diff --git a/implementations/encrypted/Cipher.cpp b/implementations/encrypted/Cipher.cpp
new file mode 100644
index 00000000..c866c29b
--- /dev/null
+++ b/implementations/encrypted/Cipher.cpp
@@ -0,0 +1,2 @@
+#include "Cipher.h"
+
diff --git a/implementations/encrypted/Cipher.h b/implementations/encrypted/Cipher.h
new file mode 100644
index 00000000..b5528a34
--- /dev/null
+++ b/implementations/encrypted/Cipher.h
@@ -0,0 +1,26 @@
+#pragma once
+#ifndef MESSMER_BLOCKSTORE_IMPLEMENTATIONS_ENCRYPTED_CIPHER_H_
+#define MESSMER_BLOCKSTORE_IMPLEMENTATIONS_ENCRYPTED_CIPHER_H_
+
+#include <cryptopp/cryptopp/modes.h>
+
+namespace blockstore {
+namespace encrypted {
+
+class Cipher {
+public:
+  virtual ~Cipher() {}
+
+  virtual unsigned int ciphertextBlockSize(unsigned int ciphertextBlockSize) const = 0;
+  virtual unsigned int plaintextBlockSize(unsigned int plaintextBlockSize) const = 0;
+
+  virtual void encrypt(const byte *plaintext, unsigned int plaintextSize, byte *ciphertext) const = 0;
+  virtual void decrypt(const byte *ciphertext, byte *plaintext, unsigned int plaintextSize) const = 0;
+};
+
+}
+}
+
+
+
+#endif
diff --git a/implementations/encrypted/EncryptedBlock.cpp b/implementations/encrypted/EncryptedBlock.cpp
index 59da307d..5f66d9c9 100644
--- a/implementations/encrypted/EncryptedBlock.cpp
+++ b/implementations/encrypted/EncryptedBlock.cpp
@@ -1,91 +1 @@
 #include "EncryptedBlock.h"
-#include <cryptopp/cryptopp/modes.h>
-
-#include "../../utils/BlockStoreUtils.h"
-
-using CryptoPP::CFB_Mode;
-using CryptoPP::AES;
-
-using std::make_unique;
-
-//TODO not only encryption, but also hmac
-
-namespace blockstore {
-namespace encrypted {
-
-constexpr unsigned int EncryptedBlock::IV_SIZE;
-
-std::unique_ptr<EncryptedBlock> EncryptedBlock::TryCreateNew(BlockStore *baseBlockStore, const Key &key, Data data, const EncryptionKey &encKey) {
-  Data encrypted = _encrypt(data, encKey);
-  auto baseBlock = baseBlockStore->tryCreate(key, std::move(encrypted));
-  if (baseBlock.get() == nullptr) {
-	//TODO Test this code branch
-	return nullptr;
-  }
-
-  return make_unique<EncryptedBlock>(std::move(baseBlock), encKey, std::move(data));
-}
-
-EncryptedBlock::EncryptedBlock(std::unique_ptr<Block> baseBlock, const EncryptionKey &encKey)
-    :EncryptedBlock(std::move(baseBlock), encKey, Data(USEABLE_BLOCK_SIZE(baseBlock->size()))) {
-  _decryptFromBaseBlock();
-}
-
-EncryptedBlock::EncryptedBlock(std::unique_ptr<Block> baseBlock, const EncryptionKey &encKey, Data plaintextData)
-    :Block(baseBlock->key()),
-	 _baseBlock(std::move(baseBlock)),
-	 _plaintextData(std::move(plaintextData)),
-	 _encKey(encKey),
-	 _dataChanged(false) {
-}
-
-EncryptedBlock::~EncryptedBlock() {
-  _encryptToBaseBlock();
-}
-
-const void *EncryptedBlock::data() const {
-  return _plaintextData.data();
-}
-
-void EncryptedBlock::write(const void *source, uint64_t offset, uint64_t size) {
-  assert(offset <= _plaintextData.size() && offset + size <= _plaintextData.size()); //Also check offset < _data->size() because of possible overflow in the addition
-  std::memcpy((uint8_t*)_plaintextData.data()+offset, source, size);
-  _dataChanged = true;
-}
-
-void EncryptedBlock::flush() {
-  _encryptToBaseBlock();
-  return _baseBlock->flush();
-}
-
-size_t EncryptedBlock::size() const {
-  return _plaintextData.size();
-}
-
-void EncryptedBlock::_decryptFromBaseBlock() {
-  const byte *iv = (byte*)_baseBlock->data();
-  const byte *data = (byte*)_baseBlock->data() + IV_SIZE;
-  auto decryption = CFB_Mode<AES>::Decryption((byte*)_encKey.data(), EncryptionKey::BINARY_LENGTH, iv);
-  decryption.ProcessData((byte*)_plaintextData.data(), data, _plaintextData.size());
-}
-
-void EncryptedBlock::_encryptToBaseBlock() {
-  if (_dataChanged) {
-	Data encrypted = _encrypt(_plaintextData, _encKey);
-    _baseBlock->write(encrypted.data(), 0, encrypted.size());
-    _dataChanged = false;
-  }
-}
-
-Data EncryptedBlock::_encrypt(const Data &plaintext, const EncryptionKey &encKey) {
-  FixedSizeData<IV_SIZE> iv = FixedSizeData<IV_SIZE>::CreateRandom();
-  auto encryption = CFB_Mode<AES>::Encryption(encKey.data(), EncryptionKey::BINARY_LENGTH, iv.data());
-  //TODO More performance when not using "Data encrypted" object, but encrypting directly to a target that was specified via a parameter using a specialized CryptoPP sink
-  Data encrypted(IV_SIZE + plaintext.size());
-  std::memcpy(encrypted.data(), iv.data(), IV_SIZE);
-  encryption.ProcessData((byte*)encrypted.data() + IV_SIZE, (byte*)plaintext.data(), plaintext.size());
-  return encrypted;
-}
-
-}
-}
diff --git a/implementations/encrypted/EncryptedBlock.h b/implementations/encrypted/EncryptedBlock.h
index 84b66019..4be10ef9 100644
--- a/implementations/encrypted/EncryptedBlock.h
+++ b/implementations/encrypted/EncryptedBlock.h
@@ -3,7 +3,7 @@
 #define BLOCKSTORE_IMPLEMENTATIONS_ENCRYPTED_ENCRYPTEDBLOCK_H_
 
