I'm on Debian and I have a folder, with thousands of files inside it, that has a size of about 14GB. From this folder I have created two encrypted archives: one is a password protected .7z archive, the other is a TAR archive encrypted with ccrypt (.tar.cpt).
(From now on I will assume that .7z/7zip archive means password protected .7z/7zip archive)
I have noticed that opening the 7z archive and inserting the password, lets me see the actual content in about 1-2 seconds, maybe less (there's almost no human perceptible time difference from opening this file and the same .7z file without encryption). However, to be able to see the TAR archive content, the ccdecrypt command on the .tar.cpt file much longer about 5-6 minutes. After that I can open the TAR archive and see the actual content in about 1-2 seconds. This leaves me with some questions:
1. Is a 7zip archive's content encrypted?
The difference in time for decrypting two files of about the same size (the .7z is only about 100MB smaller because the files are already in compressed formats) makes me think that while ccrypt encrypts all the content of the TAR archive, 7zip only encrypts the archive containing the files, like if it was a folder (which vaguely is), making difficult to break through it, but the actual content of the archive remains unencrypted. So being able to see the content only takes few seconds with a .7z archive (the time to decrypt the containing archive/check the password), while seeing the .tar files implies that all the 14GB content is ccdecrypted. Did I make the right assumption? If not, can someone please explain me how these two encryption methods differ and work? This specific 7zip archive hides the filenames before the password is inserted, if that's somehow relevant.
2. Does that means minor security of the 7zip archive?
If the assumption in the first point is correct, does that imply that a password protected 7zip archive is less secure than a "fully encrypted" .tar.cpt archive? I know that using 7zip leaves a lot of traces/temporary files of the hypothetical extracted/decrypted archive, but my question is about the actual security of the encrypted archive itself. Furthermore, I will encrypt/decrypt the archive only on my desktop PC, while the file will be stored on a server, so even if someone will ever take control of the server (and not of my PC of course), he will not be able to find any traces of a decompressed archive, given that the archive is never been decompressed on the server, right?
3. Is there a true UNIX alternative?
Is there a software typical of the UNIX world that makes possible to encrypt a TAR archive in the 7zip way, so that i can protect stuff not-so-security-critical (if a .tar.cpt is actually more secure than a .7z like I've assumed) in a way that makes possible to see the files in 2 seconds instead of 5 minutes? I've nothing against 7zip, it's a great utility, but I'm wondering if the pure UNIX world has something similar to offer (I suppose certainly yes). Furthermore, creating an uncompressed TAR archive takes much less time than creating his 7zipped counterpart, even at minimum compression settings, so being able to apply the "7zip crypting method" to a .tar file would be really convenient.
Other UNIX encrypting software like gpg, mcrypt and the old unsecure crypt all make the same ccrypt type of encryption (I mean that they encrypt all the content, not considering the encryption method), while gzip, bzip2, etc., if I am not wrong, cannot encrypt nothing at all, given the UNIX tradition "Do one thing and do it well".
Initially, the fact that is possible to extract a single file from an encrypted 7zip archive in a bunch of seconds, more or less like with an unencrypted one, was for me another reason to think that the content wasn't actually encrypted, because I didn't know that even a single file can be decrypted from a .7z (and wasn't passed enough time to let me think that the whole archive was decrypted to give me that single file).
Furthermore, I recorded the extraction times of the encrypted and unencrypted versions of the same 7zip archive, and the difference wasn't noticeable at all. I thought that this was another proof of the content being unencrypted, but I was one more time wrong, because I wasn't considering that modern CPUs have encryption bult-ins for popular algorithms like AES (as suggested in the accepted answer).
The 7zip archive can apparently be set to 'no compression' only through command line, or at least not through GUI with Ark (setting the slider to 'minimum' still compresses the archive). Without compression (-mx=0 switch, from the same answer) the .7z size and making time are, more or less, identical to those of the .tar counterpart.
Even not considering the advantage in time of a .7z header over .tar.cpt to show the file list, ccrypt only uses 1 core for encryption/decryption, which makes the process even slower.
I edited the question to make it more readable. Having the accepted answer appropriate quotes, I hope it's still fully understandable.