Fix an EAX bug in reset()

It failed to reset any data that had been fed into CMAC so far,
so a sequence with

eax->set_key(key);
eax->start(nonce);
eax->process(discarded_bits);
eax->reset();
eax->start(second_nonce);
eax->process(second_msg);

would produce incorrect results

2 files changed, 12 insertions, 7 deletions

diff --git a/src/lib/modes/aead/eax/eax.cpp b/src/lib/modes/aead/eax/eax.cpp
index dbd916db9..a03c5e802 100644
--- a/src/lib/modes/aead/eax/eax.cpp
+++ b/src/lib/modes/aead/eax/eax.cpp
@@ -57,6 +57,12 @@ void EAX_Mode::reset()
    {
    m_ad_mac.clear();
    m_nonce_mac.clear();
+
+   // Clear out any data added to the CMAC calculation
+   try {
+      m_cmac->final();
+   }
+   catch(Key_Not_Set&) {}
    }
 
 std::string EAX_Mode::name() const
@@ -115,6 +121,7 @@ void EAX_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)
 
 size_t EAX_Encryption::process(uint8_t buf[], size_t sz)
    {
+   BOTAN_ASSERT_NOMSG(m_nonce_mac.empty() == false);
    m_ctr->cipher(buf, buf, sz);
    m_cmac->update(buf, sz);
    return sz;
@@ -122,6 +129,7 @@ size_t EAX_Encryption::process(uint8_t buf[], size_t sz)
 
 void EAX_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
    {
+   BOTAN_ASSERT_NOMSG(m_nonce_mac.empty() == false);
    update(buffer, offset);
 
    secure_vector<uint8_t> data_mac = m_cmac->final();
diff --git a/src/tests/test_aead.cpp b/src/tests/test_aead.cpp
index ce9c3e095..992278c0f 100644
--- a/src/tests/test_aead.cpp
+++ b/src/tests/test_aead.cpp
@@ -1,5 +1,5 @@
 /*
-* (C) 2014,2015,2016 Jack Lloyd
+* (C) 2014,2015,2016,2018 Jack Lloyd
 * (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
@@ -44,9 +44,8 @@ class AEAD_Tests final : public Text_Based_Test
                                [&]() { enc->set_associated_data(ad.data(), ad.size()); });
             }
 
-         // First some tests for reset() to make sure it resets what we need it to
-         // set garbage values
-         enc->set_key(mutate_vec(key));
+         // Ensure that test resets AD and message state
+         enc->set_key(key);
          enc->set_ad(mutate_vec(ad));
          enc->start(mutate_vec(nonce));
 
@@ -57,7 +56,6 @@ class AEAD_Tests final : public Text_Based_Test
          enc->reset();
 
          // now try to encrypt with correct values
-         enc->set_key(key);
          enc->set_ad(ad);
          enc->start(nonce);
 
@@ -178,7 +176,7 @@ class AEAD_Tests final : public Text_Based_Test
 
          // First some tests for reset() to make sure it resets what we need it to
          // set garbage values
-         dec->set_key(mutate_vec(key));
+         dec->set_key(key);
          dec->set_ad(mutate_vec(ad));
          dec->start(mutate_vec(nonce));
 
@@ -192,7 +190,6 @@ class AEAD_Tests final : public Text_Based_Test
          try
             {
             // now try to decrypt with correct values
-            dec->set_key(key);
             dec->set_ad(ad);
             dec->start(nonce);