Comment 1 for bug 692536

Citing /usr/share/doc/gnupg/README.BUGS.Debian.gz:

gnupg: Piping content to gpg: echo foo | gpg --use-agent ... errors out with
       `gpg: cancelled by user'

    This might happen when gpg is unable to determine the correct name of the
    terminal. You can check the terminal given to the agent by running
    gpg-agent with the --debug-level advanced switch. The output might contain:

        gpg-agent[XXX] DBG: <- OPTION ttyname=/dev/tty

    whereas the output of tty says

        /dev/pts/X

    You'll have to set GPG_TTY to point to the correct terminal (see also
    gpg-agent(1)).

    Debian #359758 <URL:http://bugs.debian.org/359758>
    GnuPG #1047 <URL:https://bugs.g10code.com/gnupg/issue1047>

Setting your report to invalid. Reopen if the above doesn't fit your problem (but read the linked bug reports - they contain the explanation by the upstream author).