# Signing the Android build

Every build produces an APK. Which key signs it depends entirely on whether
four secrets are present:

| secret | what it is |
|---|---|
| `ANDROID_KEYSTORE_BASE64` | the keystore file, base64-encoded |
| `ANDROID_KEYSTORE_PASSWORD` | the store password |
| `ANDROID_KEY_ALIAS` | the alias of the key inside the store |
| `ANDROID_KEY_PASSWORD` | the key password |

With none of them set, `docker/android/assemble-apk.sh` generates a throwaway
debug key and signs with that. That is the right answer for a branch build or
a fork: the APK installs on a test device and nothing pretends it is a
release. With all of them set, the same script signs with the real key.

The names match JellyTau's deliberately. One convention across both Android
projects is one thing to remember instead of two.

## Making the key

Once, and then never again — keep it forever. Android identifies an app by
its signature, so an app signed with a new key is a *different* app to every
device that has the old one installed. There is no recovery from losing it
beyond telling everybody to uninstall and reinstall.

    keytool -genkeypair -v \
        -keystore darkroom-release.jks \
        -alias darkroom \
        -keyalg RSA -keysize 4096 -validity 10000 \
        -dname "CN=Duncan Tourolle, O=tourolle.paris, C=FR"

`keytool` prompts for the passwords rather than taking them on the command
line, which keeps them out of shell history. Back the `.jks` up somewhere that
is not this repository and not the machine that builds it.

## Loading the secrets

    base64 -w0 darkroom-release.jks > /tmp/ks.b64
    tea api --method PUT /repos/dtourolle/DarkRoom/actions/secrets/ANDROID_KEYSTORE_BASE64 \
        -f data=@/tmp/ks.b64
    shred -u /tmp/ks.b64

    # and the three strings, read rather than typed so they miss the history
    read -rs PW && tea api --method PUT \
        /repos/dtourolle/DarkRoom/actions/secrets/ANDROID_KEYSTORE_PASSWORD -f data="$PW"

...and the same for `ANDROID_KEY_PASSWORD` and `ANDROID_KEY_ALIAS`. Or paste
them into Settings → Actions → Secrets in the web UI, which is less fiddly and
just as good.

## Checking which key signed a build

The packaging step prints it, and the APK carries it:

    apksigner verify --print-certs darkroom.apk

A debug build says `CN=Android Debug`. Anything else is the real key.

## Signing locally

`docker/android/package.sh` takes the same environment variables, so a local
release-signed build is:

    KEYSTORE=$PWD/darkroom-release.jks KEY_ALIAS=darkroom \
    KEYSTORE_PASS=... KEY_PASS=... ./docker/android/package.sh

Without them it debug-signs, and keeps one debug keystore in the build cache
so repeat installs to a device do not need an uninstall first.