From e0ea31bd2e73ca2fae56a3b89a50d91e6e74c962 Mon Sep 17 00:00:00 2001
From: Didactic Drunk <1479616+didactic-drunk@users.noreply.github.com>
Date: Thu, 27 Jun 2019 16:52:45 -0700
Subject: [PATCH] Swap Kdf subkey_size and subkey_id arguments.

---
 README.md            | 10 +++++-----
 spec/cox/kdf_spec.cr |  8 ++++----
 src/cox/kdf.cr       |  2 +-
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/README.md b/README.md
index 2019030..12ffd21 100644
--- a/README.md
+++ b/README.md
@@ -131,11 +131,11 @@ output = d.hexdigest
 ```crystal
 kdf = Cox::Kdf.new
 
-# kdf.derive(8_byte_context, subkey_size, subkey_id)
-subkey1 = kdf.derive "context1", 16, 0
-subkey2 = kdf.derive "context1", 16, 1
-subkey3 = kdf.derive "context2", 32, 0
-subkey4 = kdf.derive "context2", 64, 1
+# kdf.derive(8_byte_context, subkey_id, subkey_size)
+subkey1 = kdf.derive "context1", 0, 16
+subkey2 = kdf.derive "context1", 1, 16
+subkey3 = kdf.derive "context2", 0, 32
+subkey4 = kdf.derive "context2", 1, 64
 ```
 
 ### Password Hashing
diff --git a/spec/cox/kdf_spec.cr b/spec/cox/kdf_spec.cr
index 35bbdfe..a8675a1 100644
--- a/spec/cox/kdf_spec.cr
+++ b/spec/cox/kdf_spec.cr
@@ -10,15 +10,15 @@ describe Cox::Kdf do
     kdf2 = Cox::Kdf.from_base64 kdf1.to_base64
 
     # verify generated subkey's are the same after loading
-    key1_s1 = kdf1.derive CONTEXT, 16, 0
-    key2_s1 = kdf2.derive CONTEXT, 16, 0
+    key1_s1 = kdf1.derive CONTEXT, 0, 16
+    key2_s1 = kdf2.derive CONTEXT, 0, 16
     key1_s1.should eq key2_s1
   end
 
   it "generates different keys" do
     kdf1 = Cox::Kdf.new
-    subkey1 = kdf1.derive CONTEXT, 16, 0
-    subkey2 = kdf1.derive CONTEXT, 16, 1
+    subkey1 = kdf1.derive CONTEXT, 0, 16
+    subkey2 = kdf1.derive CONTEXT, 1, 16
     subkey1.should_not eq subkey2
   end
 
diff --git a/src/cox/kdf.cr b/src/cox/kdf.cr
index 5d333b7..37ee384 100644
--- a/src/cox/kdf.cr
+++ b/src/cox/kdf.cr
@@ -16,7 +16,7 @@ module Cox
 
     # context must be 8 bytes
     # subkey_size must be 16..64 bytes as of libsodium 1.0.17
-    def derive(context, subkey_size, subkey_id = 0)
+    def derive(context, subkey_id, subkey_size)
       if context.bytesize != LibSodium::KDF_CONTEXT_SIZE
         raise ArgumentError.new("context must be #{LibSodium::KDF_CONTEXT_SIZE}, got #{context.bytesize}")
       end