4 files changed, 20 insertions, 12 deletions
diff --git a/src/lib/pubkey/xmss/info.txt b/src/lib/pubkey/xmss/info.txt
index bab541625..862ff68f9 100644
--- a/src/lib/pubkey/xmss/info.txt
+++ b/src/lib/pubkey/xmss/info.txt
@@ -42,4 +42,5 @@ xmss_verification_operation.h
 asn1
 rng
 hash
+sha2_32
 </requires>
diff --git a/src/lib/pubkey/xmss/xmss_hash.cpp b/src/lib/pubkey/xmss/xmss_hash.cpp
index d6ae2bb3b..3731f7751 100644
--- a/src/lib/pubkey/xmss/xmss_hash.cpp
+++ b/src/lib/pubkey/xmss/xmss_hash.cpp
@@ -8,6 +8,7 @@
  **/
 
 #include <botan/xmss_hash.h>
+#include <botan/exceptn.h>
 
 namespace Botan {
 
@@ -16,14 +17,19 @@ XMSS_Hash::XMSS_Hash(const XMSS_Hash& hash)
    {
    }
 
-XMSS_Hash::XMSS_Hash(const std::string& h_func_name)
-   : m_hash(HashFunction::create(h_func_name)),
-     m_msg_hash(HashFunction::create(h_func_name)),
-     m_output_length(m_hash->output_length()),
-     m_zero_padding(m_output_length - 1, 0x00),
-     m_hash_func_name(h_func_name)
+XMSS_Hash::XMSS_Hash(const std::string& h_func_name) :
+   m_hash_func_name(h_func_name),
+   m_hash(HashFunction::create(h_func_name))
    {
+   if(!m_hash)
+      throw Lookup_Error("XMSS cannot use hash " + h_func_name +
+                         " because it is unavailable");
+
+   m_output_length = m_hash->output_length();
    BOTAN_ASSERT(m_output_length > 0, "Hash output length of zero is invalid.");
+
+   m_zero_padding.resize(m_output_length - 1);
+   m_msg_hash.reset(m_hash->clone());
    }
 
 void
diff --git a/src/lib/pubkey/xmss/xmss_hash.h b/src/lib/pubkey/xmss/xmss_hash.h
index cf42f8d91..2cca26658 100644
--- a/src/lib/pubkey/xmss/xmss_hash.h
+++ b/src/lib/pubkey/xmss/xmss_hash.h
@@ -147,17 +147,18 @@ class XMSS_Hash
       size_t output_length() const { return m_output_length; };
 
    private:
+      static const byte m_id_f = 0x00;
+      static const byte m_id_h = 0x01;
+      static const byte m_id_hmsg = 0x02;
+      static const byte m_id_prf = 0x03;
+
+      const std::string m_hash_func_name;
       std::unique_ptr<HashFunction> m_hash;
       std::unique_ptr<HashFunction> m_msg_hash;
       size_t m_output_length;
 
       //32 byte id prefixes prepended to the hash input.
       std::vector<byte> m_zero_padding;
-      static const byte m_id_f = 0x00;
-      static const byte m_id_h = 0x01;
-      static const byte m_id_hmsg = 0x02;
-      static const byte m_id_prf = 0x03;
-      const std::string m_hash_func_name;
    };
 
 }
diff --git a/src/lib/pubkey/xmss/xmss_parameters.cpp b/src/lib/pubkey/xmss/xmss_parameters.cpp
index c55b25a27..cc4d923dd 100644
--- a/src/lib/pubkey/xmss/xmss_parameters.cpp
+++ b/src/lib/pubkey/xmss/xmss_parameters.cpp
@@ -43,7 +43,7 @@ XMSS_Parameters::xmss_algorithm_t XMSS_Parameters::xmss_id_from_string(const std
       return XMSS_SHAKE256_W16_H16;
    if(param_set == "XMSS_SHAKE256_W16_H20")
       return XMSS_SHAKE256_W16_H20;
-   throw Invalid_Argument("Unknown XMSS algorithm param '" + param_set + "'");
+   throw Lookup_Error("Unknown XMSS algorithm param '" + param_set + "'");
    }
 
 XMSS_Parameters::XMSS_Parameters(const std::string& param_set)