Add HKDF-Expand-Label

Step 1/n of TLS 1.3

3 files changed, 62 insertions, 2 deletions

diff --git a/src/lib/kdf/hkdf/hkdf.cpp b/src/lib/kdf/hkdf/hkdf.cpp
index 20215125b..d66847244 100644
--- a/src/lib/kdf/hkdf/hkdf.cpp
+++ b/src/lib/kdf/hkdf/hkdf.cpp
@@ -1,6 +1,6 @@
 /*
 * HKDF
-* (C) 2013,2015 Jack Lloyd
+* (C) 2013,2015,2017 Jack Lloyd
 * (C) 2016 René Korthaus, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
@@ -73,4 +73,50 @@ size_t HKDF_Expand::kdf(uint8_t key[], size_t key_len,
    return offset;
    }
 
+secure_vector<uint8_t>
+hkdf_expand_label(const std::string& hash_fn,
+                  const uint8_t secret[], size_t secret_len,
+                  const std::string& label,
+                  const uint8_t hash_val[], size_t hash_val_len,
+                  size_t length)
+   {
+   if(length > 0xFFFF)
+      throw Invalid_Argument("HKDF-Expand-Label requested output too large");
+   if(label.size() > 0xFF)
+      throw Invalid_Argument("HKDF-Expand-Label label too long");
+   if(hash_val_len > 0xFF)
+      throw Invalid_Argument("HKDF-Expand-Label hash too long");
+
+   auto mac = MessageAuthenticationCode::create("HMAC(" + hash_fn + ")");
+   if(!mac)
+      throw Invalid_Argument("HKDF-Expand-Label with HMAC(" + hash_fn + ") not available");
+
+   HKDF_Expand hkdf(mac.release());
+
+   secure_vector<uint8_t> output(length);
+   std::vector<uint8_t> prefix(3 + label.size() + 1);
+
+   prefix[0] = get_byte<uint16_t>(0, length);
+   prefix[1] = get_byte<uint16_t>(1, length);
+   prefix[2] = static_cast<uint8_t>(label.size());
+
+   copy_mem(prefix.data() + 3,
+            reinterpret_cast<const uint8_t*>(label.data()),
+            label.size());
+
+   prefix[3 + label.size()] = static_cast<uint8_t>(hash_val_len);
+
+   /*
+   * We do something a little dirty here to avoid copying the hash_val,
+   * making use of the fact that Botan's KDF interface supports label+salt,
+   * and knowing that our HKDF hashes first param label then param salt.
+   */
+   hkdf.kdf(output.data(), output.size(),
+            secret, secret_len,
+            hash_val, hash_val_len,
+            prefix.data(), prefix.size());
+
+   return output;
+   }
+
 }
diff --git a/src/lib/kdf/hkdf/hkdf.h b/src/lib/kdf/hkdf/hkdf.h
index e63973497..7d2b7f8b2 100644
--- a/src/lib/kdf/hkdf/hkdf.h
+++ b/src/lib/kdf/hkdf/hkdf.h
@@ -86,6 +86,20 @@ class BOTAN_PUBLIC_API(2,0) HKDF_Expand final : public KDF
       std::unique_ptr<MessageAuthenticationCode> m_prf;
    };
 
+/**
+* HKDF-Expand-Label from TLS 1.3/QUIC
+* @param label the full label (no "TLS 1.3, " or "tls13 " prefix
+*  is applied)
+*/
+secure_vector<uint8_t>
+BOTAN_PUBLIC_API(2,3) hkdf_expand_label(
+   const std::string& hash_fn,
+   const uint8_t secret[], size_t secret_len,
+   const std::string& label,
+   const uint8_t hash_val[], size_t hash_val_len,
+   size_t length);
+
+
 }
 
 #endif
diff --git a/src/lib/kdf/hkdf/info.txt b/src/lib/kdf/hkdf/info.txt
index db6618c3c..b9b17b3b8 100644
--- a/src/lib/kdf/hkdf/info.txt
+++ b/src/lib/kdf/hkdf/info.txt
@@ -1,3 +1,3 @@
 <defines>
-HKDF -> 20131128
+HKDF -> 20170927
 </defines>