AKT Tool

NAME

akt - Tool to protect your sensitive data with secure storage

SYNOPSIS

akt [ -v ] [-vv] [-vv] [-V] [ -c config-file ] [-t count ] [-z] command [-k file ] [ -d dir ] [ -p password ] [--password password ] [--passfile file ] [--passenv name ] [--passfd fd ] [--passask] [--passcmd cmd ] [--wallet-key-file file ]

DESCRIPTION

akt is a tool to store information in secure wallets and protect the stored information by encrypting the content. It is necessary to know one of the wallet password to access its content. akt can be used to safely store passwords, credentials, bank accounts and even documents.

Wallets are protected by a master key using AES-256 and the wallet master key is protected by a user password. The wallet defines up to 7 slots that identify a password key that is able to unlock the master key. To open a wallet, it is necessary to unlock one of these 7 slots by providing the correct password. Wallet key slots are protected by the user's password and the PBKDF2-HMAC-256 algorithm, a random salt, a random counter and they are encrypted using AES-256.

Values stored in the wallet are protected by their own encryption keys using AES-256. A wallet can contain another wallet which is then protected by its own encryption keys and passwords (with 7 independent slots). Because the child wallet has its own master key, it is necessary to known the primary password and the child password to unlock the parent wallet first and then the child wallet.

The data is organized in blocks of 4K whose primary content is encrypted either by the wallet master key or by the entry keys. The data block is signed by using HMAC-256. A data block can contain several values but each of them is protected by its own encryption key. Each value is also signed using HMAC-256. Large values can be written to several data blocks and in that case each fragment is encrypted by using its own encryption key.

The tool provides several commands that allow to create a keystore, insert values, retrieve values or delete them. You can use it to store your passwords, your secret keys and even your documents.

Passwords are retrieved using one of the following options:

  • by reading a file that contains the password,
  • by looking at an environment variable,
  • by using a command line argument,
  • by getting the password through the ssh-askpass(1) external command,
  • by running an external command,
  • by asking interactively the user for the password,
  • by asking through a network socket for the password.

OPTIONS

The following options are recognized by akt:

-V Prints the akt version.

-v Enable the verbose mode.

-vv Enable debugging output.

-c config-file Defines the path of the global akt configuration file.

-t count Defines the number of threads for the encryption and decryption process. By default, it uses the number of system CPU cores.

-k file

Specifies the path of the keystore file to open.

-d directory

Specifies the directory path of the keystore data files. When this option is used, the data blocks are written in separate files. The data blocks do not contain the encryption keys and each of them is encrypted with its own secure key.

-p password

The keystore password is passed within the command line. Using this method is convenient but is not safe.

--passenv envname

The keystore password is passed within an environment variable with the given name. Using this method is considered safer but still provides some security leaks.

--passfile path

The keystore password is passed within a file that is read. The file must not be readable or writable by other users or group: its mode must be r??------. The directory that contains the file must also satisfy the not readable by other users or group members, This method is safer.

--passfd fd

The keystore password is passed within a pipe whose file descriptor number is given. The file descriptor is read to obtain the password. This method is safer.

--passask

The keystore password is retrieved by the running the external tool ssh-askpass(1) which will ask the password through either KDE, Gnome or another desktop interactive application. The password is retrieved through a pipe that akt sets while launching the command.

--passcmd cmd

The keystore password is retrieved by the running the external command defined in cmd. The command should print the password on its standard output without end of line. The password is retrieved through a pipe that akt sets while launching the command.

--wallet-key-file file Defines the path of a file which contains the wallet master key file.

-z Erase and fill with zeros instead of random values.

COMMANDS

The create command

akt create keystore.akt [--force] [--counter-range min:max] [--split count] [--gpg user ...]

Create a new keystore and protect it with the password. When the keystore file already exist, the create operation will fail unless the --force option is passed.

The password to protect the wallet is passed using one of the following options: --passfile , --passenv , --password , --passsocket or --gpg. When none of these options are passed, the password is asked interactively.

The --counter-range option allows to control the range for the random counter used by PBKDF2 to generate the encryption key derived from the specified password. High values provide a strongest derived key at the expense of speed. This option is ignored when the --gpg option is used.

The --split option indicates to use several separate files for the data blocks and it controls the number of separate files to use. When used, a directory with the name of the keystore file is created and will contain the data files.

The --gpg option allows to protect the keystore by using a user's GPG encryption key. The option argument defines the GPG user's name or GPG key. When the keystore password is protected by the user's GPG key, a random password is generated to protect the keystore. The gpg2(1) command is used to encrypt that password using the user's public key and save it in the keystore header. The gpg2(1) command is then used to decrypt that and be able to unlock the keystore provided that the user's private key is known. When using the --gpg option, it is possible to protect the keystore for several users, thus being able to share the secure file with each of them.

The extract command

akt extract keystore.akt -- name
akt extract keystore.akt {name...}

This command allows to extract files or directories recursively from the keystore. It is possible to extract several files and directories at the same time.

When the -- option is passed, the command accepts only one argument. It extracts the specified name and writes the result on the standard output. It can be used as a target for a pipe command.

