iterate on LMS's PseudorandomKeyGeneration

randombit · Apr 8, 2024 · 114c35e · 114c35e
1 parent fe06610
commit 114c35e
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Showing 2 changed files with 13 additions and 12 deletions.
diff --git a/src/lib/pubkey/hss_lms/hss_lms_utils.cpp b/src/lib/pubkey/hss_lms/hss_lms_utils.cpp
@@ -11,14 +11,16 @@
 #include <botan/internal/stl_util.h>
 
 namespace Botan {
-PseudorandomKeyGeneration::PseudorandomKeyGeneration(std::span<const uint8_t> identifier) :
-      m_input_buffer(identifier.size() + sizeof(uint32_t) + sizeof(uint16_t) + sizeof(uint8_t)),
-      m_q(m_input_buffer.data() + identifier.size(), sizeof(uint32_t)),
-      m_i(m_input_buffer.data() + identifier.size() + sizeof(uint32_t), sizeof(uint16_t)),
-      m_j(m_input_buffer.data() + identifier.size() + sizeof(uint32_t) + sizeof(uint16_t), sizeof(uint8_t))
 
-{
-   copy_mem(m_input_buffer.data(), identifier.data(), identifier.size());
+// The magic numbers in the initializer list below reflect the structure of the
+// m_input_buffer member and must be updated if any of the pre-defined
+// std::span<>s are changed.
+PseudorandomKeyGeneration::PseudorandomKeyGeneration(std::span<const uint8_t> identifier) :
+      m_input_buffer(identifier.size() + 7),
+      m_q(std::span(m_input_buffer).last<7>().first<4>()),
+      m_i(std::span(m_input_buffer).last<3>().first<2>()),
+      m_j(std::span(m_input_buffer).last<1>()) {
+   copy_into(std::span(m_input_buffer).first(identifier.size()), identifier);
 }
 
 void PseudorandomKeyGeneration::gen(std::span<uint8_t> out, HashFunction& hash, std::span<const uint8_t> seed) const {

diff --git a/src/lib/pubkey/hss_lms/hss_lms_utils.h b/src/lib/pubkey/hss_lms/hss_lms_utils.h
@@ -35,25 +35,24 @@ class PseudorandomKeyGeneration {
       /**
        * @brief Specify the value for the u32str(q) hash input field
        */
-      void set_q(uint32_t q) { store_be(q, m_q.data()); }
+      void set_q(uint32_t q) { store_be(m_q, q); }
 
       /**
        * @brief Specify the value for the u16str(i) hash input field
        */
-      void set_i(uint16_t i) { store_be(i, m_i.data()); }
+      void set_i(uint16_t i) { store_be(m_i, i); }
 
       /**
        * @brief Specify the value for the u8str(j) hash input field
        */
-      void set_j(uint8_t j) { m_j[0] = j; }
+      void set_j(uint8_t j) { store_be(m_j, j); }
 
       /**
        * @brief Create a hash value using the preconfigured prefix and a @p seed
        */
       template <concepts::resizable_byte_buffer T = secure_vector<uint8_t>>
       T gen(HashFunction& hash, std::span<const uint8_t> seed) const {
-         T output;
-         output.resize(hash.output_length());
+         T output(hash.output_length());
          gen(output, hash, seed);
          return output;
       }