Comes down to something I'd like to see support for in perl: unpack on streams. So you could rewrite

while (read $fh, my $dta, 4) {
    my ($name, $len) = unpack "vv", $dta;
    read $fh, $dta, $len;
    $encrypted and $dta = decrypt $dta;
    :
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to

while (my ($name, $dta) = unpack "vv/A*", $fh) {
    $encrypted and $dta = decrypt $dta;
    :
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