aenker is a simple commandline utility to encrypt files to a public key (Curve25519) with an
authenticated encryption scheme (ChaCha20Poly1305). This is basically an ECIES.
The input is split into smaller chunks internally and is encrypted & authenticated individually. Padding and concatenation is done similarly to InterMAC. The key used for encryption is derived with HKDF using Blake2b after performing anonymous Diffie-Hellman with a given public and a random ephemeral private key. All this is further described in the specification.
Authenticated encryption authenticates the ciphertext upon decryption and combined with the above construction any chunk reordering, bit-flips or even truncation can be detected and are shown as errors. Only ciphertext that has been successfully decrypted and authenticated is ever written to the output. The chunking still alleviates the need to fit the entire file into memory at once or do two passes over all data. Thus you can also encrypt files of many gigabytes.
See the disclaimer below. Even though I took a number of courses on information security
and cryptography, I would not call myself a cryptographer.
If you're looking for a modern and well-vetted encryption tool, you should take a look at
age instead.
I believe aenker was started before age existed but the latter has seen much more development.
go get -u github.com/ansemjo/aenker
Download a release from GitHub (replace
$VERSION with the desired release):
curl -Lo aenker https://github.com/ansemjo/aenker/releases/download/$VERSION/aenker-linux-amd64
chmod +x aenker
./aenker --help
Download a tarball from GitHub and
use the included makefile to build a static binary and embed proper version information:
cd aenker-master/
make
make install PREFIX=~/.local
First, you need a keypair. To generate a new random keypair use the builtin keygenerator:
aenker keygen [-f where/to/store/seckey]
Without any arguments, this will store the key in the default location ~/.local/share/aenker/aenkerkey
and your public key will be printed to the terminal. Send your public key to anyone who wants to
encrypt data for you and keep your private key .. well, private.
If you want to display your public key later or calculate the public key to a given private key, you
can use the subcommand show:
aenker show [-k path/to/seckey]
Note: aenker only performs anonymous Diffie-Hellman and the keys are not signed or certified. To protect against man-in-the-middle attacks you should transfer the key over a secure channel or verify the integrity on a different channel.
Encrypt a simple message using the public key with the subcommand seal:
echo 'Hello, World!' | aenker seal -p lGLD...AFBo= > message.ae
Decrypt messages with the open subcommand. If your key is stored at the default location you can
decrypt a message by simply piping the encrypted message into aenker:
aenker open [-k path/to/seckey] < message.ae
Input and output files can be specified with the -i and -o flags respectively. The terms seal
and open are commonly used in the context of AEADs but you can also use their aliases encrypt
and decrypt if you prefer:
aenker decrypt -i documents.tar.ae -k mykey | tar -xf -
The key flags -p/--peer and -k/--key accept the base64-encoded keys on the commandline or
the name of a file which contains the key alone on one line. Specifically, the first match to the
regular expression /^[A-Za-z0-9+/]{43}=$/ is used, so you can add as many comments as you like to
your key files.
Specifying the key on the commandline is convenient for public keys but should be avoided for private keys:
... | aenker seal -p lGLDUgFvp8TSwJ17VC9k0/T9mNWvfGoJ42zauMkAFBo= > message.ae
Generally, Curve25519 - and thus aenker - accepts any 32 byte value as a key. You could generate a private key by any other means and then only calculate the public key to distribute it. Possibilities include:
- reading 32 bytes of system randomness from
/dev/urandom - use an implementation of Argon2i to derive a key from a password, i.e. ansemjo/stdkdf
- ...
All of the commands output a nicely formatted help message, so you can use help at any time:
aenker help
If you prefer, you can instead install and read manpages with:
aenker docs man -d ~/.local/share/man/
man aenker
Completion scripts for your shell can be generated and sourced with:
. <(aenker docs completion)
Append this piece to your ~/.magic file:
0 string aenker\xe7\x9e aenker encrypted file
!:mime application/octet-stream
And file(1) should detect encrypted files as aenker encrypted file.
Please be advised that I am not a professional cryptographer. This is merely a hobby of mine which I hope can be useful to you.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.