Added Extended Hash-Based Signatures (XMSS)

[1] XMSS: Extended Hash-Based Signatures,
    draft-itrf-cfrg-xmss-hash-based-signatures-06
    Release: July 2016.
    https://datatracker.ietf.org/doc/
    draft-irtf-cfrg-xmss-hash-based-signatures/?include_text=1

Provides XMSS_PublicKey and XMSS_PrivateKey classes as well as implementations
for the Botan interfaces PK_Ops::Signature and PK_Ops::Verification. XMSS has
been integrated into the Botan test bench, signature generation and verification
can be tested independently by invoking "botan-test xmss_sign" and
"botan-test xmss_verify"

- Some headers that are not required to be exposed to users of the library have
  to be declared as public in `info.txt`. Declaring those headers private will
  cause the amalgamation build to fail. The following headers have been
  declared public inside `info.txt`, even though they are only intended for
  internal use:
    * atomic.h
    * xmss_hash.h
    * xmss_index_registry.h
    * xmss_address.h
    * xmss_common_ops.h
    * xmss_tools.h
    * xmss_wots_parameters.h
    * xmss_wots_privatekey.h
    * xmss_wots_publickey.h

- XMSS_Verification_Operation Requires the "randomness" parameter out of the
  XMSS signature. "Randomness" is part of the prefix that is hashed *before*
  the message. Since the signature is unknown till sign() is called, all
  message content has to be buffered. For large messages this can be
  inconvenient or impossible.

  **Possible solution**: Change PK_Ops::Verification interface to take
  the signature as constructor argument, and provide a setter method to be able
  to update reuse the instance on multiple signatures. Make sign a parameterless
  member call. This solution requires interface changes in botan.

  **Suggested workaround** for signing large messages is to not sign the message
  itself, but to precompute the message hash manually using Botan::HashFunctio
  and sign the message hash instead of the message itself.

- Some of the available test vectors for the XMSS signature verification have
  been commented out in order to reduce testbench runtime.

1 files changed, 111 insertions, 0 deletions

diff --git a/src/lib/pubkey/xmss/xmss_tools.h b/src/lib/pubkey/xmss/xmss_tools.h
new file mode 100644
index 000000000..07e36ea71
--- /dev/null
+++ b/src/lib/pubkey/xmss/xmss_tools.h
@@ -0,0 +1,111 @@
+/**
+ * XMSS Address
+ * (C) 2016 Matthias Gierlings
+ *
+ * Botan is released under the Simplified BSD License (see license.txt)
+ **/
+
+#ifndef BOTAN_XMSS_TOOLS_H__
+#define BOTAN_XMSS_TOOLS_H__
+
+#include <stdint.h>
+#include <iterator>
+#include <type_traits>
+#include <botan/types.h>
+#include <botan/secmem.h>
+
+namespace Botan {
+
+/**
+ * Helper tools for low level byte operations required
+ * for the XMSS implementation.
+ **/
+ class XMSS_Tools
+   {
+   public:
+      XMSS_Tools(const XMSS_Tools&) = delete;
+      void operator=(const XMSS_Tools&) = delete;
+
+      static const XMSS_Tools& get();
+
+      /**
+       * Retrieves information about endianess
+       *
+       * @return true if machine uses little-endian byte order, false
+       *         otherwise.
+       **/
+      inline bool is_little_endian() const { return m_is_little_endian; }
+
+      /**
+       * Concatenates the byte representation in big-endian order of any
+       * integral value to a secure_vector.
+       *
+       * @param target Vector to concatenate the byte representation of the
+       *               integral value to.
+       * @param src integral value to concatenate.
+       **/
+      template<typename T,
+               typename U = typename std::enable_if<std::is_integral<T>::value,
+                                                    void>::type>
+      void concat(secure_vector<byte>& target, const T& src) const;
+
+      /**
+       * Concatenates the last n bytes of the byte representation in big-endian
+       * order of any integral value to a to a secure_vector.
+       *
+       * @param target Vector to concatenate the byte representation of the
+       *               integral value to.
+       * @param src Integral value to concatenate.
+       * @param len number of bytes to concatenate. This value must be smaller
+       *            or equal to the size of type T.
+       **/
+      template <typename T,
+                typename U = typename std::enable_if<std::is_integral<T>::value,
+                void>::type>
+      void concat(secure_vector<byte>& target, const T& src, size_t len) const;
+
+   private:
+      XMSS_Tools();
+
+      bool m_is_little_endian;
+   };
+
+template <typename T, typename U>
+void XMSS_Tools::concat(secure_vector<byte>& target, const T& src) const
+   {
+   const byte* src_bytes = reinterpret_cast<const byte*>(&src);
+   if(is_little_endian())
+      std::reverse_copy(src_bytes,
+                        src_bytes + sizeof(src),
+                        std::back_inserter(target));
+   else
+      std::copy(src_bytes,
+                src_bytes + sizeof(src),
+                std::back_inserter(target));
+   }
+
+
+template <typename T, typename U>
+void XMSS_Tools::concat(secure_vector<byte>& target,
+                        const T& src,
+                        size_t len) const
+   {
+   size_t c = static_cast<size_t>(std::min(len, sizeof(src)));
+   if(len > sizeof(src))
+      {
+      target.resize(target.size() + len - sizeof(src), 0);
+      }
+
+   const byte* src_bytes = reinterpret_cast<const byte*>(&src);
+   if(is_little_endian())
+      std::reverse_copy(src_bytes,
+                        src_bytes + c,
+                        std::back_inserter(target));
+   else
+      std::copy(src_bytes + sizeof(src) - c,
+                src_bytes + sizeof(src),
+                std::back_inserter(target));
+   }
+}
+
+#endif