I grabbed the signapk.jar and keys from here: I Created Auto-Sign app for update.zip and Launcher.apk!
ossibly abandoned! - xda-developers
used the syntax: "java -jar signapk.jar testkey.x509.pem testkey.pk8 oldfilename.zip newfilename.zip"
I've also tried with testsign.jar from here: xda-developers - View Single Post - Signing update.zip in Linux
used the syntax: "java -classpath testsign.jar testsign update.zip update_signed.zip"
I'm running Linux Mint 11 64-bit, and every time I sign the zip file, no errors come up but then when I copy the file over to my SD card and try and flash it, my phone says "signature verification failed, Installation aborted."
It installs fine if I toggle signature verification off...

used the syntax: "java -jar signapk.jar testkey.x509.pem testkey.pk8 oldfilename.zip newfilename.zip"
I've also tried with testsign.jar from here: xda-developers - View Single Post - Signing update.zip in Linux
used the syntax: "java -classpath testsign.jar testsign update.zip update_signed.zip"
I'm running Linux Mint 11 64-bit, and every time I sign the zip file, no errors come up but then when I copy the file over to my SD card and try and flash it, my phone says "signature verification failed, Installation aborted."
It installs fine if I toggle signature verification off...