% ./ssldump -d -A -n -k doesnotexistatall -r .my.pcap
New TCP connection #1: 10.71.0.253(50959) <-> 192.0.2.248(443)
1 1 0.2382 (0.2382) C>SV3.0(103) Handshake
ssldump did not complain that the keyfile "doesnotexistatall" is missing (and, of course, it did not decrypt)
ssldump-0.9b3
Apparently, it happens because ssldump was compiled without OpenSSL (which is the case of the Ubuntu package). I suggest to produce an error message ("-k requires a ssldump compiled with OpenSSL") instead of silently ignoring it.