11 files changed, 59 insertions, 4 deletions
diff --git a/src/lib/stream/chacha/chacha.cpp b/src/lib/stream/chacha/chacha.cpp
index ac81fd70d..40da93029 100644
--- a/src/lib/stream/chacha/chacha.cpp
+++ b/src/lib/stream/chacha/chacha.cpp
@@ -12,8 +12,8 @@ namespace Botan {
 
 ChaCha::ChaCha(size_t rounds) : m_rounds(rounds)
    {
-   if(m_rounds != 12 && m_rounds != 20)
-      throw Invalid_Argument("ChaCha only supports 12 or 20 rounds");
+   if(m_rounds != 8 && m_rounds != 12 && m_rounds != 20)
+      throw Invalid_Argument("ChaCha only supports 8, 12 or 20 rounds");
    }
 
 namespace {
@@ -67,7 +67,6 @@ void chacha(byte output[64], const u32bit input[16], size_t rounds)
    store_le(x14 + input[14], output + 4 * 14);
    store_le(x15 + input[15], output + 4 * 15);
    }
-
 }
 
 /*
@@ -173,4 +172,27 @@ std::string ChaCha::name() const
    return "ChaCha(" + std::to_string(m_rounds) + ")";
    }
 
+void ChaCha::seek(u64bit offset)
+   {
+   if (m_state.size() == 0 && m_buffer.size() == 0)
+      {
+         throw Invalid_State("You have to setup the stream cipher (key and iv)");
+      }
+
+   m_position = offset % m_buffer.size();
+
+   u64bit counter = offset / m_buffer.size();
+
+   byte out[8];
+
+   store_le(counter, out);
+
+   m_state[12] = load_le<u32bit>(out, 0);
+   m_state[13] += load_le<u32bit>(out, 1);
+
+   chacha(m_buffer.data(), m_state.data(), m_rounds);
+
+   ++m_state[12];
+   m_state[13] += (m_state[12] == 0);
+   }
 }
diff --git a/src/lib/stream/chacha/chacha.h b/src/lib/stream/chacha/chacha.h
index ba93d6260..f8f42e41d 100644
--- a/src/lib/stream/chacha/chacha.h
+++ b/src/lib/stream/chacha/chacha.h
@@ -21,7 +21,7 @@ class BOTAN_DLL ChaCha final : public StreamCipher
       StreamCipher* clone() const override { return new ChaCha(m_rounds); }
 
       /**
-      * Currently only 12 or 20 rounds are supported, all others
+      * Currently only 8, 12 or 20 rounds are supported, all others
       * will throw an exception
       */
       ChaCha(size_t rounds);
@@ -42,6 +42,8 @@ class BOTAN_DLL ChaCha final : public StreamCipher
 
       std::string name() const override;
 
+      void seek(u64bit offset) override;
+
    private:
       void key_schedule(const byte key[], size_t key_len) override;
 
diff --git a/src/lib/stream/ctr/ctr.cpp b/src/lib/stream/ctr/ctr.cpp
index f5301c099..43609ba2d 100644
--- a/src/lib/stream/ctr/ctr.cpp
+++ b/src/lib/stream/ctr/ctr.cpp
@@ -125,4 +125,8 @@ void CTR_BE::increment_counter()
    m_pad_pos = 0;
    }
 
+void CTR_BE::seek(u64bit)
+   {
+   throw Not_Implemented("CTR_BE::seek");
+   }
 }
diff --git a/src/lib/stream/ctr/ctr.h b/src/lib/stream/ctr/ctr.h
index 003297b92..5d5556254 100644
--- a/src/lib/stream/ctr/ctr.h
+++ b/src/lib/stream/ctr/ctr.h
@@ -46,6 +46,8 @@ class BOTAN_DLL CTR_BE final : public StreamCipher
       explicit CTR_BE(BlockCipher* cipher);
 
