diff --git a/lib/moab/file_signature.rb b/lib/moab/file_signature.rb
index ec4d6588..a41bf1f7 100644
--- a/lib/moab/file_signature.rb
+++ b/lib/moab/file_signature.rb
@@ -65,33 +65,28 @@ def initialize(opts = {})
     # @return [String] The SHA256 checksum value of the file
     attribute :sha256, String, :on_save => Proc.new { |n| n.nil? ? "" : n.to_s }
 
-    ALL_CHECKSUM_ALGOS = {
+    KNOWN_ALGOS = {
       md5: proc { Digest::MD5.new },
       sha1: proc { Digest::SHA1.new },
       sha256: proc { Digest::SHA2.new(256) }
     }.freeze
 
     def self.from_file(pathname, algos_to_use = nil)
-      algos_to_use ||= ALL_CHECKSUM_ALGOS.keys
+      if algos_to_use
+        raise 'Unrecognized algorithm requested' unless algos_to_use.all? { |a| KNOWN_ALGOS.include?(a) }
+      else
+        algos_to_use = KNOWN_ALGOS.keys
+      end
 
-      computed_signatures = algos_to_use.map do |algo_name|
-        [algo_name, ALL_CHECKSUM_ALGOS[algo_name].call]
-      end.to_h
+      signatures = algos_to_use.map { |k| [k, KNOWN_ALGOS[k].call] }.to_h
 
       pathname.open("r") do |stream|
         while (buffer = stream.read(8192))
-          computed_signatures.each_value do |digest|
-            digest.update(buffer)
-          end
+          signatures.each_value { |digest| digest.update(buffer) }
         end
       end
 
-      file_signature = new(size: pathname.size)
-      computed_signatures.each do |algo_name, digest|
-        file_signature.instance_variable_set("@#{algo_name}", digest.hexdigest)
-      end
-
-      file_signature
+      new(signatures.map { |k, digest| [k, digest.hexdigest] }.to_h.merge(size: pathname.size) )
     end
 
     # @param type [Symbol,String] The type of checksum