From 509c6116a8e5ba2a15c57f9346a695b2b6480fc2 Mon Sep 17 00:00:00 2001
From: Jeffrey Walton <noloader@gmail.com>
Date: Mon, 2 Apr 2018 14:41:37 -0400
Subject: [PATCH] Update documentation

---
 scrypt.cpp | 2 +-
 scrypt.h   | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/scrypt.cpp b/scrypt.cpp
index 34b0532f..f84939a6 100644
--- a/scrypt.cpp
+++ b/scrypt.cpp
@@ -254,6 +254,7 @@ size_t Scrypt::DeriveKey(byte*derived, size_t derivedLen, const byte*secret, siz
     // http://stackoverflow.com/q/49604260/608639
     #pragma omp parallel
     {
+        // Each thread gets its own copy
         AlignedSecByteBlock XY(static_cast<size_t>(blockSize * 256U));
         AlignedSecByteBlock  V(static_cast<size_t>(blockSize * cost * 128U));
 
@@ -267,7 +268,6 @@ size_t Scrypt::DeriveKey(byte*derived, size_t derivedLen, const byte*secret, siz
         }
     }
 
-
     // 5: DK <-- PBKDF2(P, B, 1, dkLen)
     PBKDF2_SHA256(derived, derivedLen, secret, secretLen, B, B.size(), 1);
 
diff --git a/scrypt.h b/scrypt.h
index d8ab7d8a..4d4dfcd9 100644
--- a/scrypt.h
+++ b/scrypt.h
@@ -19,6 +19,11 @@
 NAMESPACE_BEGIN(CryptoPP)
 
 /// \brief Scrypt key derivation function
+/// \details The Crypto++ implementation uses OpenMP to accelerate the derivation when
+///   available.
+/// \details The Crypto++ implementation of Scrypt is limited by C++ datatypes. For
+///   example, the library is limited to a derived key length of <tt>SIZE_MAX</tt>,
+///   and not <tt>(2^32 - 1) * 32</tt>.
 /// \sa <A HREF="https://www.tarsnap.com/scrypt/scrypt.pdf">Stronger Key Derivation via
 ///   Sequential Memory-Hard Functions</a>,
 ///   <A HREF="https://www.tarsnap.com/scrypt.html">The scrypt key derivation function</A>
@@ -74,6 +79,9 @@ public:
     ///   integer less than or equal to <tt>((2^32-1) * 32) / (128 * r)</tt>.
     /// \details Scrypt always returns 1 because it only performs 1 iteration. Other
     ///   derivation functions, like PBKDF's, will return more interesting values.
+    /// \details The Crypto++ implementation of Scrypt is limited by C++ datatypes. For
+    ///   example, the library is limited to a derived key length of <tt>SIZE_MAX</tt>,
+    ///   and not <tt>(2^32 - 1) * 32</tt>.
     size_t DeriveKey(byte *derived, size_t derivedLen, const byte *secret, size_t secretLen,
         const byte *salt, size_t saltLen, word64 cost=2, word64 blockSize=8, word64 parallelization=1) const;