Problem: Assertion failed: rc == 0 (src/curve_client.cpp:273)

[hintjens]

This happens in the client stack if you specify a null (all zeros) server key, and if you are using libsodium stable. Using older versions of libsodium or tweetnacl, this assert does not happen.

The cause is a change in the API where crypto_box () returns -1 on a null server key, whereas it used to ignore this error (as it ignores other invalid server keys).

Solution: do not assert on this error, handle it gracefully.

[hintjens]

Note that the same logic exists in the server and is probably a DoS vulnerability. I've not tested that but will remove the assert in the corresponding place.