SubjectPublicKeyInfo    ::=     SEQUENCE {
       algorithm       AlgorithmIdentifier,
       subjectPublicKey        BIT STRING
}

##</code><code>##

$asn->prepare(q<
    str BIT STRING
>)
# Method1: length is multiple of 8
$asn->encode(str => "UU");
# Method2: length is explicit
$asn->encode(str => ["UU", 12]);