failed to install git-svn

[frankwang@apollo-2 ~]$ sudo port install git-core +svn
Password:
--->  Computing dependencies for git-core
--->  Dependencies to be installed: p5-svn-simple subversion-perlbindings serf0 subversion p5-term-readkey python27 bzip2 gdbm python_select rsync popt
--->  Fetching archive for serf0
--->  Attempting to fetch serf0-0.7.2_0.darwin_10.x86_64.tbz2 from http://packages.macports.org/serf0
--->  Attempting to fetch serf0-0.7.2_0.darwin_10.x86_64.tbz2.rmd160 from http://packages.macports.org/serf0
Error: Target org.macports.archivefetch returned: Failed to verify signature for archive!
Error: Failed to install serf0
Log for serf0 is at: /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_ports_www_serf0/serf0/main.log
Error: The following dependencies were not installed: p5-svn-simple subversion-perlbindings serf0 subversion p5-term-readkey python27 bzip2 gdbm python_select rsync popt
Error: Status 1 encountered during processing.
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