Change how the ANSI X9.31 generator tells that it is seeded. Previously,

it was seeded if and only if the underlying PRNG was seeded. However if
the PRNG always returned as being seeded, we would never generate a V
value, etc (leaving them at the default zero). This would not occur with
any of Botan's built in PRNGs since their implementations require that
add_randomness be called at least once before is_seeded will return true.
However this is not an invariant of the general RandomNumberGenerator
interface.

Now, the X9.31 PRNG is only seeded after it has a) detected that the PRNG
is seeded, and b) generated a new random key and V vector.

1 files changed, 11 insertions, 15 deletions

diff --git a/src/x931_rng.cpp b/src/x931_rng.cpp
index 94d5f9247..99d0730bd 100644
--- a/src/x931_rng.cpp
+++ b/src/x931_rng.cpp
@@ -21,15 +21,15 @@ void ANSI_X931_RNG::randomize(byte out[], u32bit length) throw(PRNG_Unseeded)
 
    while(length)
       {
+      if(position == R.size())
+         update_buffer();
+
       const u32bit copied = std::min(length, R.size() - position);
 
       copy_mem(out, R + position, copied);
       out += copied;
       length -= copied;
       position += copied;
-
-      if(position == R.size())
-         update_buffer();
       }
    }
 
@@ -38,17 +38,15 @@ void ANSI_X931_RNG::randomize(byte out[], u32bit length) throw(PRNG_Unseeded)
 *************************************************/
 void ANSI_X931_RNG::update_buffer()
    {
-   const u32bit BLOCK_SIZE = cipher->BLOCK_SIZE;
-
-   SecureVector<byte> DT(BLOCK_SIZE);
+   SecureVector<byte> DT(cipher->BLOCK_SIZE);
 
    prng->randomize(DT, DT.size());
    cipher->encrypt(DT);
 
-   xor_buf(R, V, DT, BLOCK_SIZE);
+   xor_buf(R, V, DT, cipher->BLOCK_SIZE);
    cipher->encrypt(R);
 
-   xor_buf(V, R, DT, BLOCK_SIZE);
+   xor_buf(V, R, DT, cipher->BLOCK_SIZE);
    cipher->encrypt(V);
 
    position = 0;
@@ -61,12 +59,14 @@ void ANSI_X931_RNG::add_randomness(const byte data[], u32bit length)
    {
    prng->add_entropy(data, length);
 
-   if(is_seeded())
+   if(prng->is_seeded())
       {
       SecureVector<byte> key(cipher->MAXIMUM_KEYLENGTH);
       prng->randomize(key, key.size());
       cipher->set_key(key, key.size());
 
+      if(V.size() != cipher->BLOCK_SIZE)
+         V.create(cipher->BLOCK_SIZE);
       prng->randomize(V, V.size());
 
       update_buffer();
@@ -78,7 +78,7 @@ void ANSI_X931_RNG::add_randomness(const byte data[], u32bit length)
 *************************************************/
 bool ANSI_X931_RNG::is_seeded() const
    {
-   return prng->is_seeded();
+   return V.has_items();
    }
 
 /*************************************************
@@ -114,11 +114,7 @@ ANSI_X931_RNG::ANSI_X931_RNG(const std::string& cipher_name,
    prng = prng_ptr;
    cipher = get_block_cipher(cipher_name);
 
-   const u32bit BLOCK_SIZE = cipher->BLOCK_SIZE;
-
-   V.create(BLOCK_SIZE);
-   R.create(BLOCK_SIZE);
-
+   R.create(cipher->BLOCK_SIZE);
    position = 0;
    }