 #include "../../interface/Block.h"
-#include "EncryptionKey.h"
+#include "Cipher.h"
 #include "../../utils/Data.h"
 #include "../../interface/BlockStore.h"
 
@@ -12,16 +12,19 @@
 
 namespace blockstore {
 namespace encrypted {
-class EncryptedBlockStore;
+template<class Cipher> class EncryptedBlockStore;
 
+//TODO not only encryption, but also hmac
+
+template<class Cipher>
 class EncryptedBlock: public Block {
 public:
-  //TODO Storing key twice (in parent class and in object pointed to). Once would be enough.
-  EncryptedBlock(std::unique_ptr<Block> baseBlock, const EncryptionKey &encKey);
-  EncryptedBlock(std::unique_ptr<Block> baseBlock, const EncryptionKey &encKey, Data plaintextData);
-  virtual ~EncryptedBlock();
+  static std::unique_ptr<EncryptedBlock> TryCreateNew(BlockStore *baseBlockStore, const Key &key, Data data, const typename Cipher::EncryptionKey &encKey);
 
-  static std::unique_ptr<EncryptedBlock> TryCreateNew(BlockStore *baseBlockStore, const Key &key, Data data, const EncryptionKey &encKey);
+  //TODO Storing key twice (in parent class and in object pointed to). Once would be enough.
+  EncryptedBlock(std::unique_ptr<Block> baseBlock, const typename Cipher::EncryptionKey &key);
+  EncryptedBlock(std::unique_ptr<Block> baseBlock, const typename Cipher::EncryptionKey &key, Data plaintextData);
+  virtual ~EncryptedBlock();
 
   const void *data() const override;
   void write(const void *source, uint64_t offset, uint64_t size) override;
@@ -29,33 +32,99 @@ public:
 
   size_t size() const override;
 
