Add README and license.

LICENSE

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+Copyright (c) 2020 Érico Nogueira
+
+Permission to use, copy, modify, and distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

README.md

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+# get-otp
+
+This repository holds a combination of tools that can be used to (comfortably)
+generate TOTP 2FA access tokens on the desktop, instead of depending on a phone
+app.
+
+## get-otp
+
+Main tool, depends on:
+
+- [jq](https://stedolan.github.io/jq/)
+- [fzf](https://github.com/junegunn/fzf)
+- [OATH Toolkit](https://www.nongnu.org/oath-toolkit/)
+- [wl-clipboard](https://github.com/bugaevc/wl-clipboard) (optional)
+
+It will use the `cbc-file` executable from this project to decrypt a
+`~/.local/share/otp_accounts` file, whose decrypted contents should be in the
+same format as exported by [andOTP](https://github.com/andOTP/andOTP). It can
+then run a menu, using `fzf`, to let you choose the account for which you want
+an access token. If running on Wayland, the token will also be copied to the
+clipboard.
+
+```
+$ get-otp [account_name]
+```
+
+## encrypt-otp
+
+This tool doesn't depend on anything besides `cbc-file`. What it does is encrypt
+the file passed to it (which should be in the format exported by andOTP, as
+mentioned above) and put the encrypted file in the correct place.
+
+```
+$ encrypt-otp otp_accounts.json
+```
+
+## cbc-file
+
+Hidden utility, does the encryption magic. Despite the name, uses
+[ChaCha20+Poly1305](https://tools.ietf.org/html/rfc7539) for encryption, as
+implemented by [BearSSL](https://www.bearssl.org/), together with
+[argon2](https://github.com/p-h-c/phc-winner-argon2) for key derivation.
+
+Both of the mentioned libraries are necessary for building this utility. On
+Linux, a kernel which implements the
+[getrandom(2)](https://man.voidlinux.org/getrandom.2) syscall is necessary,
+since it is the backend for
+[getentropy(3)](https://man.voidlinux.org/getentropy.3), which is the only
+random number backend implemented.
+
+## Disclaimer
+
+This is experimental code and ideas, and shouldn't be put anywhere near any sort
+of production. However, I am open to suggestions and improvements, so feel free
+to reach out.