The remote Debian host is missing a security-related update.
Daniel J. Bernstein, Joachim Breitner, Daniel Genkin, Leon Groot Bruinderink, Nadia Heninger, Tanja Lange, Christine van Vredendaal and Yuval Yarom discovered that Libgcrypt is prone to a local side-channel attack allowing full key recovery for RSA-1024. See https://eprint.iacr.org/2017/627 for details.
Upgrade the libgcrypt20 packages. For the oldstable distribution (jessie), this problem has been fixed in version 1.6.3-2+deb8u4. For the stable distribution (stretch), this problem has been fixed in version 1.7.6-2+deb9u1.