A classic opportunity for the flip-flop operator.

A bit tricky ... Until you reach BEGIN CERTIFICATE, the if{} is false, so we don't save the lines we read, but @extract is empty, so we continue around the loop. Once we reach the interesting region, we save the lines, and short-circuit the loop to continue reading. After we reach the end, the array has a size, so it is boolean true, and the loop terminates.

open my $file, '<', $filename or die "Could not open $filename $!.\n";
my @extract;
FILE:
while (<$file> ) {
    chomp;
    if ( /BEGIN-CERTIFICATE/ .. /END-CERTIFICATE/ ) {
        push @extraction, $_;
        next FILE;
    }
    last $FILE if @extract;
}
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