[[https://github.com/kokke/tiny-AES128-C|tiny AES128]] works great as portable C library

  * [[http://stackoverflow.com/questions/9049789/aes-encryption-key-versus-iv|how to use Initialization Vector (IV)]]

AXTLS:

  * [[http://axtls.sourceforge.net/faq.htm|FAQ]]

keys:

  * [[http://smallsrv.com/gsert.cgi|online generation]]

8266:

  * [[http://bbs.espressif.com/viewtopic.php?t=602|example code for TLS]]
  * [[http://bbs.espressif.com/viewtopic.php?f=21&t=389|another example]] (check this one first)

certificates

  * [[http://stackoverflow.com/questions/26873612/what-is-an-ssl-certificate-chain-file|chain file explanation and usage]]
  * [[http://stackoverflow.com/questions/188266/how-are-ssl-certificates-verified|explanation of process]]
  * [[https://blog.talpor.com/2015/07/ssltls-certificates-beginners-tutorial/|another explanation/tutorial]]

===== Getting certificate chain to work for letsencrypt =====

  * [[https://www.identrust.com/certificates/trustid/root-download-x3.html|root cert for letsencrypt needed (in PEM format)]]
  * there's extra spaces at the end of the cert. Take them out.
  * add BEGIN CERTIFICATE and END CERTIFICATE as "described" [[https://www.identrust.com/certificates/trustid/install-nes36.html|here]].
  * confirm the cert is good/readable. Tips on that as well as converting between formats [[https://support.ssl.com/Knowledgebase/Article/View/19/0/der-vs-crt-vs-cer-vs-pem-certificates-and-how-to-convert-them|here]]
  * convert to DER format using same link above
  * use [[https://www.lettercount.com/|this]] to find out how many characters long the DER format cert is
  * convert cert to hex using [[http://tomeko.net/online_tools/file_to_hex.php?lang=en|this]]

==== References ====


  * view cert in [[https://hexed.it/|a hex editor ]]if needed
  * [[https://github.com/esp8266/Arduino/issues/3340|pointers, including identifying the correct root cert to us]]
  * [[https://letsencrypt.org/certificates/|letsencrypt certificates]]
  * [[https://community.letsencrypt.org/t/how-to-get-certificate-of-certification-authority/22029/7|how to get the root cert of a CA]]


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