Hello there. FYI, the latest release (0.12) has the dependencies lowered down to the ones which can be found in stable (+ the two missing packages as in sid), effectively making it backportable to stable with little effort (together with libcrypt-rsa-parse-perl and libcrypt-format-perl).
https://github.com/sludin/Protocol-ACME/issues/30 (closed) Best wishes -- Marco
