1 files changed, 134 insertions, 0 deletions
diff --git a/lib/math/numbertheory/dsa_gen.cpp b/lib/math/numbertheory/dsa_gen.cpp
new file mode 100644
index 000000000..d30a08f1a
--- /dev/null
+++ b/lib/math/numbertheory/dsa_gen.cpp
@@ -0,0 +1,134 @@
+/*
+* DSA Parameter Generation
+* (C) 1999-2007 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/numthry.h>
+#include <botan/algo_factory.h>
+#include <botan/hash.h>
+#include <botan/parsing.h>
+#include <algorithm>
+#include <memory>
+
+namespace Botan {
+
+namespace {
+
+/*
+* Check if this size is allowed by FIPS 186-3
+*/
+bool fips186_3_valid_size(size_t pbits, size_t qbits)
+   {
+   if(qbits == 160)
+      return (pbits == 512 || pbits == 768 || pbits == 1024);
+
+   if(qbits == 224)
+      return (pbits == 2048);
+
+   if(qbits == 256)
+      return (pbits == 2048 || pbits == 3072);
+
+   return false;
+   }
+
+}
+
+/*
+* Attempt DSA prime generation with given seed
+*/
+bool generate_dsa_primes(RandomNumberGenerator& rng,
+                         Algorithm_Factory& af,
+                         BigInt& p, BigInt& q,
+                         size_t pbits, size_t qbits,
+                         const std::vector<byte>& seed_c)
+   {
+   if(!fips186_3_valid_size(pbits, qbits))
+      throw Invalid_Argument(
+         "FIPS 186-3 does not allow DSA domain parameters of " +
+         std::to_string(pbits) + "/" + std::to_string(qbits) + " bits long");
+
+   if(seed_c.size() * 8 < qbits)
+      throw Invalid_Argument(
+         "Generating a DSA parameter set with a " + std::to_string(qbits) +
+         "long q requires a seed at least as many bits long");
+
+   std::unique_ptr<HashFunction> hash(
+      af.make_hash_function("SHA-" + std::to_string(qbits)));
+
+   const size_t HASH_SIZE = hash->output_length();
+
+   class Seed
+      {
+      public:
+         Seed(const std::vector<byte>& s) : seed(s) {}
+
+         operator std::vector<byte>& () { return seed; }
+
+         Seed& operator++()
+            {
+            for(size_t j = seed.size(); j > 0; --j)
+               if(++seed[j-1])
+                  break;
+            return (*this);
+            }
+      private:
+         std::vector<byte> seed;
+      };
+
+   Seed seed(seed_c);
+
+   q.binary_decode(hash->process(seed));
+   q.set_bit(qbits-1);
+   q.set_bit(0);
+
+   if(!check_prime(q, rng))
+      return false;
+
+   const size_t n = (pbits-1) / (HASH_SIZE * 8),
+                b = (pbits-1) % (HASH_SIZE * 8);
+
+   BigInt X;
+   std::vector<byte> V(HASH_SIZE * (n+1));
+
+   for(size_t j = 0; j != 4096; ++j)
+      {
+      for(size_t k = 0; k <= n; ++k)
+         {
+         ++seed;
+         hash->update(seed);
+         hash->final(&V[HASH_SIZE * (n-k)]);
+         }
+
+      X.binary_decode(&V[HASH_SIZE - 1 - b/8],
+                      V.size() - (HASH_SIZE - 1 - b/8));
+      X.set_bit(pbits-1);
+
+      p = X - (X % (2*q) - 1);
+
+      if(p.bits() == pbits && check_prime(p, rng))
+         return true;
+      }
+   return false;
+   }
+
+/*
+* Generate DSA Primes
+*/
+std::vector<byte> generate_dsa_primes(RandomNumberGenerator& rng,
+                                      Algorithm_Factory& af,
+                                      BigInt& p, BigInt& q,
+                                      size_t pbits, size_t qbits)
+   {
+   while(true)
+      {
+      std::vector<byte> seed(qbits / 8);
+      rng.randomize(&seed[0], seed.size());
+
+      if(generate_dsa_primes(rng, af, p, q, pbits, qbits, seed))
+         return seed;
+      }
+   }
+
+}