8 files changed, 61 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;
    }
 }
diff --git a/src/tests/data/stream/salsa20.vec b/src/tests/data/stream/salsa20.vec
index afe111266..e8276bf32 100644
--- a/src/tests/data/stream/salsa20.vec
+++ b/src/tests/data/stream/salsa20.vec
@@ -30,3 +30,27 @@ Key = 3070F0DB09C523507D36404DAC79038A393E9F0E3CF5F870B16D2A06DA68DCD3
 In = F4EA120B47D15466ADE07DF0F2FF508759D9CB1035CEEAB43920E9094FA50B868673B07173557D4B994B1E9D35078C1C7369DF6B6ADB2EC0E6BFD280FEA8AC31DB44BEB0C2A4DDC6198957BD0592E3E587D304863B893FF8EEE0EFC70CED5D712651C3E9DD1A0DE0480FD8CCCBAE4C50DCCBACB83DCDC3E2CEF7DBC645F0AF468163FB0E015EF48AD74694DFBCE2DB8430A6E91645FD16ADBB72E21A0FBAEDF5ECFF829CEA9CBC22F82902748AA52DA5CE903D9F2BDE77EFEF5FA3970C720E89F25DD05157247BF0DE2D2129C3F856238D4FAD
 Nonce = 4AFE87BF79EB938D786BA54C26FD6D7E62261EEAE8B62202
 Out = 46F396F0D2D54189968BF56B5B2F35588C3AD851E00FAC6507598F3EA0193A586C00B18677811CC305B0261D9AEBBB9C0485A5800C940AA4F09C4FBDEDE12553824C429C7954E0B8DAD889203D292517B98A64E8D7A37C1364EB0934751323D9B9F8498F50D729E977FB742880222F22AC5D7BFEBE6905A4C344D82027398A70C334635792DEB0F20B83861B05E731F5627AEE17DF20413C79957556E66A970085E9AD40A73D9A964381584976C6F111619A916FBB5F5D305DF862D5A56BAC9FF9B436F31C85F34FF890B5AD3299EDA2B8642D
+
+Key = 000102030405060708090A0B0C0D0E0F
+Nonce = 0000000000000000
+Seek = 3
+Out = F7BA2B20F76802410C688688895AD8C1BD4EA6C9B140FB9B90E21049BF583F527970EBC1
+
+Key = 0F62B5085BAE0154A7FA4DA0F34699EC3F92E5388BDE3184D72A7DD02376C91C
+Nonce = 288FF65DC42B92F9
+Out = 5E5E71F90199340304ABB22A37B6625BF883FB89CE3B21F54A10B81066EF87DA30B77699AA7379DA595C77DD59542DA208E5954F89E40EB7AA80A84A6176663F
+
+Key = 0F62B5085BAE0154A7FA4DA0F34699EC3F92E5388BDE3184D72A7DD02376C91C
+Nonce = 288FF65DC42B92F9
+Seek = 65472
+Out = 2DA2174BD150A1DFEC1796E921E9D6E24ECF0209BCBEA4F98370FCE629056F64917283436E2D3F45556225307D5CC5A565325D8993B37F1654195C240BF75B16
+
+Key = 0F62B5085BAE0154A7FA4DA0F34699EC3F92E5388BDE3184D72A7DD02376C91C
+Nonce = 288FF65DC42B92F9
+Seek = 65473
+Out = A2174BD150A1DFEC1796E921E9D6E24ECF0209BCBEA4F98370FCE629056F64917283436E2D3F45556225307D5CC5A565325D8993B37F1654195C240BF75B16ABF39A
+
+Key = 0F62B5085BAE0154A7FA4DA0F34699EC3F92E5388BDE3184D72A7DD02376C91C
+Nonce = 288FF65DC42B92F9
+Seek = 65479
+Out = DFEC1796E921E9D6E24ECF0209BCBEA4F98370FCE629056F64917283436E2D3F45556225307D5CC5A565325D8993B37F1654195C240BF75B16ABF39A210EEE89598B7133377056C2FE
diff --git a/src/tests/test_stream.cpp b/src/tests/test_stream.cpp
index c430c0cf3..ab9de228b 100644
--- a/src/tests/test_stream.cpp
+++ b/src/tests/test_stream.cpp
@@ -68,6 +68,20 @@ class Stream_Cipher_Tests final : public Text_Based_Test
                result.test_success("Trying to encrypt with no key set fails");
                }
 
+            try
+               {
+               cipher->seek(0);
+               result.test_failure("Was able to seek without a key being set");
+               }
+            catch(Botan::Invalid_State&)
+               {
+               result.test_success("Trying to seek with no key set fails");
+               }
+            catch(Botan::Not_Implemented&)
+               {
+               result.test_success("Trying to seek failed because not implemented");
+               }
+
             cipher->set_key(key);
 
             if(nonce.size())