Add StreamCipher::default_iv_length

2 files changed, 6 insertions, 2 deletions

diff --git a/src/lib/stream/chacha/chacha.cpp b/src/lib/stream/chacha/chacha.cpp
index 7ccc4293b..fac9a5a36 100644
--- a/src/lib/stream/chacha/chacha.cpp
+++ b/src/lib/stream/chacha/chacha.cpp
@@ -310,7 +310,7 @@ void ChaCha::seek(uint64_t offset)
    verify_key_set(m_state.empty() == false);
 
    // Find the block offset
-   uint64_t counter = offset / 64;
+   const uint64_t counter = offset / 64;
 
    uint8_t out[8];
 
diff --git a/src/lib/stream/chacha/chacha.h b/src/lib/stream/chacha/chacha.h
index a4f3e3b75..d0e131315 100644
--- a/src/lib/stream/chacha/chacha.h
+++ b/src/lib/stream/chacha/chacha.h
@@ -34,11 +34,15 @@ class BOTAN_PUBLIC_API(2,0) ChaCha final : public StreamCipher
       void set_iv(const uint8_t iv[], size_t iv_len) override;
 
       /*
-      * ChaCha accepts 0, 8, or 12 byte IVs. The default IV is a 8 zero bytes.
+      * ChaCha accepts 0, 8, 12 or 24 byte IVs.
+      * The default IV is a 8 zero bytes.
       * An IV of length 0 is treated the same as the default zero IV.
+      * An IV of length 24 selects XChaCha mode
       */
       bool valid_iv_length(size_t iv_len) const override;
 
+      size_t default_iv_length() const override { return 24; }
+
       Key_Length_Specification key_spec() const override
          {
          return Key_Length_Specification(16, 32, 16);