       CTR_BE(BlockCipher* cipher, size_t ctr_size);
+
+      void seek(u64bit offset) override;
    private:
       void key_schedule(const byte key[], size_t key_len) override;
       void increment_counter();
diff --git a/src/lib/stream/ofb/ofb.cpp b/src/lib/stream/ofb/ofb.cpp
index e8cb463db..3337a0c14 100644
--- a/src/lib/stream/ofb/ofb.cpp
+++ b/src/lib/stream/ofb/ofb.cpp
@@ -73,4 +73,9 @@ void OFB::set_iv(const byte iv[], size_t iv_len)
    m_buf_pos = 0;
    }
 
+
+void OFB::seek(u64bit)
+   {
+   throw Exception("OFB does not support seeking");
+   }
 }
diff --git a/src/lib/stream/ofb/ofb.h b/src/lib/stream/ofb/ofb.h
index fecd47d9d..127a06578 100644
--- a/src/lib/stream/ofb/ofb.h
+++ b/src/lib/stream/ofb/ofb.h
@@ -44,6 +44,8 @@ class BOTAN_DLL OFB final : public StreamCipher
       * @param cipher the underlying block cipher to use
       */
       explicit OFB(BlockCipher* cipher);
+
+      void seek(u64bit offset) override;
    private:
       void key_schedule(const byte key[], size_t key_len) override;
 
diff --git a/src/lib/stream/rc4/rc4.cpp b/src/lib/stream/rc4/rc4.cpp
index 895f38091..a4dea9e2b 100644
--- a/src/lib/stream/rc4/rc4.cpp
+++ b/src/lib/stream/rc4/rc4.cpp
@@ -113,4 +113,8 @@ void RC4::clear()
 */
 RC4::RC4(size_t s) : m_SKIP(s) {}
 
+void RC4::seek(u64bit)
+   {
+   throw Exception("RC4 does not support seeking");
+   }
 }
diff --git a/src/lib/stream/rc4/rc4.h b/src/lib/stream/rc4/rc4.h
index f166a2772..88798fae6 100644
--- a/src/lib/stream/rc4/rc4.h
+++ b/src/lib/stream/rc4/rc4.h
@@ -39,6 +39,8 @@ class BOTAN_DLL RC4 final : public StreamCipher
       explicit RC4(size_t skip = 0);
 
       ~RC4() { clear(); }
+
+      void seek(u64bit offset) override;
    private:
       void key_schedule(const byte[], size_t) override;
       void generate();
diff --git a/src/lib/stream/salsa20/salsa20.cpp b/src/lib/stream/salsa20/salsa20.cpp
index 1d3fe3d28..f11fe5e59 100644
--- a/src/lib/stream/salsa20/salsa20.cpp
+++ b/src/lib/stream/salsa20/salsa20.cpp
@@ -227,4 +227,8 @@ void Salsa20::clear()
    m_position = 0;
    }
 
+void Salsa20::seek(u64bit)
+   {
+   throw Not_Implemented("Salsa20::seek");
+   }
 }
diff --git a/src/lib/stream/salsa20/salsa20.h b/src/lib/stream/salsa20/salsa20.h
index 7e75470da..8256ea4db 100644
--- a/src/lib/stream/salsa20/salsa20.h
+++ b/src/lib/stream/salsa20/salsa20.h
@@ -33,6 +33,8 @@ class BOTAN_DLL Salsa20 final : public StreamCipher
       void clear() override;
       std::string name() const override;
       StreamCipher* clone() const override { return new Salsa20; }
+
+      void seek(u64bit offset) override;
    private:
       void key_schedule(const byte key[], size_t key_len) override;
 
diff --git a/src/lib/stream/stream_cipher.h b/src/lib/stream/stream_cipher.h
index bff1fd1a6..56bd2d5d9 100644
--- a/src/lib/stream/stream_cipher.h
+++ b/src/lib/stream/stream_cipher.h
@@ -80,6 +80,12 @@ class BOTAN_DLL StreamCipher : public SymmetricAlgorithm
       */
       virtual StreamCipher* clone() const = 0;
 
+      /**
+      * Set the offset and the state used later to generate the keystream
+      * @param offset the offset where we begin to generate the keystream
+      */
+      virtual void seek(u64bit offset) = 0;
+
       StreamCipher();
       virtual ~StreamCipher();
    };