Support seeking in Salsa20

Add a test that StreamCipher::seek throws if not keyed.

6 files changed, 23 insertions, 9 deletions

diff --git a/src/lib/stream/chacha/chacha.cpp b/src/lib/stream/chacha/chacha.cpp
index 52e5eaaf4..0f1e082cf 100644
--- a/src/lib/stream/chacha/chacha.cpp
+++ b/src/lib/stream/chacha/chacha.cpp
@@ -222,10 +222,7 @@ std::string ChaCha::name() const
 
 void ChaCha::seek(uint64_t offset)
    {
-   if (m_state.size() == 0 && m_buffer.size() == 0)
-      {
-      throw Invalid_State("You have to setup the stream cipher (key and iv)");
-      }
+   verify_key_set(m_state.empty() == false);
 
    // Find the block offset
    uint64_t counter = offset / 64;
diff --git a/src/lib/stream/ctr/ctr.cpp b/src/lib/stream/ctr/ctr.cpp
index 463119caf..21e62fb4b 100644
--- a/src/lib/stream/ctr/ctr.cpp
+++ b/src/lib/stream/ctr/ctr.cpp
@@ -174,6 +174,8 @@ void CTR_BE::add_counter(const uint64_t counter)
 
 void CTR_BE::seek(uint64_t offset)
    {
+   verify_key_set(m_iv.empty() == false);
+
    const uint64_t base_counter = m_ctr_blocks * (offset / m_counter.size());
 
    zeroise(m_counter);
diff --git a/src/lib/stream/ofb/ofb.cpp b/src/lib/stream/ofb/ofb.cpp
index 5a2d63dd4..75b7048aa 100644
--- a/src/lib/stream/ofb/ofb.cpp
+++ b/src/lib/stream/ofb/ofb.cpp
@@ -66,6 +66,6 @@ void OFB::set_iv(const uint8_t iv[], size_t iv_len)
 
 void OFB::seek(uint64_t)
    {
-   throw Exception("OFB does not support seeking");
+   throw Not_Implemented("OFB does not support seeking");
    }
 }
diff --git a/src/lib/stream/rc4/rc4.cpp b/src/lib/stream/rc4/rc4.cpp
index 60565d445..cce09d183 100644
--- a/src/lib/stream/rc4/rc4.cpp
+++ b/src/lib/stream/rc4/rc4.cpp
@@ -115,6 +115,6 @@ RC4::RC4(size_t s) : m_SKIP(s) {}
 
 void RC4::seek(uint64_t)
    {
-   throw Exception("RC4 does not support seeking");
+   throw Not_Implemented("RC4 does not support seeking");
    }
 }
diff --git a/src/lib/stream/salsa20/info.txt b/src/lib/stream/salsa20/info.txt
index 3c7fed8fe..8e9bfa568 100644
--- a/src/lib/stream/salsa20/info.txt
+++ b/src/lib/stream/salsa20/info.txt
@@ -1,3 +1,3 @@
 <defines>
-SALSA20 -> 20131128
+SALSA20 -> 20171114
 </defines>
diff --git a/src/lib/stream/salsa20/salsa20.cpp b/src/lib/stream/salsa20/salsa20.cpp
index 3f93cee94..ce22adcb7 100644
--- a/src/lib/stream/salsa20/salsa20.cpp
+++ b/src/lib/stream/salsa20/salsa20.cpp
@@ -234,8 +234,23 @@ void Salsa20::clear()
    m_position = 0;
    }
 
-void Salsa20::seek(uint64_t)
+void Salsa20::seek(uint64_t offset)
    {
-   throw Not_Implemented("Salsa20::seek");
+   verify_key_set(m_state.empty() == false);
+
+   // Find the block offset
+   const uint64_t counter = offset / 64;
+   uint8_t counter8[8];
+   store_le(counter, counter8);
+
+   m_state[8]  = load_le<uint32_t>(counter8, 0);
+   m_state[9] += load_le<uint32_t>(counter8, 1);
+
+   salsa20(m_buffer.data(), m_state.data());
+
+   ++m_state[8];
+   m_state[9] += (m_state[8] == 0);
+
+   m_position = offset % 64;
    }
 }