diff options
Diffstat (limited to 'crypto/src/math')
| -rw-r--r-- | crypto/src/math/Primes.cs | 282 |
1 files changed, 282 insertions, 0 deletions
diff --git a/crypto/src/math/Primes.cs b/crypto/src/math/Primes.cs new file mode 100644 index 000000000..dda81b988 --- /dev/null +++ b/crypto/src/math/Primes.cs @@ -0,0 +1,282 @@ +using System; + +using Org.BouncyCastle.Crypto; +using Org.BouncyCastle.Utilities; + +namespace Org.BouncyCastle.Math +{ + public static class Primes + { + private static readonly BigInteger One = BigInteger.One; + private static readonly BigInteger Two = BigInteger.Two; + private static readonly BigInteger Three = BigInteger.Three; + + /** + * Used to return the output from the {@linkplain #generateSTRandomPrime(Digest) Shawe-Taylor Random_Prime Routine} + */ + public class STOutput + { + private readonly BigInteger mPrime; + private readonly byte[] mPrimeSeed; + private readonly int mPrimeGenCounter; + + internal STOutput(BigInteger prime, byte[] primeSeed, int primeGenCounter) + { + this.mPrime = prime; + this.mPrimeSeed = primeSeed; + this.mPrimeGenCounter = primeGenCounter; + } + + public BigInteger Prime + { + get { return mPrime; } + } + + public byte[] PrimeSeed + { + get { return mPrimeSeed; } + } + + public int PrimeGenCounter + { + get { return mPrimeGenCounter; } + } + } + + /** + * FIPS 186-4 C.6 Shawe-Taylor Random_Prime Routine + * + * Construct a provable prime number using a hash function. + * + * @param hash + * the {@link Digest} instance to use (as "Hash()"). Cannot be null. + * @param length + * the length (in bits) of the prime to be generated. Must be >= 2. + * @param inputSeed + * the seed to be used for the generation of the requested prime. Cannot be null or + * empty. + * @returns an {@link STOutput} instance containing the requested prime. + */ + public static STOutput GenerateSTRandomPrime(IDigest hash, int length, byte[] inputSeed) + { + if (hash == null) + throw new ArgumentNullException("hash"); + if (length < 2) + throw new ArgumentException("must be >= 2", "length"); + if (inputSeed == null) + throw new ArgumentNullException("inputSeed"); + if (inputSeed.Length == 0) + throw new ArgumentException("cannot be empty", "inputSeed"); + + return ImplSTRandomPrime(hash, length, Arrays.Clone(inputSeed)); + } + + private static STOutput ImplSTRandomPrime(IDigest d, int length, byte[] primeSeed) + { + int dLen = d.GetDigestSize(); + + if (length < 33) + { + int primeGenCounter = 0; + + byte[] c0 = new byte[dLen]; + byte[] c1 = new byte[dLen]; + + for (;;) + { + Hash(d, primeSeed, c0, 0); + Inc(primeSeed, 1); + + Hash(d, primeSeed, c1, 0); + Inc(primeSeed, 1); + + uint c = Extract32(c0) ^ Extract32(c1); + c &= (uint.MaxValue >> (32 - length)); + c |= (1U << (length - 1)) | 1U; + + ++primeGenCounter; + + if (IsPrime32(c)) + { + return new STOutput(BigInteger.ValueOf((long)c), primeSeed, primeGenCounter); + } + + if (primeGenCounter > (4 * length)) + { + throw new InvalidOperationException("Too many iterations in Shawe-Taylor Random_Prime Routine"); + } + } + } + + STOutput rec = ImplSTRandomPrime(d, (length + 3)/2, primeSeed); + + { + BigInteger c0 = rec.Prime; + primeSeed = rec.PrimeSeed; + int primeGenCounter = rec.PrimeGenCounter; + + int outlen = 8 * dLen; + int iterations = (length - 1)/outlen; + + int oldCounter = primeGenCounter; + + BigInteger x = HashGen(d, primeSeed, iterations + 1); + x = x.Mod(One.ShiftLeft(length - 1)).SetBit(length - 1); + + BigInteger c0x2 = c0.ShiftLeft(1); + BigInteger t = x.Subtract(One).Divide(c0x2).Add(One); + + BigInteger c = t.Multiply(c0x2).Add(One); + + for (;;) + { + if (c.BitLength > length) + { + t = One.ShiftLeft(length - 1).Subtract(One).Divide(c0x2).Add(One); + c = t.Multiply(c0x2).Add(One); + } + + ++primeGenCounter; + + /* + * This is an optimization of the original algorithm, using trial division to screen out + * many non-primes quickly. + * + * NOTE: 'primeSeed' is still incremented as if we performed the full check! + */ + if (MightBePrime(c)) + { + BigInteger a = HashGen(d, primeSeed, iterations + 1); + a = a.Mod(c.Subtract(Three)).Add(Two); + + BigInteger z = a.ModPow(t.ShiftLeft(1), c); + + if (c.Gcd(z.Subtract(One)).Equals(One) && z.ModPow(c0, c).Equals(One)) + { + return new STOutput(c, primeSeed, primeGenCounter); + } + } + else + { + Inc(primeSeed, iterations + 1); + } + + if (primeGenCounter >= ((4 * length) + oldCounter)) + { + throw new InvalidOperationException("Too many iterations in Shawe-Taylor Random_Prime Routine"); + } + + t = t.Add(One); + c = c.Add(c0x2); + } + } + } + + private static uint Extract32(byte[] bs) + { + uint result = 0; + + int count = System.Math.Min(4, bs.Length); + for (int i = 0; i < count; ++i) + { + uint b = bs[bs.Length - (i + 1)]; + result |= (b << (8 * i)); + } + + return result; + } + + private static void Hash(IDigest d, byte[] input, byte[] output, int outPos) + { + d.BlockUpdate(input, 0, input.Length); + d.DoFinal(output, outPos); + } + + private static BigInteger HashGen(IDigest d, byte[] seed, int count) + { + int dLen = d.GetDigestSize(); + int pos = count * dLen; + byte[] buf = new byte[pos]; + for (int i = 0; i < count; ++i) + { + pos -= dLen; + Hash(d, seed, buf, pos); + Inc(seed, 1); + } + return new BigInteger(1, buf); + } + + private static void Inc(byte[] seed, int c) + { + int pos = seed.Length; + while (c > 0 && --pos >= 0) + { + c += seed[pos]; + seed[pos] = (byte)c; + c >>= 8; + } + } + + private static bool IsPrime32(uint x) + { + /* + * Use wheel factorization with 2, 3, 5 to select trial divisors. + */ + + if (x <= 5) + { + return x == 2 || x == 3 || x == 5; + } + + if ((x & 1) == 0 || (x % 3) == 0 || (x % 5) == 0) + { + return false; + } + + uint[] ds = new uint[]{ 1, 7, 11, 13, 17, 19, 23, 29 }; + uint b = 0; + for (int pos = 1; ; pos = 0) + { + /* + * Trial division by wheel-selected divisors + */ + while (pos < ds.Length) + { + uint d = b + ds[pos]; + if (x % d == 0) + { + return x < 30; + } + ++pos; + } + + b += 30; + + if ((b >> 16 != 0) || (b * b >= x)) + { + return true; + } + } + } + + private static bool MightBePrime(BigInteger x) + { + /* + * Bundle trial divisors into ~32-bit moduli then use fast tests on the ~32-bit remainders. + */ + int m0 = 2 * 3 * 5 * 7 * 11 * 13 * 17 * 19 * 23; + int r0 = x.Mod(BigInteger.ValueOf(m0)).IntValue; + if ((r0 & 1) != 0 && (r0 % 3) != 0 && (r0 % 5) != 0 && (r0 % 7) != 0 && (r0 % 11) != 0 + && (r0 % 13) != 0 && (r0 % 17) != 0 && (r0 % 19) != 0 && (r0 % 23) != 0) + { + int m1 = 29 * 31 * 37 * 41 * 43; + int r1 = x.Mod(BigInteger.ValueOf(m1)).IntValue; + if ((r1 % 29) != 0 && (r1 % 31) != 0 && (r1 % 37) != 0 && (r1 % 41) != 0 && (r1 % 43) != 0) + { + return true; + } + } + return false; + } + } +} |