April 11, 2025
      
                  
        
  Author(s)
  Yu Long  Chen,   Michael  Davidson,   Morris  Dworkin,   John  Kelsey,   Yu  Sasaki,   Meltem  Sonmez Turan,   Alyssa  Thompson,   Nicky  Mouha,   Donghoon  Chang
 
       
            
    
    
        This report introduces the cryptographic accordion as a tweakable, variable-input-length strong pseudorandom permutation (VIL-SPRP) that is constructed from an underlying block cipher. An accordion facilitates the cryptographic processing of messages of