The remote Debian host is missing a security-related update.
Daniel Genkin, Lev Pachmanov, Itamar Pipman and Eran Tromer discovered that the ECDH secret decryption keys in applications using the libgcrypt20 library could be leaked via a side-channel attack. See https://www.cs.tau.ac.IL/~tromer/ecdh/ for details.
Upgrade the libgcrypt20 packages. For the stable distribution (jessie), this problem has been fixed in version 1.6.3-2+deb8u1.