cm/kem/pbkdf2

    PBKDF2 KEM.
    => RFC 2898, PBKDF2

        kem-pbkdf2 {
            {field . {map}}
            {field a {str} =pbkdf2}
            {field cek {bin} >0} {# wrapped CEK}
            {field hash {str} >0} {# hash algorithm identifier}
            {field iter {int} >0} {# number of iterations}
            {field salt {bin} >0}
            {field wrap {str} >0} {# key wrapping algorithm identifier}
        }

    Key wrapping algorithm may be one of:
    [cm/keywrap/xchapoly], [cm/keywrap/kexp15],
    depending on the hash chosen.