I would use 7z, There is a download link for it on bleepingcomputer's downloads section, but it would need the other person to run 7z as well. Fortunately 7z is a pretty common program, sometimes it even comes bundled on computers which are new, but it isn't a standard built in function of most operating systems (windows cannot deal with 7z files itself, some linux types might be able to) so for those who haven't installed 7z themselves for some reason in the past they would need to install it before they could opne the encrypted files. One good thing is that being available on this site there is a safe download link you can provide to those people who don't have 7z already. 7z, atleast the version I use (same version as is available at http://www.bleepingcomputer.com/download/7-zip-for-windows/
), can also make self-extracting archives. But there are issues with these. Self-extracting archives are exe files, and if a user is cautious about installing 7z you can be sure they won't feel safe in running an exe file you just sent them.
7z won't free you of the compressing/extracting requirement, it is just like zip files for this, but a bit faster. 7z does however offer more powerful encryption (the type used as standard on zip files is apparently not that strong, whereas 7z uses AES 256) and will allow anyone to encrypt and decrypt files. On the latest versions of windows the built-in zip file processing systems let anyone open zip files if they have the password, but only users of particular (pro and enterprise I think) windows versions can make encrypted archives. With 7z anyone with it installed can make encrypted archives, anyone with 7z installed can open them with the password.
7z archives (especially if you first put the secret files into an ordinary zip file, then put this zip file into an encrypted 7z archive) also give greater protection to information such as the file names, there is an option during encryption to encrypt these so they cannot be seen without entering the password. If you put the secret files in a zip file and then the zip file into a 7z then eavesdroppers couldn't see the individual file sizes either (they might be able to see that the 7z archive held a zip file called secret-files.zip which was a particular number of megabytes in size, but they wouldn't know whether the zip file had one big file, many little ones or a mixture, and they wouldn't know the names of the files within it).
As far as I am aware the only ways of encrypting files without putting them into archives are:
1 )special file formats that only open with specialised programs, the receiver would need the special program installed and you might onyl be able to pass text through rather than files such as images, audio, pdf, video, word documents.
2 )disk encryption and file vaults, things like truecrypt and bitlocker, these sort of things are not usually easily copied from place to place as they are closely connected with the drive on whcih the encrypted files are saved.
3 )manual encryption of file contents, basically encoding your message by hand then typing the ciphertext into a document, very slow and cumbersome to encrypt and de-crypt, not very secure compared to the sorts of ciphers used in other methods.
For encrypted archives RolandJS's concern will not apply, they maintain there encryption wherever they are copied and sent to, the encryption is part of the file, it doesn't get messed up by copying. For types 1 ) and 2 ) discussed above, his concerns can and often will apply. They also likely apply to types of encryption software sometimes bundled on USB sticks when you buy them. His concerns also likely apply for some types of encrypting done by built in tools into windows, older versions atleast. They should not apply to encryption of zip files by window's internal tools, they certainly don't apply to encrytion by 7z.
P.S. How are you telling the recipient the password they need to open the file? Have you pre-agreed it, phoned them to tell them, agreed a common source like "the first 3 words on the second page of a particular newspaper we both read, all written backwards"?
Edited by rp88, 08 May 2015 - 02:07 PM.
Back on this site, for a while anyway, been so busy the last year.
My systems:2 laptops, intel i3 processors, windows 8.1 installed on the hard-drive and linux mint 17.3 MATE installed to USB