Add AEAD_Mode::output_length

4 files changed, 34 insertions, 0 deletions

diff --git a/src/aead/aead.h b/src/aead/aead.h
index 1daa67f59..eb9e7ec7d 100644
--- a/src/aead/aead.h
+++ b/src/aead/aead.h
@@ -23,6 +23,13 @@ class AEAD_Mode : public SymmetricAlgorithm
    {
    public:
       /**
+      * Returns the size of the output if this mode is used to process
+      * a message with input_length bytes. Typically this will be
+      * input_length plus or minus the length of the tag.
+      */
+      virtual size_t output_length(size_t input_length) const = 0;
+
+      /**
       * @return size of required blocks to update
       */
       virtual size_t update_granularity() const = 0;
diff --git a/src/aead/eax/eax.h b/src/aead/eax/eax.h
index 6720bdca4..f93e48d22 100644
--- a/src/aead/eax/eax.h
+++ b/src/aead/eax/eax.h
@@ -73,6 +73,9 @@ class BOTAN_DLL EAX_Encryption : public EAX_Mode
       EAX_Encryption(BlockCipher* cipher, size_t tag_size = 16) :
          EAX_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;
@@ -93,6 +96,12 @@ class BOTAN_DLL EAX_Decryption : public EAX_Mode
       EAX_Decryption(BlockCipher* cipher, size_t tag_size = 16) :
          EAX_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;
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;
diff --git a/src/aead/ocb/ocb.h b/src/aead/ocb/ocb.h
index d50710a79..d2b207fd8 100644
--- a/src/aead/ocb/ocb.h
+++ b/src/aead/ocb/ocb.h
@@ -82,6 +82,9 @@ class BOTAN_DLL OCB_Encryption : public OCB_Mode
       OCB_Encryption(BlockCipher* cipher, size_t tag_size = 16) :
          OCB_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;
@@ -101,6 +104,12 @@ class BOTAN_DLL OCB_Decryption : public OCB_Mode
       OCB_Decryption(BlockCipher* cipher, size_t tag_size = 16) :
          OCB_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;