If you forget "crypto_key HHHHHHH", a SEGFAULT (or other misbehavior) will result:
clib_memcpy (mp->crypto_key, ck, mp->crypto_key_length);

Multiple instances of this bug in this file. Variables "ck" and "ik" are involved, in both ../vpp-api-test/vat/api_format.c and .../vnet/vnet/ipsec/ipsec_cli.c

This is a good beginner bug for learning how to submit a patch