Custom capability for a single user

I have this complex scenario:

1) I'll have multiple admin users.

2) Only one admin can 'see_encrypted_pass'

Now, I want to assign custom 'see_encrypted_pass' capability to only one admin (say, John). I have a restricted page containing encrypted password. I want to use this on that page-

if(current_user_can('see_encrypted_pass')){
    //show encrypted password
}

How do I do that?