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69 lines
3.7 KiB
Markdown
69 lines
3.7 KiB
Markdown
WiFiClientSecure
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================
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The WiFiClientSecure class implements support for secure connections using TLS (SSL).
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It inherits from WiFiClient and thus implements a superset of that class' interface.
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There are three ways to establish a secure connection using the WiFiClientSecure class:
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using a root certificate authority (CA) cert, using a root CA cert plus a client cert and key,
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and using a pre-shared key (PSK).
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Using a root certificate authority cert
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---------------------------------------
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This method authenticates the server and negotiates an encrypted connection.
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It is the same functionality as implemented in your web browser when you connect to HTTPS sites.
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If you are accessing your own server:
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- Generate a root certificate for your own certificate authority
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- Generate a cert & private key using your root certificate ("self-signed cert") for your server
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If you are accessing a public server:
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- Obtain the cert of the public CA that signed that server's cert
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Then:
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- In WiFiClientSecure use setCACert (or the appropriate connect method) to set the root cert of your
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CA or of the public CA
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- When WiFiClientSecure connects to the target server it uses the CA cert to verify the certificate
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presented by the server, and then negotiates encryption for the connection
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Please see the WiFiClientSecure example.
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Using a root CA cert and client cert/keys
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-----------------------------------------
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This method authenticates the server and additionally also authenticates
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the client to the server, then negotiates an encrypted connection.
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- Follow steps above
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- Using your root CA generate cert/key for your client
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- Register the keys with the server you will be accessing so the server can authenticate your client
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- In WiFiClientSecure use setCACert (or the appropriate connect method) to set the root cert of your
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CA or of the public CA, this is used to authenticate the server
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- In WiFiClientSecure use setCertificate, and setPrivateKey (or the appropriate connect method) to
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set your client's cert & key, this will be used to authenticate your client to the server
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- When WiFiClientSecure connects to the target server it uses the CA cert to verify the certificate
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presented by the server, it will use the cert/key to authenticate your client to the server, and
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it will then negotiate encryption for the connection
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Using Pre-Shared Keys (PSK)
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---------------------------
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TLS supports authentication and encryption using a pre-shared key (i.e. a key that both client and
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server know) as an alternative to the public key cryptography commonly used on the web for HTTPS.
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PSK is starting to be used for MQTT, e.g. in mosquitto, to simplify the set-up and avoid having to
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go through the whole CA, cert, and private key process.
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A pre-shared key is a binary string of up to 32 bytes and is commonly represented in hex form. In
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addition to the key, clients can also present an id and typically the server allows a different key
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to be associated with each client id. In effect this is very similar to username and password pairs,
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except that unlike a password the key is not directly transmitted to the server, thus a connection to a
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malicious server does not divulge the password. Plus the server is also authenticated to the client.
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To use PSK:
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- Generate a random hex string (generating an MD5 or SHA for some file is one way to do this)
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- Come up with a string id for your client and configure your server to accept the id/key pair
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- In WiFiClientSecure use setPreSharedKey (or the appropriate connect method) to
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set the id/key combo
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- When WiFiClientSecure connects to the target server it uses the id/key combo to authenticate the
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server (it must prove that it has the key too), authenticate the client and then negotiate
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encryption for the connection
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Please see the WiFiClientPSK example.
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