SqlCipherHook is an Xposed Framework module that will attempt to capture crypto keys from applications using the SQLCipher library. If it is successful, it will print the keys to the Android log buffers (viewable with logcat). SqlCipherHook is known to work up through version 3.5.7. Feel free to open a ticket if it is not working for your specific version.
You will need to root your test device and install the Xposed Framework. Next, you can:
$ git clone https://github.com/jakev/SqlCipherHook
$ cd SqlCipherHook
$ ./gradlew installDebug
Optionally, you can install the pre-built copy to avoid using Gradle:
$ git clone https://github.com/jakev/SqlCipherHook
$ cd SqlCipherHook
$ adb install ./bin/com.jakev.sqlcipherhook-debug.apk
Once installed, you can interact with your test application while running the following filtered logcat command:
$ adb logcat SqlCipherHook:D *:S
You should see SqlCipher interactions, including the keys used. More information is available in my blog post from 2015.
SqlCipherHook is released under the Apache Software License 2.0.
Thanks to @MDSecLab for doing the research on which methods to hook in the SQLCipher library, and for creating a CydiaSubstrate tweak.