Use AES128-CBC instead of DES-CBC cipher fro pkcs7 envelopes

[stv0g]

Fixes #16

[CLAassistant]

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[stv0g]

Sorry, but I wont sign a CLA

https://www.linuxjournal.com/content/contributor-agreements-considered-harmful

[hslatman]

That's fair. I can the subject up in our open source triage meetings.