SQL Server: asymmetric keys

Mapped logins

An asymmetric key can have a login, that is mapped to it:

create login … from asymmetric key …;

An asymmetric key in sys.asymmetric_keys can be joined to the mapped login in sys.server_principals on the sid value:

select
   p.name      login_name,
   p.type_desc           ,  -- ASYMMETRIC_KEY_MAPPED_LOGIN
   a.name      key_name  ,
   a.algorithm_desc      ,
   a.key_length
from
   sys.asymmetric_keys   a                   join
   sys.server_principals p on a.sid = p.sid

If a mapped login exists for an asymmetric key, the asymmetric key cannot be dropped.