps 11.1 through 11.8.
// Note: 'offset' value already incremented in inner loop
}
// 12. Go to step 5.
}
}
private static BigInteger calculateGenerator_FIPS186_3_Unverifiable(BigInteger p, BigInteger q,
SecureRandom r)
{
return calculateGenerator_FIPS186_2(p, q, r);
}
// private static BigInteger calculateGenerator_FIPS186_3_Verifiable(Digest d, BigInteger p, BigInteger q,
// byte[] seed, int index)
// {
//// A.2.3 Verifiable Canonical Generation of the Generator g
// BigInteger e = p.subtract(ONE).divide(q);
// byte[] ggen = Hex.decode("6767656E");
//
// // 7. U = domain_parameter_seed || "ggen" || index || count.
// byte[] U = new byte[seed.length + ggen.length + 1 + 2];
// System.arraycopy(seed, 0, U, 0, seed.length);
// System.arraycopy(ggen, 0, U, seed.length, ggen.length);
// U[U.length - 3] = (byte)index;
//
// byte[] w = new byte[d.getDigestSize()];
// for (int count = 1; count < (1 << 16); ++count)
// {
// inc(U);
// hash(d, U, w);
// BigInteger W = new BigInteger(1, w);
// BigInteger g = W.modPow(e, p);
// if (g.compareTo(TWO) >= 0)
// {
// return g;
// }
// }
//
// return null;
// }
private static void hash(Digest d, byte[] input, byte[] output)
{
d.update(input, 0, input.length);
d.doFinal(output, 0);
}
private static int getDefaultN(int L)
{
return L > 1024 ? 256 : 160;
}
private static void inc(byte[] buf)
{
for (int i = buf.length - 1; i >= 0; --i)
{
byte b = (byte)((buf[i] + 1) & 0xff);
buf[i] = b;
if (b != 0)
{
break;
}
}
}
}