sha1 and rmd160

[Craig Treleaven]

At 11:54 PM -0500 4/5/12, Ryan Schmidt wrote:
>On Apr 5, 2012, at 23:53, Arno Hautala wrote:
>
>>  The preferred hashes are
>>  rmd160 and sha256.
>
>Right. The simplest way to generate them is to remove the checksum 
>lines from the Portfile (or insert invalid rmd160 and sha256 
>checksums into the Portfile), then run "sudo port -d checksum"; 
>MacPorts will print the correct checksum lines that you can copy 
>into the Portfile.
>

Just curious, why two checkums?  Is one not sufficient?

Craig