I wrote a program before for reads simulation of NGS, including Solexa/Illumina FASTQ format, SOLiD/ABi color space format, 454/Roche fna/qual format, and it supports Paired-ends, Mate Pairs, or reads with adapter/primers/cloning vector, and enzyme digestion site, etc. and it will generate diversity/mutation including SNPs, Indels, SVs. But it still not released yet. But refer to your question, I don't think you need to focus on simulating quality scores for your simulated Illumina reads. However, I think the random quality is OK, but actually, the right most 5~20bp of the 3' of the reads will be lower, so you can follow this subroutine(PERL),
#Usage: generate_qual(\$quality, $Reads_length);
sub generate_qual
{
my ($Reads_length,$quality) = @_;
for (my $i=0;$i<$Reads_length-5;$i++)
{
$$quality .= chr(int(rand(36))+74);
}
for (my $i=$Reads_length-5;$i<$Reads_length;$i++)
{
$quality .= chr(int(rand(46))+64);
}
}
Here, $Reads_length=100 as your requirement.
The simNGS package can simulate paired-end library construction (with adjustable mean and std dev) and sample preparation errors (substitutions and indels) as well. The sample prep error rate is properly incorporated in the simulated quality scores.