Use crypto_box_beforenmbytes to precompute CryptoBox shared key.

examples/constants.cr

@@ -7,6 +7,11 @@ require "../src/sodium"
 {% end %}
 puts ""
 
+{% for name in %w(MAC_SIZE NM_SIZE) %}
+  puts "Sodium::CryptoBox::{{ name.id }} #{Sodium::CryptoBox::{{ name.id }}}"
+{% end %}
+puts ""
+
 {% for name in %w(KEY_SIZE SEED_SIZE SIG_SIZE) %}
   puts "Sodium::Sign::SecretKey::{{ name.id }} #{Sodium::Sign::SecretKey::{{ name.id }}}"
 {% end %}

src/sodium/crypto_box.cr

@@ -4,17 +4,27 @@ require "./crypto_box/secret_key"
 require "./nonce"
 
 module Sodium
+  # Use Sodium::CryptoBox::SecretKey#box
   class CryptoBox
     include Wipe
 
     MAC_SIZE = LibSodium.crypto_box_macbytes.to_i
+    # :nodoc:
+    NM_SIZE = LibSodium.crypto_box_beforenmbytes.to_i
+    raise "NM_SIZE=#{NM_SIZE}, assumed it was 32" if NM_SIZE != 32
 
-    # BUG: precompute size
     @[Wipe::Var]
-    @bytes = Bytes.new(1)
+    @key = StaticArray(UInt8, 32).new 0
 
+    # :nodoc:
+    # Used by SecretKey#box
     def initialize(@secret_key : SecretKey, @public_key : PublicKey)
-      # TODO: precompute using crypto_box_beforenm
+      # Precalculate key for later use.
+      # Large speed gains with small data sizes and many messages.
+      # Small speed gains with large data sizes or few messages.
+      if LibSodium.crypto_box_beforenm(@key, @public_key.to_slice, @secret_key.to_slice) != 0
+        raise Error.new("crypto_box_beforenm")
+      end
     end
 
     # Encrypts data and returns {ciphertext, nonce}
@@ -26,7 +36,7 @@ module Sodium
     #
     # Optionally supply a destination buffer.
     def encrypt(src : Bytes, dst = Bytes.new(src.bytesize + MAC_SIZE), nonce = Nonce.new) : {Bytes, Nonce}
-      if LibSodium.crypto_box_easy(dst, src, src.bytesize, nonce.to_slice, @public_key.to_slice, @secret_key.to_slice) != 0
+      if LibSodium.crypto_box_easy_afternm(dst, src, src.bytesize, nonce.to_slice, @key.to_slice) != 0
         raise Error.new("crypto_box_easy")
       end
       {dst, nonce}
@@ -41,8 +51,8 @@ module Sodium
     # Returns decrypted message.
     #
     # Optionally supply a destination buffer.
-    def decrypt(src : Bytes, dst = Bytes.new(src.bytesize - MAC_SIZE), nonce = Nonce.new) : Bytes
-      if LibSodium.crypto_box_open_easy(dst, src, src.bytesize, nonce.to_slice, @public_key.to_slice, @secret_key.to_slice) != 0
+    def decrypt(src : Bytes, dst = Bytes.new(src.bytesize - MAC_SIZE), nonce = Nonce.random) : Bytes
+      if LibSodium.crypto_box_open_easy_afternm(dst, src, src.bytesize, nonce.to_slice, @key) != 0
         raise Error::DecryptionFailed.new("crypto_box_open_easy")
       end
       dst

src/sodium/crypto_box/secret_key.cr

@@ -5,8 +5,6 @@ require "../crypto_box"
 
 class Sodium::CryptoBox
   # Key used for encryption + authentication or encryption without authentication, not for unencrypted signing.
-  #
-  # If you don't want this behavior pass a duplicate of the key/seed to initialize().
   class SecretKey < Key
     KEY_SIZE  = LibSodium.crypto_box_secretkeybytes.to_i
     SEED_SIZE = LibSodium.crypto_box_seedbytes.to_i

src/sodium/lib_sodium.cr

@@ -12,6 +12,7 @@ module Sodium
     fun crypto_box_noncebytes : LibC::SizeT
     fun crypto_box_sealbytes : LibC::SizeT
     fun crypto_box_macbytes : LibC::SizeT
+    fun crypto_box_beforenmbytes : LibC::SizeT
     fun crypto_sign_publickeybytes : LibC::SizeT
     fun crypto_sign_secretkeybytes : LibC::SizeT
     fun crypto_sign_bytes : LibC::SizeT
@@ -148,22 +149,45 @@ module Sodium
       secret_key_output : Pointer(LibC::UChar)
     ) : LibC::Int
 
