Basic password manager library and command-line application in OCaml
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README.md

Work-in-progress: PassMenage Build Status

This is a password manager library implementing basic operations on a data structure that can be used to store passwords.

We're still working on the library, so things may change, and there may be BUGS.

Cmdliner application

An example implementation using Cmdliner is provided in [./app/passmenage_cli.ml].

The binary provides the following sub-commands:

COMMANDS
       add
           Add an entry to a category.

       get
           Get an entry from the password file.

       init
           Initialize a new password file

       list
           List categories, or entries in a specific category

       pretty-print
           Pretty-print the state (INCLUDING PASSWORDS)

A manpage is available with ./passmenage_cli.native --help

Data structures

The internal data structure is a JSON tree:

{ /* encrypted, OCaml struct name: `state` */
  configuration:
  [ /* list of string tuples, OCaml struct name: `configuration` */
    ["entry 1", "value 1"],
    ["entry 2", "value 2"],
  ],

  categories: /* list of associative dictionaries, which may be nested */
  [
    { /* OCaml struct name: `category` */
      /* each category may optionally be encrypted with a separate key */
      name: "category 1",
      entries: /* list of associative dictionaries */
        [
          { /* OCaml struct name: `entry` */
            name: "my github password",
            passphrase: "123456",
            metadata:
              [ /* list of string tuples */
                ["url", "https://github.com/signin"],
                ["last_changed", "2017-12-01"],
              ]
          },
        ],
      subcategories: [] /* a list of `category` objects */
    },
  ]
}

The tree is always encrypted when serialized. Each category may be independently encrypted to give the user control over the date loaded in memory during a given session.

The encryption is performed using Nocrypto's AES-CCM primitive with a 128-bit MAC , a random 256-bit key, and a random 104-bit nonce. New random values for the key and nonce are generated on each serialization/encryption. I couldn't find any documentation that references a standardized instance of AES-CCM in nocrypto, so there's no telling what actually goes on under the hood inside this library without reading the source code, which I'm not smart enough to understand. YOLO.

The random key is encrypted with the scrypt_enc_buf(maxmem = 1MB, maxtime = 1 second) primitive from Tarsnap (a KDF based on HMAC-SHA-256 and AES-CTR-256) using a user-provided passphrase, and the result is stored in a JSON object:

{ /* OCaml struct name: `encrypted_data` */
  kdf: "scrypt...", /* the output from scrypt_enc_buf() */

  nonce: "AAAAAA", /* 32-byte random value */

  ciphertext: "BBBBBB", /* ciphertext and MAC from AES-CCM */
}

Using the library

The mli interface specification contains most of the information needed to use the library.

A nice HTML representation can be generated using topkg doc if you have the topkg-care package installed from opam.

TODO

  • figure out what breed of AES-CCM nocrypto implements
  • add version information to the state structure
  • add version information to the encrypted_data structure
  • ensure key/name uniqueness
    • on configuration and metadata lists
    • on entries and categories
    • consider not exposing raw structs to enforce this invariant
  • provide UPSERT and similar helper functions to operate on the data