Add full HKDF implementation

Adds the full HKDF as class HKDF, renames the existing HKDF,
which only implemented the expansion step, to HKDF_Expand
and adds the extraction step as HKDF_Extract.

The latter two are usually only used seperately in
protocols such as TLS. A normal user would go for the
full HKDF.

1 files changed, 41 insertions, 4 deletions

diff --git a/src/lib/kdf/hkdf/hkdf.cpp b/src/lib/kdf/hkdf/hkdf.cpp
index 13d5832d2..f44ed81bd 100644
--- a/src/lib/kdf/hkdf/hkdf.cpp
+++ b/src/lib/kdf/hkdf/hkdf.cpp
@@ -1,6 +1,7 @@
 /*
 * HKDF
 * (C) 2013,2015 Jack Lloyd
+* (C) 2016 René Korthaus, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
@@ -9,18 +10,54 @@
 
 namespace Botan {
 
-size_t HKDF::kdf(byte out[], size_t out_len,
+size_t HKDF::kdf(byte key[], size_t key_len,
                  const byte secret[], size_t secret_len,
                  const byte salt[], size_t salt_len,
                  const byte label[], size_t label_len) const
    {
+   HKDF_Extract extract(m_prf->clone());
+   HKDF_Expand expand(m_prf->clone());
+   secure_vector<byte> prk(m_prf->output_length());
+
+   extract.kdf(prk.data(), prk.size(), secret, secret_len, salt, salt_len, nullptr, 0);
+   return expand.kdf(key, key_len, prk.data(), prk.size(), nullptr, 0, label, label_len);
+   }
+
+size_t HKDF_Extract::kdf(byte key[], size_t key_len,
+                         const byte secret[], size_t secret_len,
+                         const byte salt[], size_t salt_len,
+                         const byte[], size_t) const
+   {
+   secure_vector<byte> prk;
+   if(salt_len == 0)
+      {
+      m_prf->set_key(std::vector<byte>(m_prf->output_length()));
+      }
+   else
+      {
+      m_prf->set_key(salt, salt_len);
+      }
+
+   m_prf->update(secret, secret_len);
+   m_prf->final(prk);
+
+   const size_t written = std::min(prk.size(), key_len);
+   copy_mem(&key[0], prk.data(), written);
+   return written;
+   }
+
+size_t HKDF_Expand::kdf(byte key[], size_t key_len,
+                        const byte secret[], size_t secret_len,
+                        const byte salt[], size_t salt_len,
+                        const byte label[], size_t label_len) const
+   {
    m_prf->set_key(secret, secret_len);
 
    byte counter = 1;
    secure_vector<byte> h;
    size_t offset = 0;
 
-   while(offset != out_len && counter != 0)
+   while(offset != key_len && counter != 0)
       {
       m_prf->update(h);
       m_prf->update(label, label_len);
@@ -28,8 +65,8 @@ size_t HKDF::kdf(byte out[], size_t out_len,
       m_prf->update(counter++);
       m_prf->final(h);
 
-      const size_t written = std::min(h.size(), out_len - offset);
-      copy_mem(&out[offset], h.data(), written);
+      const size_t written = std::min(h.size(), key_len - offset);
+      copy_mem(&key[offset], h.data(), written);
       offset += written;
       }