package cryptodbm

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Encrypted layer over the dbm library: access to serverless, key-value databases with symmetric encryption.


Dune Dependency






cryptodbm is an OCaml library that provides an encrypted layer over the dbm library: access to serverless, key-value databases with symmetric encryption.


Install with opam: opam install cryptodbm

API Documentation

The Cryptodbm API. See also the examples/ dir.

The ocamlfind package name is cryptodbm.


This library provides an encrypted layer on top of the Dbm and Cryptokit packages. The improvements over Dbm are:

  • A single database file may contain several independent subtables, identified by a name (a string).

  • Each subtable can be signed and encrypted individually, or encrypted using a global password.

  • The whole file can be signed.

  • Obfuscating data is -optionally- appended to keys, data, and to the whole table, so that two databases with the same content look significantly different, once encrypted.

  • Encryption is symmetric: encryption and decryption both use the same password.

  • Signature is symmetric: signing and verifying the signature both use the same signword.

As a quick example, the following uncrypted bindings (key => data):

        "john-doe"        => "age 36"
        "some secret"     => "The cake is a lie."
        "Motto"           => "For relaxing times, make it Suntory time"

are stored as follows in the encrypted file (with variations depending on the password, the salt, and other parameters):

 [^.2] => [...F...).Hsl..tB]
 [...y;....~.:.6V.2] => [....I...JR..w.E9..G..q=...K....b]
 [..'.C...F.x.3K.y2] => [1.)]
 [S.....5 Y....8..2] => [.D........2..u...q.......}Z.b..z.zo.}.l3l.....>.]
 [...xD;@.8..wV..P1....e}....u..`.2] => [hb..2.._B....Y?0....|.....tM....]
 [K.#i.7j..H.ZZ.^.2] => [..z....,........] v}

Including several subtables in the same database file avoids having to deal with multiple files to store related information, and also prevents information leak through the number and sizes of a set of database files.

This library was primarily designed to store encrypted exam files on a university server. A common layout consists in several subtables encrypted with a global password, as well as an uncrypted subtable containing (public) meta-information.

Typical example

   let table = open_append ~file:"/path/to/myfile" ~passwd:"my-secret-passwd" in

   let subtable = append_subtable table ~name:"here the subtable name" () in

   add subtable ~key:"key1" ~data:"data1" () ;
   add subtable ~key:"key2" ~data:"data2" () ;

   close table ;


Didier Le Botlan, github.lebotlan@dfgh.met where you replace .met by .net.