This is the first that I've heard of ChaCha for encryption (<a href="https://en.wikipedia.org/wiki/Salsa20#ChaCha_variant" rel="nofollow">https://en.wikipedia.org/wiki/Salsa20#ChaCha_variant</a>).<p>Apparently it's a standard that Google is pushing to replace RC4 and already is using for HTTPS between google.com and Android.<p>If arc catches on I'm curious if it could support inline operations. E.g. on a 100gb+ archive can I read the tar index without decrypting the entire archive first, can I extract a single file? The ChaCha algorithm is a <i>streaming cipher</i>, which as I understand suggests that I cannot do operations like that.<p>Even worse now that I'm thinking about this, if my archive has a bit error early in the file does that mean the entire archive cannot be decrypted. Maybe for long term storage I'm better off physically securing my archives than encrypting them to avoid bit rot ruining everything.