make libsodium optional

bin/minisign

@@ -31,6 +31,13 @@ rescue OptionParser::InvalidOption
   exit 1
 end
 
+if options[:G] || options[:R] || options[:G] || options[:S]
+  unless defined? RbNaCl::Hash
+    STDERR.puts "Error: libsodium is not installed!"
+    exit 1
+  end
+end
+
 Minisign::CLI.generate(options) if options[:G]
 Minisign::CLI.recreate(options) if options[:R]
 Minisign::CLI.change_password(options) if options[:C]

lib/minisign.rb

@@ -2,12 +2,18 @@
 
 require 'ed25519'
 require 'base64'
-require 'rbnacl'
+require 'openssl'
+begin
+    require 'rbnacl'
+rescue LoadError => e
+    # errors handled when invoked (see Minisign::NaCl)
+end
 
 require 'minisign/cli'
 require 'minisign/utils'
 require 'minisign/public_key'
 require 'minisign/signature'
 require 'minisign/private_key'
 require 'minisign/key_pair'
+require 'minisign/nacl'
 require 'minisign/error'

lib/minisign/error.rb

@@ -9,4 +9,7 @@ class PasswordMissingError < StandardError
 
   class PasswordIncorrectError < StandardError
   end
+
+  class LibSodiumDependencyError < StandardError
+  end
 end

lib/minisign/nacl.rb

@@ -0,0 +1,27 @@
+module Minisign
+    module NaCl
+        def self.safely
+            begin
+                yield
+            rescue NameError
+                raise Minisign::LibSodiumDependencyError, 'libsodium is not installed!'
+            end
+        end
+        module Hash
+            module Blake2b
+                def self.digest(*args)
+                    NaCl::safely do
+                        RbNaCl::Hash::Blake2b.digest(*args)
+                    end
+                end
+            end
+        end
+        module PasswordHash
+            def self.scrypt(*args)
+                NaCl::safely do
+                    RbNaCl::PasswordHash.scrypt(*args)
+                end
+            end
+        end
+    end
+end

lib/minisign/utils.rb

@@ -4,11 +4,11 @@ module Minisign
   # Helpers used in multiple classes
   module Utils
     def blake2b256(message)
-      RbNaCl::Hash::Blake2b.digest(message, { digest_size: 32 })
+      Minisign::NaCl::Hash::Blake2b.digest(message, { digest_size: 32 })
     end
 
     def blake2b512(message)
-      RbNaCl::Hash::Blake2b.digest(message, { digest_size: 64 })
+      OpenSSL::Digest.new('blake2b512').digest(message)
     end
 
     # @return [Array<32 bit unsigned ints>]
@@ -25,7 +25,7 @@ def hex(bytes)
 
     # @return [String] the <kdf_output> used to xor the ed25519 keys
     def derive_key(password, kdf_salt, kdf_opslimit, kdf_memlimit)
-      RbNaCl::PasswordHash.scrypt(
+      Minisign::NaCl::PasswordHash.scrypt(
         password,
         kdf_salt,
         kdf_opslimit,