-    fun crypto_box_easy(
-      output : Pointer(LibC::UChar),
-      data : Pointer(LibC::UChar),
-      data_size : LibC::ULongLong,
-      nonce : Pointer(LibC::UChar),
-      recipient_public_key : Pointer(LibC::UChar),
-      sender_secret_key : Pointer(LibC::UChar)
+    fun crypto_box_beforenm(
+      k : Pointer(LibC::UChar),
+      pk : Pointer(LibC::UChar),
+      sk : Pointer(LibC::UChar)
     ) : LibC::Int
 
-    fun crypto_box_open_easy(
+    fun crypto_box_easy_afternm(
       output : Pointer(LibC::UChar),
       data : Pointer(LibC::UChar),
       data_size : LibC::ULongLong,
       nonce : Pointer(LibC::UChar),
-      sender_public_key : Pointer(LibC::UChar),
-      recipient_secret_key : Pointer(LibC::UChar)
+      key : Pointer(LibC::UChar)
+    ) : LibC::Int
+
+    # TODO: possibly remove after switching to detached
+    fun crypto_box_open_easy_afternm(
+      output : Pointer(LibC::UChar),
+      data : Pointer(LibC::UChar),
+      data_size : LibC::ULongLong,
+      nonce : Pointer(LibC::UChar),
+      key : Pointer(LibC::UChar)
+    ) : LibC::Int
+
+    fun crypto_box_detached_afternm(
+      output : Pointer(LibC::UChar),
+      mac : Pointer(LibC::UChar),
+      data : Pointer(LibC::UChar),
+      data_size : LibC::ULongLong,
+      nonce : Pointer(LibC::UChar),
+      key : Pointer(LibC::UChar)
+    ) : LibC::Int
+
+    fun crypto_box_open_detached_afternm(
+      output : Pointer(LibC::UChar),
+      data : Pointer(LibC::UChar),
+      mac : Pointer(LibC::UChar),
+      data_size : LibC::ULongLong,
+      nonce : Pointer(LibC::UChar),
+      key : Pointer(LibC::UChar)
     ) : LibC::Int
 
     fun crypto_box_seal(
@@ -294,8 +318,7 @@ module Sodium
     end
   end
 
-  # Constant time memory compare.
-  # Raises unless comparison succeeds.
+  # Constant time memory compare.  Raises unless comparison succeeds.
   def self.memcmp!(a, b)
     raise Error::MemcmpFailed.new unless memcmp(a, b)
     true

src/sodium/secure_buffer.cr

@@ -2,12 +2,12 @@ require "./lib_sodium"
 require "./wipe"
 
 module Sodium
+  # Allocate guarded memory using [sodium_malloc](https://libsodium.gitbook.io/doc/memory_management)
   class SecureBuffer
     getter bytesize
 
     delegate :+, :[], :[]=, to: to_slice
 
-    # Allocate guarded memory using [sodium_malloc](https://libsodium.gitbook.io/doc/memory_management)
     def initialize(@bytesize : Int32)
       @ptr = LibSodium.sodium_malloc @bytesize
     end

src/sodium/sign/secret_key.cr

@@ -3,15 +3,15 @@ require "../key"
 require "./public_key"
 
 module Sodium
-  # Key used for signing/verification only.
+  # Ed25519 secret key used for signing.
   #
-  # If you don't want this behavior pass a duplicate of the key/seed to initialize().
+  # [https://libsodium.gitbook.io/doc/public-key_cryptography/public-key_signatures](https://libsodium.gitbook.io/doc/public-key_cryptography/public-key_signatures)
   #
   # Usage:
   # ```
-  # key = SecretKey.new
+  # key = Sodium::Sign::SecretKey.new
   # sig = key.sign_detached data
-  # key.public_key.verify_detached data
+  # key.public_key.verify_detached data, sig
   # ```
   class Sign::SecretKey < Sodium::Key
     KEY_SIZE  = LibSodium.crypto_sign_secretkeybytes.to_i