1 files changed, 66 insertions, 0 deletions
diff --git a/comm/third_party/botan/src/lib/pubkey/workfactor.cpp b/comm/third_party/botan/src/lib/pubkey/workfactor.cpp
new file mode 100644
index 0000000000..bb4fd56ca5
--- /dev/null
+++ b/comm/third_party/botan/src/lib/pubkey/workfactor.cpp
@@ -0,0 +1,66 @@
+/*
+* Public Key Work Factor Functions
+* (C) 1999-2007,2012 Jack Lloyd
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#include <botan/workfactor.h>
+#include <algorithm>
+#include <cmath>
+
+namespace Botan {
+
+size_t ecp_work_factor(size_t bits)
+   {
+   return bits / 2;
+   }
+
+namespace {
+
+size_t nfs_workfactor(size_t bits, double log2_k)
+   {
+   // approximates natural logarithm of an integer of given bitsize
+   const double log2_e = 1.44269504088896340736;
+   const double log_p = bits / log2_e;
+
+   const double log_log_p = std::log(log_p);
+
+   // RFC 3766: k * e^((1.92 + o(1)) * cubrt(ln(n) * (ln(ln(n)))^2))
+   const double est = 1.92 * std::pow(log_p * log_log_p * log_log_p, 1.0/3.0);
+
+   // return log2 of the workfactor
+   return static_cast<size_t>(log2_k + log2_e * est);
+   }
+
+}
+
+size_t if_work_factor(size_t bits)
+   {
+   // RFC 3766 estimates k at .02 and o(1) to be effectively zero for sizes of interest
+
+   const double log2_k = -5.6438; // log2(.02)
+   return nfs_workfactor(bits, log2_k);
+   }
+
+size_t dl_work_factor(size_t bits)
+   {
+   // Lacking better estimates...
+   return if_work_factor(bits);
+   }
+
+size_t dl_exponent_size(size_t bits)
+   {
+   /*
+   This uses a slightly tweaked version of the standard work factor
+   function above. It assumes k is 1 (thus overestimating the strength
+   of the prime group by 5-6 bits), and always returns at least 128 bits
+   (this only matters for very small primes).
+   */
+   const size_t min_workfactor = 64;
+   const double log2_k = 0;
+
+   return 2 * std::max<size_t>(min_workfactor, nfs_workfactor(bits, log2_k));
+   }
+
+}