Add new PBKDF interface that takes a std::chrono::milliseconds and

runs the KDF until at least that much time has passed, then returns
the number of interations used.

New parameter to the PKCS8 encryption routines which tells how long to
run the PBKDF. Defaults to 200 milliseconds, which is short enough
that it is unlikely to bother anyone but long enough to provide quite
reasonable security against cracking attacks.  On a Core i7-860, 200
ms with PBKDF2/SHA-1 runs about 180K to 220K iterations (compare with
previous default of 10K).

New PBE interface, remove new_params/set_key and require all inputs
including the passphrase to be passed to the constructor.

Drop the PGP S2K as it is pretty weird and not really useful outside
of a full PGP implementation.

Drop the deprecated PKCS8::encrypt_key and PKCS8::encode functions.

1 files changed, 55 insertions, 12 deletions

diff --git a/src/pbkdf/pbkdf2/pbkdf2.cpp b/src/pbkdf/pbkdf2/pbkdf2.cpp
index 699ce7c6b..c116b10ab 100644
--- a/src/pbkdf/pbkdf2/pbkdf2.cpp
+++ b/src/pbkdf/pbkdf2/pbkdf2.cpp
@@ -8,19 +8,22 @@
 #include <botan/pbkdf2.h>
 #include <botan/get_byte.h>
 #include <botan/internal/xor_buf.h>
+#include <botan/internal/rounding.h>
 
 namespace Botan {
 
 /*
 * Return a PKCS #5 PBKDF2 derived key
 */
-OctetString PKCS5_PBKDF2::derive_key(size_t key_len,
-                                     const std::string& passphrase,
-                                     const byte salt[], size_t salt_size,
-                                     size_t iterations) const
+std::pair<size_t, OctetString>
+PKCS5_PBKDF2::key_derivation(size_t key_len,
+                             const std::string& passphrase,
+                             const byte salt[], size_t salt_len,
+                             size_t iterations,
+                             std::chrono::milliseconds msec) const
    {
-   if(iterations == 0)
-      throw Invalid_Argument("PKCS#5 PBKDF2: Invalid iteration count");
+   if(key_len == 0)
+      return std::make_pair(iterations, OctetString());
 
    try
       {
@@ -39,22 +42,62 @@ OctetString PKCS5_PBKDF2::derive_key(size_t key_len,
 
    secure_vector<byte> U(mac->output_length());
 
+   const size_t blocks_needed = round_up(key_len, mac->output_length()) / mac->output_length();
+
+   std::chrono::microseconds usec_per_block =
+      std::chrono::duration_cast<std::chrono::microseconds>(msec) / blocks_needed;
+
    u32bit counter = 1;
    while(key_len)
       {
       size_t T_size = std::min<size_t>(mac->output_length(), key_len);
 
-      mac->update(salt, salt_size);
+      mac->update(salt, salt_len);
       mac->update_be(counter);
       mac->final(&U[0]);
 
       xor_buf(T, &U[0], T_size);
 
-      for(size_t j = 1; j != iterations; ++j)
+      if(iterations == 0)
+         {
+         /*
+         If no iterations set, run the first block to calibrate based
+         on how long hashing takes on whatever machine we're running on.
+         */
+
+         const auto start = std::chrono::high_resolution_clock::now();
+
+         iterations = 1; // the first iteration we did above
+
+         while(true)
+            {
+            mac->update(U);
+            mac->final(&U[0]);
+            xor_buf(T, &U[0], T_size);
+            iterations++;
+
+            /*
+            Only break on relatively 'even' iterations. For one it
+            avoids confusion, and likely some broken implementations
+            break on getting completely randomly distributed values
+            */
+            if(iterations % 8192 == 0)
+               {
+               auto time_taken = std::chrono::high_resolution_clock::now() - start;
+               auto usec_taken = std::chrono::duration_cast<std::chrono::microseconds>(time_taken);
+               if(usec_taken > usec_per_block)
+                  break;
+               }
+            }
+         }
+      else
          {
-         mac->update(U);
-         mac->final(&U[0]);
-         xor_buf(T, &U[0], T_size);
+         for(size_t i = 1; i != iterations; ++i)
+            {
+            mac->update(U);
+            mac->final(&U[0]);
+            xor_buf(T, &U[0], T_size);
+            }
          }
 
       key_len -= T_size;
@@ -62,7 +105,7 @@ OctetString PKCS5_PBKDF2::derive_key(size_t key_len,
       ++counter;
       }
 
-   return key;
+   return std::make_pair(iterations, key);
    }
 
 }