Implement AES-CTR for NSS.

crypto/encryptor.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CRYPTO_ENCRYPTOR_H_
 #define CRYPTO_ENCRYPTOR_H_
 #pragma once
 
 #include <string>
 
+#include "base/basictypes.h"
+#include "base/scoped_ptr.h"
 #include "build/build_config.h"
-
 #if defined(USE_NSS)
 #include "crypto/scoped_nss_types.h"
 #elif defined(OS_WIN)
 #include "crypto/scoped_capi_types.h"
 #endif
 
 namespace crypto {
 
 class SymmetricKey;
 
 class Encryptor {
  public:
   enum Mode {
-    CBC
+    CBC,
+    CTR,
   };
+
+  class Counter {

[wtc, 2011/06/14 18:11:06]

Please document this class.  At least mention it is related
to the CTR mode.

Your Counter class is less general than the one used in
PKCS #11.  Why?

[Alpha Left Google, 2011/06/14 22:22:43]

This is implemented to support AES-CTR-128 mode only. This is the only CTR mode
that we use. Since the Encryptor interface assumes 128-bits already so we don't
need that flexibility in Counter.

+   public:
+    Counter(const std::string& counter);
+    ~Counter();
+
+    // Increment the counter value.
+    void Increment();
+
+    // Write the content of the counter to |buf|. |buf| should have enough
+    // space for |GetLengthInBytes()|.
+    void Write(void* buf);
+
+    // Return the length of this counter.
+    const int GetLengthInBytes() const;

[wtc, 2011/06/14 18:11:06]

GetLengthInBytes() should return size_t.  The return value
should not be const:
    size_t GetLengthInBytes() const;

[Alpha Left Google, 2011/06/14 22:22:43]

Done.

+
+   private:
+    uint64 high_num_;
+    uint64 low_num_;
+  };
+
   Encryptor();
   virtual ~Encryptor();
 
   // Initializes the encryptor using |key| and |iv|. Returns false if either the
   // key or the initialization vector cannot be used.
+  //
+  // When |mode| is CTR then |iv| should be empty.
   bool Init(SymmetricKey* key, Mode mode, const std::string& iv);
 
   // Encrypts |plaintext| into |ciphertext|.
   bool Encrypt(const std::string& plaintext, std::string* ciphertext);
 
   // Decrypts |ciphertext| into |plaintext|.
   bool Decrypt(const std::string& ciphertext, std::string* plaintext);
 
+  // Update the counter value when in CTR mode. Currently only 128-bits
+  // counter value is supported.

[wtc, 2011/06/14 18:11:06]

The limitation of 128-bits counter values should be documented
in the Counter class above instead of here.

[Alpha Left Google, 2011/06/14 22:22:43]

Done.

+  //
+  // Return true only if update was successful.
+  bool UpdateCounter(const std::string& counter);
+
   // TODO(albertb): Support streaming encryption.
 
  private:
+  // Generate a mask using |counter_| to be used for encryption in CTR mode.
+  // Resulting mask will be written to |mask| with |mask_len| bytes.
+  //
+  // The generated mask will always have at least |plaintext_len| bytes and
+  // will be a multiple of the counter length.
+  //
+  // This method is used only in CTR mode.
+  void GenerateCounterMask(size_t plaintext_len,
+                           scoped_array<uint8>* mask,
+                           size_t* mask_len);
+
+  // Mask the |plaintext| message using |mask|. The output will be written to
+  // |ciphertext|. |ciphertext| must have at least |plaintext_len| bytes.
+  void MaskMessage(const void* plaintext,
+                   size_t plaintext_len,
+                   const void* mask,
+                   void* ciphertext) const;
+
   SymmetricKey* key_;
   Mode mode_;
+  scoped_ptr<Counter> counter_;
 
 #if defined(USE_OPENSSL)
   bool Crypt(bool encrypt,  // Pass true to encrypt, false to decrypt.
              const std::string& input,
              std::string* output);
   std::string iv_;
 #elif defined(USE_NSS)
+  bool Crypt(PK11Context* context,
+             const std::string& input,
+             std::string* output);
+  bool CryptCTR(PK11Context* context,
+                const std::string& input,
+                std::string* output);
   ScopedPK11Slot slot_;
   ScopedSECItem param_;
 #elif defined(OS_MACOSX)
   bool Crypt(int /*CCOperation*/ op,
              const std::string& input,
              std::string* output);
 
   std::string iv_;
 #elif defined(OS_WIN)
   ScopedHCRYPTKEY capi_key_;
   DWORD block_size_;
 #endif
 };
 
 }  // namespace crypto
 
 #endif  // CRYPTO_ENCRYPTOR_H_