perf: use iv_len method for iv length comparsion

OpenSSL::Cipher#iv_len returns the expected length in bytes for an IV for this Cipher.

Author: rubysamurai

lib/cryptology.rb

@@ -30,15 +30,15 @@ def self.encrypt_data(data, key, cipher, iv)
     c = OpenSSL::Cipher.new(cipher)
     c.encrypt
     c.key = key
-    c.iv  = iv unless iv.length != c.random_iv.length
+    c.iv = iv if iv.length == c.iv_len
     c.update(data) + c.final
   end
 
   def self.decrypt_data(data, key, cipher, iv)
     decipher = OpenSSL::Cipher.new(cipher)
     decipher.decrypt
     decipher.key = key
-    decipher.iv  = iv unless iv.length != decipher.random_iv.length
+    decipher.iv  = iv if iv.length == decipher.iv_len
     decipher.update(data) + decipher.final
   end