opengpg: failure opening keyring '${HOME}/.gnupg/aptlytest.gpg': open ${HOME}/.gnupg/aptlytest.gpg: no such file or directory
Looks like your keyring with trusted keys is empty. You might consider importing some keys.
Downloading http://mirror.yandex.ru/debian-backports/dists/squeeze-backports/InRelease...
openpgp: Signature made Sun, 13 Mar 2016 12:02:54 MSK using RSA key ID 8B48AD6246925553
openpgp: Can't check signature: public key not found
Downloading http://mirror.yandex.ru/debian-backports/dists/squeeze-backports/Release...
Downloading http://mirror.yandex.ru/debian-backports/dists/squeeze-backports/Release.gpg...
openpgp: Signature made Sun, 13 Mar 2016 12:02:54 MSK using RSA key ID 8B48AD6246925553
openpgp: Can't check signature: public key not found
ERROR: unable to fetch mirror: failed to verify detached signature: openpgp: signature made by unknown entity