cmdsafe

cmdsafe

cmdsafe is a small utility to store CLI commands with sensitive arguments, like passphrases, in an encrypted format. These commands can then be executed with those arguments automatically appended - plus any additional arguments passed to the run command - without having to manually copy the passphrase from a separate password manager.

Getting Started

Installing

With Go (Golang) installed on your machine, run the following command to download, build and install the tool:

go get github.com/aleist/cmdsafe

Usage

Command Overview

$ cmdsafe 
Usage: cmdsafe [global flags ...] command [flags ...]

Global flags:
  -db path
        The database path (default "data.db")

The commands are:
  delete        delete a saved command
  list          list all saved commands
  print         print a command configuration to stdout
  run           run a saved command
  save          save a new or update an existing command

This shows the subcommands used to save, run and manage command configurations. Each command configuration is given a name, which itself is not encrypted and should therefore not contain any sensitive information. This is used as a handle for the actual executable name (e.g. sshpass) and arguments. This also means that multiple different configurations can be saved for a given executable.

Saving a command configuration

$ cmdsafe save
Usage: save [-r] -name <name> <cmd> [<cmd args> ...]
  -name string
        The name used to refer to the saved cmd
  -r    Replace existing entry with the given name

Example: Save a non-interactive, password-based SSH login using sshpass and ssh under the name "server1":

$ cmdsafe save -name server1 sshpass -p secret ssh -p 2022 [email protected]

Note that it is more secure to use public key based authentication with SSH when possible.

Running a command

$ cmdsafe run
Usage: run [-d] <cmd name> [<cmd args> ...]
  -d    Run the command in detached mode

Additional command arguments not stored with the command configuration can be passed to cmdsafe run and will be appended to the arguments from the configuration when the command is invoked.

Example: Run the SSH command we saved above:

$ cmdsafe run server1
Enter password: 

Listing all command configurations

$ cmdsafe list
server1
server2

Printing a command

$ cmdsafe print
Usage: print <cmd name>

Deleting a command

$ cmdsafe delete
Usage: delete <cmd name>

Security

The following describes the steps used to secure each command configuration:

1. The command with its arguments is encrypted using a 256 bit AES-CTR (counter mode) stream cipher with randomly generated encryption key and initialisation vector.
2. The unique encryption key from step 1 is itself encrypted with a key derived from the user password using the memory-hard scrypt key derivation function. The encryption function is again 256 bit AES-CTR.
3. An SHA256 based HMAC using a second scrypt derived key from the user password is used to sign all stored data to ensure integrity and authenticity: the two initialisation vectors, the encryption key (from step 1) ciphertext, the command configuration ciphertext, and an identifier for the encryption algorithm.

Note that this does not prevent the secret from showing up in the active process list and potentially other places while the command is running, so this should not be used on systems where that may be a concern. It only protects the command configuration and thus any secret contained therein at rest.