src/Pure/General/sha1.ML

 signature SHA1 =
 sig
   eqtype digest
   val digest: string -> digest
   val rep: digest -> string
+  val fake: string -> digest
 end;
 
 structure SHA1: SHA1 =
 struct
 

 datatype digest = Digest of string;
 
 val digest = Digest o digest_string;
 fun rep (Digest s) = s;
 
+val fake = Digest;
+
 end;