TLS improvements

Use constant time operations when checking CBC padding in TLS decryption

Fix a bug in decoding ClientHellos that prevented DTLS rehandshakes
from working: on decode the session id and hello cookie would be
swapped, causing confusion between client and server.

Various changes in the service of finding the above DTLS bug that
should have been done before now anyway - better control of handshake
timeouts (via TLS::Policy), better reporting of handshake state in the
case of an error, and finally expose the facility for per-message
application callbacks.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/lib/rng/rng.h b/src/lib/rng/rng.h
index 6ee67f66f..261880d5d 100644
--- a/src/lib/rng/rng.h
+++ b/src/lib/rng/rng.h
@@ -75,6 +75,14 @@ class BOTAN_DLL RandomNumberGenerator
       */
       byte next_byte() { return get_random<byte>(); }
 
+      byte next_nonzero_byte()
+         {
+         byte b = next_byte();
+         while(b == 0)
+            b = next_byte();
+         return b;
+         }
+
       /**
       * Check whether this RNG is seeded.
       * @return true if this RNG was already seeded, false otherwise.