Comment 7 for bug 576750

Here's a quick work around while you wait for certificates to be updated etc.

Add to the end of your ~/.subversion/servers file:
  ssl-trust-default-ca = no

more write up here:
http://jamescrisp.org/2010/06/05/workaround-for-subversion-svn-certificate-verification-error-insecure-algorithm-on-ubuntu-1004-lucid-lynx/