-  static constexpr unsigned int BASE_BLOCK_SIZE(unsigned int useableBlockSize) {
-    return useableBlockSize + IV_SIZE;
-  }
-
-  static constexpr unsigned int USEABLE_BLOCK_SIZE(unsigned int baseBlockSize) {
-    return baseBlockSize - IV_SIZE;
-  }
+  std::unique_ptr<Block> releaseBlock();
 
 private:
   std::unique_ptr<Block> _baseBlock;
   Data _plaintextData;
-  EncryptionKey _encKey;
+  typename Cipher::EncryptionKey _encKey;
   bool _dataChanged;
 
-  static constexpr unsigned int IV_SIZE = CryptoPP::AES::BLOCKSIZE;
-
-  byte *baseBlockIV();
-  byte *baseBlockData();
-
   void _encryptToBaseBlock();
   void _decryptFromBaseBlock();
 
-  static Data _encrypt(const Data &plaintext, const EncryptionKey &encKey);
-
   DISALLOW_COPY_AND_ASSIGN(EncryptedBlock);
 };
 
+
+
+template<class Cipher>
+std::unique_ptr<EncryptedBlock<Cipher>> EncryptedBlock<Cipher>::TryCreateNew(BlockStore *baseBlockStore, const Key &key, Data data, const typename Cipher::EncryptionKey &encKey) {
+  Data encrypted(Cipher::ciphertextSize(data.size()));
+  Cipher::encrypt((byte*)data.data(), data.size(), (byte*)encrypted.data(), encKey);
+  auto baseBlock = baseBlockStore->tryCreate(key, std::move(encrypted));
+  if (baseBlock.get() == nullptr) {
+    //TODO Test this code branch
+    return nullptr;
+  }
+
+  return std::make_unique<EncryptedBlock>(std::move(baseBlock), encKey, std::move(data));
+}
+
+template<class Cipher>
+EncryptedBlock<Cipher>::EncryptedBlock(std::unique_ptr<Block> baseBlock, const typename Cipher::EncryptionKey &encKey)
+    :EncryptedBlock(std::move(baseBlock), encKey, Data(Cipher::plaintextSize(baseBlock->size()))) {
+  _decryptFromBaseBlock();
+}
+
+template<class Cipher>
+EncryptedBlock<Cipher>::EncryptedBlock(std::unique_ptr<Block> baseBlock, const typename Cipher::EncryptionKey &encKey, Data plaintextData)
+    :Block(baseBlock->key()),
+   _baseBlock(std::move(baseBlock)),
+   _plaintextData(std::move(plaintextData)),
+   _encKey(encKey),
+   _dataChanged(false) {
+}
+
+template<class Cipher>
+EncryptedBlock<Cipher>::~EncryptedBlock() {
+  _encryptToBaseBlock();
+}
+
+template<class Cipher>
+const void *EncryptedBlock<Cipher>::data() const {
+  return _plaintextData.data();
+}
+
+template<class Cipher>
+void EncryptedBlock<Cipher>::write(const void *source, uint64_t offset, uint64_t size) {
+  assert(offset <= _plaintextData.size() && offset + size <= _plaintextData.size()); //Also check offset < _data->size() because of possible overflow in the addition
+  std::memcpy((uint8_t*)_plaintextData.data()+offset, source, size);
+  _dataChanged = true;
+}
+
+template<class Cipher>
+void EncryptedBlock<Cipher>::flush() {
+  _encryptToBaseBlock();
+  return _baseBlock->flush();
+}
+
+template<class Cipher>
+size_t EncryptedBlock<Cipher>::size() const {
+  return _plaintextData.size();
+}
+
+template<class Cipher>
+void EncryptedBlock<Cipher>::_decryptFromBaseBlock() {
+  //TODO Change BlockStore so we can read their "class Data" objects instead of "void *data()", and then we can change the Cipher interface to take Data objects instead of "byte *" + size
+  Cipher::decrypt((byte*)_baseBlock->data(), (byte*)_plaintextData.data(), _plaintextData.size(), _encKey);
+}
+
+template<class Cipher>
+void EncryptedBlock<Cipher>::_encryptToBaseBlock() {
+  if (_dataChanged) {
+    Data encrypted(Cipher::ciphertextSize(_plaintextData.size()));
+    Cipher::encrypt((byte*)_plaintextData.data(), _plaintextData.size(), (byte*)encrypted.data(), _encKey);
+    _baseBlock->write(encrypted.data(), 0, encrypted.size());
+    _dataChanged = false;
+  }
+}
+
+template<class Cipher>
+std::unique_ptr<Block> EncryptedBlock<Cipher>::releaseBlock() {
+  return std::move(_baseBlock);
+}
+
 }
 }
 
