diff --git a/src/base_32.ml b/src/base_32.ml
new file mode 100644
index 00000000..5c111967
--- /dev/null
+++ b/src/base_32.ml
@@ -0,0 +1,24 @@
+(* TODO test *)
+(* Crockford's variant of Base32
+   http://www.crockford.com/wrmg/base32.html
+   except that:
+     - 'U' is not excluded but also decodes to 'V'
+     - '-' is not allowed
+     - checksum is not allowed *)
+
+(* 'I' 'L' 'O' 'U' excluded *)
+let alphabet = Base32.make_alphabet "0123456789ABCDEFGHJKMNPQRSTVWXYZ"
+let encode s = Base32.encode_string ~alphabet s
+
+let decode s =
+  let s =
+    String.map
+      (fun c ->
+        match Char.uppercase_ascii c with
+        | 'O' -> '0'
+        | 'I' | 'L' -> '1'
+        | 'U' -> 'V'
+        | c -> c)
+      s
+  in
+  Base32.decode ~alphabet ~off:0 ~len:(String.length s) s
diff --git a/src/dune b/src/dune
index 19e30781..d9a560ea 100644
--- a/src/dune
+++ b/src/dune
@@ -21,6 +21,11 @@
  (modules syntax)
  (libraries))
 
+(library
+ (name base_32)
+ (modules base_32)
+ (libraries base32))
+
 (rule
  (target assets_crunch.ml)
  (deps