For CBC, ECB, and XTS the output length of a zero length input is well

defined, so don't fail. Fix XTS, as XTS always uses ciphertext
stealing the value of output_length had been incorrect in rounding up
to the block size.

3 files changed, 9 insertions, 7 deletions

diff --git a/src/lib/modes/cbc/cbc.cpp b/src/lib/modes/cbc/cbc.cpp
index dd6550fce..85241cf53 100644
--- a/src/lib/modes/cbc/cbc.cpp
+++ b/src/lib/modes/cbc/cbc.cpp
@@ -105,8 +105,10 @@ size_t CBC_Encryption::minimum_final_size() const
 
 size_t CBC_Encryption::output_length(size_t input_length) const
    {
-   BOTAN_ASSERT(input_length != 0, "CBC_Encryption::output_length() call");
-   return round_up(input_length, cipher().block_size());
+   if(input_length == 0)
+      return cipher().block_size();
+   else
+      return round_up(input_length, cipher().block_size());
    }
 
 void CBC_Encryption::update(secure_vector<byte>& buffer, size_t offset)
diff --git a/src/lib/modes/ecb/ecb.cpp b/src/lib/modes/ecb/ecb.cpp
index 6de00f18a..e5794d8e1 100644
--- a/src/lib/modes/ecb/ecb.cpp
+++ b/src/lib/modes/ecb/ecb.cpp
@@ -83,8 +83,10 @@ size_t ECB_Encryption::minimum_final_size() const
 
 size_t ECB_Encryption::output_length(size_t input_length) const
    {
-   BOTAN_ASSERT(input_length != 0, "ECB_Encryption::output_length() call");
-   return round_up(input_length, cipher().block_size());
+   if(input_length == 0)
+      return cipher().block_size();
+   else
+      return round_up(input_length, cipher().block_size());
    }
 
 void ECB_Encryption::update(secure_vector<byte>& buffer, size_t offset)
diff --git a/src/lib/modes/xts/xts.cpp b/src/lib/modes/xts/xts.cpp
index 4eaf03fe5..046de216f 100644
--- a/src/lib/modes/xts/xts.cpp
+++ b/src/lib/modes/xts/xts.cpp
@@ -135,8 +135,7 @@ void XTS_Mode::update_tweak(size_t which)
 
 size_t XTS_Encryption::output_length(size_t input_length) const
    {
-   BOTAN_ASSERT(input_length != 0, "XTS_Encryption::output_length() call");
-   return round_up(input_length, cipher().block_size());
+   return input_length;
    }
 
 void XTS_Encryption::update(secure_vector<byte>& buffer, size_t offset)
@@ -214,7 +213,6 @@ void XTS_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
 
 size_t XTS_Decryption::output_length(size_t input_length) const
    {
-   // might be less
    return input_length;
    }