diff --git a/implementations/encrypted/EncryptedBlockStore.cpp b/implementations/encrypted/EncryptedBlockStore.cpp
index 1eb88f42..5ab7ca32 100644
--- a/implementations/encrypted/EncryptedBlockStore.cpp
+++ b/implementations/encrypted/EncryptedBlockStore.cpp
@@ -1,42 +1 @@
 #include "EncryptedBlockStore.h"
-#include "EncryptedBlock.h"
-#include <messmer/cpp-utils/pointer.h>
-#include "../../utils/BlockStoreUtils.h"
-
-using std::unique_ptr;
-using std::make_unique;
-
-namespace blockstore {
-namespace encrypted {
-
-EncryptedBlockStore::EncryptedBlockStore(unique_ptr<BlockStore> baseBlockStore, const EncryptionKey &encKey)
- : _baseBlockStore(std::move(baseBlockStore)), _encKey(encKey) {
-}
-
-Key EncryptedBlockStore::createKey() {
-  return _baseBlockStore->createKey();
-}
-
-unique_ptr<Block> EncryptedBlockStore::tryCreate(const Key &key, Data data) {
-  return EncryptedBlock::TryCreateNew(_baseBlockStore.get(), key, std::move(data), _encKey);
-}
-
-unique_ptr<Block> EncryptedBlockStore::load(const Key &key) {
-  auto block = _baseBlockStore->load(key);
-  if (block.get() == nullptr) {
-    return nullptr;
-  }
-  return make_unique<EncryptedBlock>(std::move(block), _encKey);
-}
-
-void EncryptedBlockStore::remove(unique_ptr<Block> block) {
-  return _baseBlockStore->remove(std::move(block));
-}
-
-uint64_t EncryptedBlockStore::numBlocks() const {
-  return _baseBlockStore->numBlocks();
-}
-
-}
-}
-
diff --git a/implementations/encrypted/EncryptedBlockStore.h b/implementations/encrypted/EncryptedBlockStore.h
index 2e897d1d..c7933216 100644
--- a/implementations/encrypted/EncryptedBlockStore.h
+++ b/implementations/encrypted/EncryptedBlockStore.h
@@ -4,14 +4,17 @@
 
 #include "../../interface/BlockStore.h"
 #include <messmer/cpp-utils/macros.h>
-#include "EncryptionKey.h"
+#include <messmer/cpp-utils/pointer.h>
+#include "Cipher.h"
+#include "EncryptedBlock.h"
 
 namespace blockstore {
 namespace encrypted {
 
+template<class Cipher>
 class EncryptedBlockStore: public BlockStore {
 public:
-  EncryptedBlockStore(std::unique_ptr<BlockStore> baseBlockStore, const EncryptionKey &encKey);
+  EncryptedBlockStore(std::unique_ptr<BlockStore> baseBlockStore, const typename Cipher::EncryptionKey &encKey);
 
   Key createKey() override;
   std::unique_ptr<Block> tryCreate(const Key &key, Data data) override;
@@ -21,11 +24,48 @@ public:
 
 private:
   std::unique_ptr<BlockStore> _baseBlockStore;
-  EncryptionKey _encKey;
+  typename Cipher::EncryptionKey _encKey;
 
   DISALLOW_COPY_AND_ASSIGN(EncryptedBlockStore);
 };
 
