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.