Ma proc pour installer les certificats cacert en tant que certificats système (car sinon on se tape un warning à la con / nexus5 android4.4):
wget https://www.cacert.org/certs/root.crt
wget https://www.cacert.org/certs/class3.crt
cat root.crt > 5ed36f99.0
cat class3.crt > e5662767.0
openssl x509 -inform PEM -text -in root.crt -out /dev/null >> 5ed36f99.0
openssl x509 -inform PEM -text -in class3.crt -out /dev/null >> e5662767.0
~/bin/android-sdk-linux/platform-tools/adb push e5662767.0 /sdcard/
~/bin/android-sdk-linux/platform-tools/adb push 5ed36f99.0 /sdcard/
~/bin/android-sdk-linux/platform-tools/adb shell
su
mount -o remount,rw /system
cp /sdcard/5ed36f99.0 /system/etc/security/cacerts/
cp /sdcard/e5662767.0 /system/etc/security/cacerts/
cd /system/etc/security/cacerts/
chmod 644 5ed36f99.0
chmod 644 e5662767.0
reboot