+
+
+template<class Cipher>
+EncryptedBlockStore<Cipher>::EncryptedBlockStore(std::unique_ptr<BlockStore> baseBlockStore, const typename Cipher::EncryptionKey &encKey)
+ : _baseBlockStore(std::move(baseBlockStore)), _encKey(encKey) {
+}
+
+template<class Cipher>
+Key EncryptedBlockStore<Cipher>::createKey() {
+  return _baseBlockStore->createKey();
+}
+
+template<class Cipher>
+std::unique_ptr<Block> EncryptedBlockStore<Cipher>::tryCreate(const Key &key, Data data) {
+  return EncryptedBlock<Cipher>::TryCreateNew(_baseBlockStore.get(), key, std::move(data), _encKey);
+}
+
+template<class Cipher>
+std::unique_ptr<Block> EncryptedBlockStore<Cipher>::load(const Key &key) {
+  auto block = _baseBlockStore->load(key);
+  if (block.get() == nullptr) {
+    return nullptr;
+  }
+  return std::make_unique<EncryptedBlock<Cipher>>(std::move(block), _encKey);
+}
+
+template<class Cipher>
+void EncryptedBlockStore<Cipher>::remove(std::unique_ptr<Block> block) {
+  auto baseBlock = cpputils::dynamic_pointer_move<EncryptedBlock<Cipher>>(block)->releaseBlock();
+  return _baseBlockStore->remove(std::move(baseBlock));
+}
+
+template<class Cipher>
+uint64_t EncryptedBlockStore<Cipher>::numBlocks() const {
+  return _baseBlockStore->numBlocks();
+}
+
 }
 }
 
