Allow users to hash archive video list for privacy

[ogekve]

• I've verified and I assure that I'm running youtube-dl 2017.02.24.1
• At least skimmed through README and most notably FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones
• Feature request (request for a new functionality)

Some users might wish to not keep a list of every youtube video they have downloaded. I feature that allowed users to keep the URL list hashed instead of in plaintext would allow those users to keep their list a little more private.

The first line of the archive file (which now just starts with a list of URLs that have been downloaded) could have a SALT generated on the first time the feature was used by the user for that archive file. The salt and the URL SHA (or any hash type you think would work) could be hashed together:

1 youtube 00000000000
2 youtube 11111111111

1 f2f442acd3fb68920918936dfb0c9242f1c8149061b1ea58 #the salt that was placed in the first line of the archive file.
2 d8ccc614e4188ba03a37c55e79570266edb782d323945f43df99719c8d501007 #the video that used to be in the first line="youtube 00000000000"
3 87133a643f42616d308d16964325b1093738db8280b7248bf7dbbea94077267a #was "youtube 11111111111"

Example of how to produce the hash using the Salt and normal line:
echo -n "f2f442acd3fb68920918936dfb0c9242f1c8149061b1ea58youtube 00000000000" | openssl sha256
(stdin)= d8ccc614e4188ba03a37c55e79570266edb782d323945f43df99719c8d501007
echo -n "f2f442acd3fb68920918936dfb0c9242f1c8149061b1ea58youtube 11111111111" | openssl sha256
(stdin)= 87133a643f42616d308d16964325b1093738db8280b7248bf7dbbea94077267a

When checking to see if you already have the video downloaded in the hashed archive file you just look up the first line (SALT) and hash it with what you are comparing it against (the current youtube video being downloaded) and then checking the rest of the archive file as normal.

This still allows someone with the salt to determine what you have previously downloaded, but only if they guess the youtube videos ahead of time, comparing each one.

[dstftw]

Keeping your files private is your responsibility not youtube-dl's.