To make it easier to limit my media consumption, I'd like to temporarily revoke my access to certain digital media files. One solution would be to leave a copy with a friend, and delete my own copy until I'm able to meet the friend to get it back. A solution I'd prefer is to encrypt it with a cypher which takes half an hour or so to decrypt, but I would need to write that algorithm myself unless someone knows of an off the shelf solution.*
What is not an option: installing software to limit the computer's actions. Because it would not properly install or run on my computer, and because I would not run untrusted software with administrative permissions.
*My possible solution based on encryption: a key will be chosen and written to disk. Each block of the file will be encrypted separately, using an "almost key". The "almost key" is the key file, with the last N bits of the file altered. When the block is decrypted, the system will need to guess the last bits. Decryption will be retried until it succeeds. The more bits are changed, the more retries will be needed. Thus smaller files would have more bits changed, so decryption time could be kept constant per file. For example, if the key is
0000, that decryption will be tried first with that key, then with
0011, etc. Each block will use a different "almost key", so the guessing process will need to be redone. Average tries * number of blocks will be constant, for a constant decryption time.