diff --git a/implementations/encrypted/EncryptionKey.cpp b/implementations/encrypted/EncryptionKey.cpp
deleted file mode 100644
index 18a97b45..00000000
--- a/implementations/encrypted/EncryptionKey.cpp
+++ /dev/null
@@ -1 +0,0 @@
-#include "EncryptionKey.h"
diff --git a/implementations/encrypted/EncryptionKey.h b/implementations/encrypted/EncryptionKey.h
deleted file mode 100644
index 97cd7a9f..00000000
--- a/implementations/encrypted/EncryptionKey.h
+++ /dev/null
@@ -1,15 +0,0 @@
-#pragma once
-#ifndef MESSMER_BLOCKSTORE_IMPLEMENTATIONS_ENCRYPTED_ENCRYPTIONKEY_H_
-#define MESSMER_BLOCKSTORE_IMPLEMENTATIONS_ENCRYPTED_ENCRYPTIONKEY_H_
-
-#include "../../utils/FixedSizeData.h"
-
-namespace blockstore {
-namespace encrypted {
-
-using EncryptionKey = FixedSizeData<CryptoPP::AES::MAX_KEYLENGTH>;
-
-}
-}
-
-#endif
diff --git a/implementations/encrypted/ciphers/AES256_CFB.cpp b/implementations/encrypted/ciphers/AES256_CFB.cpp
new file mode 100644
index 00000000..bad5562f
--- /dev/null
+++ b/implementations/encrypted/ciphers/AES256_CFB.cpp
@@ -0,0 +1,27 @@
+#include <cryptopp/cryptopp/modes.h>
+#include "AES256_CFB.h"
+
+using CryptoPP::CFB_Mode;
+using CryptoPP::AES;
+
+namespace blockstore {
+namespace encrypted {
+
+constexpr unsigned int AES256_CFB::IV_SIZE;
+
+void AES256_CFB::encrypt(const byte *plaintext, unsigned int plaintextSize, byte *ciphertext, const EncryptionKey &encKey) {
+  FixedSizeData<IV_SIZE> iv = FixedSizeData<IV_SIZE>::CreateRandom();
+  auto encryption = CFB_Mode<AES>::Encryption(encKey.data(), encKey.BINARY_LENGTH, iv.data());
+  std::memcpy(ciphertext, iv.data(), IV_SIZE);
+  encryption.ProcessData(ciphertext + IV_SIZE, plaintext, plaintextSize);
+}
+
+void AES256_CFB::decrypt(const byte *ciphertext, byte *plaintext, unsigned int plaintextSize, const EncryptionKey &encKey) {
+  const byte *iv = ciphertext;
+  const byte *data = ciphertext + IV_SIZE;
+  auto decryption = CFB_Mode<AES>::Decryption((byte*)encKey.data(), encKey.BINARY_LENGTH, iv);
+  decryption.ProcessData(plaintext, data, plaintextSize);
+}
+
+}
+}
diff --git a/implementations/encrypted/ciphers/AES256_CFB.h b/implementations/encrypted/ciphers/AES256_CFB.h
new file mode 100644
index 00000000..16c8e5f8
--- /dev/null
+++ b/implementations/encrypted/ciphers/AES256_CFB.h
@@ -0,0 +1,36 @@
+#pragma once
+#ifndef MESSMER_BLOCKSTORE_IMPLEMENTATIONS_ENCRYPTED_CIPHERS_AES256_CFB_H_
+#define MESSMER_BLOCKSTORE_IMPLEMENTATIONS_ENCRYPTED_CIPHERS_AES256_CFB_H_
+
+#include "../../../utils/FixedSizeData.h"
+#include <cryptopp/cryptopp/aes.h>
+
+namespace blockstore {
+namespace encrypted {
+
+class AES256_CFB {
+public:
+  using EncryptionKey = FixedSizeData<32>;
+  static_assert(32 == CryptoPP::AES::MAX_KEYLENGTH, "If AES offered larger keys, we should offer a variant with it");
+
+  AES256_CFB(const EncryptionKey &key);
+
+  static constexpr unsigned int ciphertextSize(unsigned int plaintextBlockSize) {
+    return plaintextBlockSize + IV_SIZE;
+  }
+
+  static constexpr unsigned int plaintextSize(unsigned int ciphertextBlockSize) {
+    return ciphertextBlockSize - IV_SIZE;
+  }
+
+  static void encrypt(const byte *plaintext, unsigned int plaintextSize, byte *ciphertext, const EncryptionKey &key);
+  static void decrypt(const byte *ciphertext, byte *plaintext, unsigned int plaintextSize, const EncryptionKey &key);
+
+private:
+  static constexpr unsigned int IV_SIZE = CryptoPP::AES::BLOCKSIZE;
+};
+
+}
+}
+
+#endif
diff --git a/test/implementations/encrypted/EncryptedBlockStoreTest.cpp b/test/implementations/encrypted/EncryptedBlockStoreTest.cpp
index b5c6eb29..4a8b35bb 100644
--- a/test/implementations/encrypted/EncryptedBlockStoreTest.cpp
+++ b/test/implementations/encrypted/EncryptedBlockStoreTest.cpp
@@ -1,3 +1,4 @@
+#include "../../../implementations/encrypted/ciphers/AES256_CFB.h"
 #include "../../../implementations/encrypted/EncryptedBlockStore.h"
 #include "../../../implementations/testfake/FakeBlockStore.h"
 #include "../../testutils/BlockStoreTest.h"
@@ -6,8 +7,8 @@
 
 using blockstore::BlockStore;
 using blockstore::encrypted::EncryptedBlockStore;
-using blockstore::encrypted::EncryptionKey;
 using blockstore::testfake::FakeBlockStore;
+using blockstore::encrypted::AES256_CFB;
 
 using std::unique_ptr;
 using std::make_unique;
@@ -15,7 +16,7 @@ using std::make_unique;
 class EncryptedBlockStoreTestFixture: public BlockStoreTestFixture {
 public:
   unique_ptr<BlockStore> createBlockStore() override {
-    return make_unique<EncryptedBlockStore>(make_unique<FakeBlockStore>(), EncryptionKey::FromString("1491BB4932A389EE14BC7090A272EE5517627CFA147A971A8E6E747E0C772972"));
+    return make_unique<EncryptedBlockStore<AES256_CFB>>(make_unique<FakeBlockStore>(), AES256_CFB::EncryptionKey::FromString("1491BB4932A389EE14BC7090A272EE5517627CFA147A971A8E6E747E0C772972"));
   }
 };
 
diff --git a/utils/FixedSizeData.h b/utils/FixedSizeData.h
index f7b70f5c..1199275f 100644
--- a/utils/FixedSizeData.h
+++ b/utils/FixedSizeData.h
@@ -9,7 +9,7 @@
 
 namespace blockstore {
 
-template<int SIZE>
+template<unsigned int SIZE>
 class FixedSizeData {
 public:
   //Non-virtual destructor because we want objects to be small
@@ -35,28 +35,28 @@ private:
   unsigned char _data[BINARY_LENGTH];
 };
 