The mount command

akt mount keystore.akt [-f] [--enable-cache] mount-point

This command is available when the fuse(8) support is enabled. It allows to mount the keystore content on the mount-point directory and access the encrypted content through the filesystem. The akt tool works as a daemon to serve fuse(8) requests that come from the kernel. The -f option allows to run this daemon as a foreground process. By default, the kernel cache are disabled because the keystore content is decrypted and given as clear content to the kernel. This could be a security issue for some system and users. The kernel cache can be enabled by using the --enable-cache option.

To unmount the file system, one must use the mount(8) command.

umount mount-point

The set command

akt set keystore.akt name value

The set command is used to store a content passed as command line argument in the wallet. If the wallet already contains the name, the value is updated.

The store command

akt store keystore.akt -- name
akt store keystore.akt {file...|directory...}

This command can store files or directories recursively in the keystore. It is possible to store several files and directories at the same time.

When the -- option is passed, the command accepts only one argument. It reads the standard input and stores it under the specified name. It can be used as a target for a pipe command.

The remove command

akt remove keystore.akt name ...

The remove command is used to erase a content from the wallet. The data block that contained the content to protect is erased and replaced by zeros. The secure key that protected the wallet entry is also cleared. It is possible to remove several contents.

The edit command

akt edit keystore.akt [-e editor] name

The edit command can be used to edit the protected wallet entry by calling the user's prefered editor with the content. The content is saved in a temporary directory and in a temporary file. The editor is launched with the path and when editing is finished the temporary file is read. The temporary directory and files are erased when the editor terminates successfully or not. The editor can be specified by using the -e option, by setting up the EDITOR environment variable or by updating the editor(1) alternative with update-alternative(1).

The list command

akt list keystore.akt

The list command describes the entries stored in the keystore with their name, size, type, creation date and number of keys which protect the entry.

The get command

akt get keystore.akt [-n] name...

The get command allows to retrieve the value associated with a wallet entry. It retrieves the value for each name passed to the command. The value is printed on the standard output. By default a newline is emitted after each value. The -n option prevents the output of the trailing newline.

The password-add command

akt password-add keystore.akt [--new-passfile file] [--new-password password] [--new-passenv name]

The password-add command allows to add a new password in one of the wallet key slot. Up to seven passwords can be defined to protect the wallet. The overall security of the wallet is that of the weakest password. To add a new password, one must know an existing password.

The password-remove command

akt password-remove keystore.akt [--force]

The password-remove command can be used to erase a password from the wallet master key slots. Removing the last password makes the keystore unusable and it is necessary to pass the --force option for that.

The password-set command

akt password-set [--new-passfile file] [--new-password password] [--new-passenv name]

The password-set command allows to change the current wallet password.

SECURITY

Wallet master keys are protected by a derived key that is created from the user's password using PBKDF2 and HMAC-256 as hashing operation. When the wallet is first created, a random salt and counter are allocated which are then used by the PBKDF2 generation. The wallet can be protected by up to 7 different passwords. Despite this, the security of the wallet master key still depends on the strength of the user's password. For this matter, it is still critical for the security to use long passphrases.

The passphrase can be passed within an environment variable or within a command line argument. These two methods are considered unsafe because it could be possible for other processes to see these values. It is best to use another method such as using the interactive form, passing the password through a file or passing using a socket based communication.

When the wallet master key is protected using gpg2(1) a 32-bytes random binary key and a 16-bytes random binary IV is created to protect the wallet master key. Another set of 80 bytes of random binary data is used to encrypt and sign the whole wallet master key block. The 128 bytes that form these random binary keys are encrypted using the user's GPG public key and the result saved in the keystore header block. The --gpg option is specified only for the creation of the keystore and allows to encrypt a master key slot for several GPG keys. To unlock the keystore file, the gpg2(1) command will be used to decrypt the keystore header content automatically. When the user's GPG private key is not found, it is not possible to unlock the keystore with this method.

When several GPG keys are used to protect the wallet, they share the same 80 bytes to decrypt the wallet master key block but they have their own key and IV to unlock the key slot.

Depending on the size, a data stored in the wallet is split in one or several data entry. Each wallet data entry is then protected by their own secret key and IV vector. Wallet data entry are encrypted using AES-256-CBC. The wallet data entry key and IV vectors are protected by the wallet master key.

When the --split option is used, the data storage files only contain the data blocks. They do not contain any encryption key. The data storage files use the .dkt file extension.

CONFIGURATION

The akt global configuration file contains several configuration properties which are used to customize several commands. These properties can be modified with the config command.

gpg-encrypt

This property defines the gpg2(1) command to be used to encrypt a content. The content to encrypt is passed in the standard input and the encrypted content is read from the standard output. The GPG key parameter can be retrieved by using the $USER pattern.

gpg-decrypt

This property defines the gpg2(1) command to be used to decrypt a content. The content to decrypt is passed in the standard input and the decrypted content is read from the standard output.

gpg-list-keys

This property defines the gpg2(1) command to be used to retrieve the list of available secret keys. This command is executed when the keystore file is protected by a GPG key to identify the possible GPG Key ids that are capable of decrypting it.

fill-zero

This property controls whether akt must fill unused data areas with zeros or with random bytes.

SEE ALSO

editor(1), update-alternative(1), ssh-askpass(1), gpg2(1), mount(8), fuse(8)

AUTHOR

Written by Stephane Carrez.