Spot-On only supports version 1.5.x of gcrypt.

OS X (32-bit)

You may download the GPGTools installer from http://www.gpgtools.org.

OS X (64-bit)

Developers, please download the libgcrypt source from
ftp://ftp.gnupg.org/gcrypt/libgcrypt and the libgpg-error source from
ftp://ftp.gnupg.org/gcrypt/libgpg-error.

Windows

Developers, please download the Gpg4win installer from
http://www.gpg4win.org.
