I suspect you will do no worse letting Perl handle the buffering for you: 
$/ = \8; # Read 8-byte records. Behind the scenes, Perl will do buffer
+ing of reads.
$out_buffer .= blowfishify($_) while <INFILE>;
print OUTFILE $out_buffer;

[download]
Alternatively, you could (with a sufficiently modern Perl) read from your buffer as if it were a filehandle, using the same $/ = \8 trick. 
open BUF, '<', \$buffer or die "$!: Could not open buffer\n";
$/ = \8;
$out_buffer .= blowfishify($_) while <INFILE>;
print OUTFILE $out_buffer;

[download]
They're tidier ways of doing what you want, but you'd have to try them to see whether they buy or lose you any efficiency. My guess is that the I/O isn't going to be the bottleneck, anyway; the encryption is.
Caution: Contents may have been coded under pressure.

In reply to Re^3: Fast parsing for cypher block chaining by Roy Johnson
in thread Fast parsing for cypher block chaining by fluffyvoidwarrior

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