Crackmes.de does not exists anymore. Reversers need to find a place to upload their creation and help new people to learn from that great discipline. This place has been made in order to help you to improve your reversing skills. You can download some crackmes and submit solutions to them.
Obviously, all crackmes available on this website have been made to be cracked.
The password for the files is "crackmes.one". If it does not work, this is probably because the crackme has been imported from crackmes.de, so use the password "crackmes.de" instead.
Every crackme/solution is validated before appearing on the website. This may take anywhere from a few hours to a couple of days
Indeed, but in most cases there's a README/instructions file within the archive.
First, you must login/register. Then, you can upload your solution on the crackme page. Text, markdown, HTML, and similar formats are preferred, but if you think that a video will be clearer, feel free to upload it!
All crackmes available on this site can be used for non-commercial purposes. But please mention the author. :)
This is probably because your solution got rejected. Generally there's only one rule, don't patch! Unless the author explicitely said that patching is a valid solution, don't do it. Write a keygen, find the password. You'll learn more by doing this.