-template<int SIZE> bool operator==(const FixedSizeData<SIZE> &lhs, const FixedSizeData<SIZE> &rhs);
-template<int SIZE> bool operator!=(const FixedSizeData<SIZE> &lhs, const FixedSizeData<SIZE> &rhs);
+template<unsigned int SIZE> bool operator==(const FixedSizeData<SIZE> &lhs, const FixedSizeData<SIZE> &rhs);
+template<unsigned int SIZE> bool operator!=(const FixedSizeData<SIZE> &lhs, const FixedSizeData<SIZE> &rhs);
 
 // ----- Implementation -----
 
-template<int SIZE> constexpr unsigned int FixedSizeData<SIZE>::BINARY_LENGTH;
-template<int SIZE> constexpr unsigned int FixedSizeData<SIZE>::STRING_LENGTH;
+template<unsigned int SIZE> constexpr unsigned int FixedSizeData<SIZE>::BINARY_LENGTH;
+template<unsigned int SIZE> constexpr unsigned int FixedSizeData<SIZE>::STRING_LENGTH;
 
-template<int SIZE>
+template<unsigned int SIZE>
 CryptoPP::AutoSeededRandomPool &FixedSizeData<SIZE>::RandomPool() {
   static CryptoPP::AutoSeededRandomPool singleton;
   return singleton;
 }
 
-template<int SIZE>
+template<unsigned int SIZE>
 FixedSizeData<SIZE> FixedSizeData<SIZE>::CreateRandom() {
   FixedSizeData<SIZE> result;
   RandomPool().GenerateBlock(result._data, BINARY_LENGTH);
   return result;
 }
 
-template<int SIZE>
+template<unsigned int SIZE>
 FixedSizeData<SIZE> FixedSizeData<SIZE>::FromString(const std::string &data) {
   assert(data.size() == STRING_LENGTH);
   FixedSizeData<SIZE> result;
@@ -68,7 +68,7 @@ FixedSizeData<SIZE> FixedSizeData<SIZE>::FromString(const std::string &data) {
   return result;
 }
 
-template<int SIZE>
+template<unsigned int SIZE>
 std::string FixedSizeData<SIZE>::ToString() const {
   std::string result;
   CryptoPP::ArraySource(_data, BINARY_LENGTH, true,
@@ -80,29 +80,29 @@ std::string FixedSizeData<SIZE>::ToString() const {
   return result;
 }
 
-template<int SIZE>
+template<unsigned int SIZE>
 const unsigned char *FixedSizeData<SIZE>::data() const {
   return _data;
 }
 
-template<int SIZE>
+template<unsigned int SIZE>
 void FixedSizeData<SIZE>::ToBinary(void *target) const {
   std::memcpy(target, _data, BINARY_LENGTH);
 }
 
-template<int SIZE>
+template<unsigned int SIZE>
 FixedSizeData<SIZE> FixedSizeData<SIZE>::FromBinary(const void *source) {
   FixedSizeData<SIZE> result;
   std::memcpy(result._data, source, BINARY_LENGTH);
   return result;
 }
 
-template<int SIZE>
+template<unsigned int SIZE>
 bool operator==(const FixedSizeData<SIZE> &lhs, const FixedSizeData<SIZE> &rhs) {
   return 0 == std::memcmp(lhs.data(), rhs.data(), FixedSizeData<SIZE>::BINARY_LENGTH);
 }
 
-template<int SIZE>
+template<unsigned int SIZE>
 bool operator!=(const FixedSizeData<SIZE> &lhs, const FixedSizeData<SIZE> &rhs) {
   return !operator==(lhs, rhs);
 }