Add AEAD_Mode::output_length

1 files changed, 9 insertions, 0 deletions

diff --git a/src/aead/gcm/gcm.h b/src/aead/gcm/gcm.h
index bc7eaae20..f36aafc5f 100644
--- a/src/aead/gcm/gcm.h
+++ b/src/aead/gcm/gcm.h
@@ -68,6 +68,9 @@ class BOTAN_DLL GCM_Encryption : public GCM_Mode
       GCM_Encryption(BlockCipher* cipher, size_t tag_size = 16) :
          GCM_Mode(cipher, tag_size) {}
 
+      size_t output_length(size_t input_length) const override
+         { return input_length + tag_size(); }
+
       size_t minimum_final_size() const override { return 0; }
 
       void update(secure_vector<byte>& blocks, size_t offset) override;
@@ -88,6 +91,12 @@ class BOTAN_DLL GCM_Decryption : public GCM_Mode
       GCM_Decryption(BlockCipher* cipher, size_t tag_size = 16) :
          GCM_Mode(cipher, tag_size) {}
 
+      size_t output_length(size_t input_length) const override
+         {
+         BOTAN_ASSERT(input_length > tag_size(), "Sufficient input");
+         return input_length - tag_size();
+         }
+
       size_t minimum_final_size() const override { return tag_size(); }
 
       void update(secure_vector<byte>& blocks, size_t offset) override;