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I am running Gentoo Hardened with kernel 4.1.7-hardened-r1 and I am trying to encrypt a file using GPG from a shell session opened from SSH and with the DISPLAY variable disabled in order to use pinentry-curses for password prompt. Using gpg -o file.gpg --symmetric file I can encrypt just fine. Using pv file | gpg -o file.gpg --symmetric I get the following error message:
gpg-agent[30745]: command get_passphrase failed: Inappropriate ioctl for device
You should set the GPG_TTY environment variable for it to work, as in this document:
GPG_TTY=$(tty)
export GPG_TTY
Those two lines are supposed to be in your ~/.bashrc (assuming bash), so they're run every time you open new terminal session.
There's another solution, though: in bash you can run your pv and pretend it's a file, using process substitution:
gpg -o file.gpg --symmetric <(pv file)
As such, it might not be a good idea to pipe-in things to programs that expect additional input. It can work differently than expected.
dsfargeg, encrypt it with pv dsfargeg | gpg -o dsfargeg.gpg --symmetric, enter a password when prompted, decrypt the output with gpg -o dsfargeg.gpg.dec --decrypt dsfargeg.gpg, enter your password, and compare the original and the decrypted file with sha256sum dsfargeg dsfargeg.gpg.dec. Both hashes will be the same.
/dev/tty on Debian. This was version 1.4, though, in my case; gpg got a bit of overhaul since. That approach might've been dropped for some reason - you might want to find out more on your own (or this can be some Debian specific patch). As such, it would be probably better for you not to count on it. I'll dig around in traces, to check what's exactly happening in newer gpg (I've got 2.1).