Misusage of `strlen_p()`

[Jeremaiha-xmetix]

There is no actual reason to put a method that counts characters inside a for-loop, such that every iteration will reevaluate the length of signMessage.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[Jeremaiha-xmetix]

Thank you for your merge @alranel