BearSSL (https://www.bearssl.org) is a TLS(SSL) library written by
Thomas Pornin that is optimized for lower-memory embedded systems
like the ESP8266. It supports a wide variety of modern ciphers and
is unique in that it doesn't perform any memory allocations during
operation (which is the unfortunate bane of the current axTLS).
BearSSL is also absolutely focused on security and by default performs
all its security checks on x.509 certificates during the connection
phase (but if you want to be insecure and dangerous, that's possible
too).
While it does support unidirectional SSL buffers, like axTLS,
as implemented the ESP8266 wrappers only support bidirectional
buffers. These bidirectional buffers avoid deadlocks in protocols
which don't have well separated receive and transmit periods.
This patch adds several classes which allow connecting to TLS servers
using this library in almost the same way as axTLS:
BearSSL::WiFiClientSecure - WiFiClient that supports TLS
BearSSL::WiFiServerSecure - WiFiServer supporting TLS and client certs
It also introduces objects for PEM/DER encoded keys and certificates:
BearSSLX509List - x.509 Certificate (list) for general use
BearSSLPrivateKey - RSA or EC private key
BearSSLPublicKey - RSA or EC public key (i.e. from a public website)
Finally, it adds a Certificate Authority store object which lets
BearSSL access a set of trusted CA certificates on SPIFFS to allow it
to verify the identity of any remote site on the Internet, without
requiring RAM except for the single matching certificate.
CertStoreSPIFFSBearSSL - Certificate store utility
Client certificates are supported for the BearSSL::WiFiClientSecure, and
what's more the BearSSL::WiFiServerSecure can also *require* remote clients
to have a trusted certificate signed by a specific CA (or yourself with
self-signing CAs).
Maximum Fragment Length Negotiation probing and usage are supported, but
be aware that most sites on the Internet don't support it yet. When
available, you can reduce the memory footprint of the SSL client or server
dramatically (i.e. down to 2-8KB vs. the ~22KB required for a full 16K
receive fragment and 512b send fragment). You can also manually set a
smaller fragment size and guarantee at your protocol level all data will
fit within it.
Examples are included to show the usage of these new features.
axTLS has been moved to its own namespace, "axtls". A default "using"
clause allows existing apps to run using axTLS without any changes.
The BearSSL::WiFi{client,server}Secure implements the axTLS
client/server API which lets many end user applications take advantage
of BearSSL with few or no changes.
The BearSSL static library used presently is stored at
https://github.com/earlephilhower/bearssl-esp8266 and can be built
using the standard ESP8266 toolchain.
* Fix WebServerSecure streamFile()
ESP8266WebServerSecure's streamFile was using the base class' method
which did not use SSL encrypt before transmitting, leading to failure.
Add a new template method and required support for
WiFiClientSecure::write(Stream&) (using a local temp buffer since the
SSL libs do not grok Arduino Streams at all).
Fixes#4544
* Match ClientContext buffer and yield() behavior
ClientContext sends out 256 bytes at a time and gives a yield after
each chunk to ensure the WDT doesn't fire. Mimic that behavior in
WiFiClientSecure::write(Stream&).
* Fix leak on multiple SSL server connections
Fixes#4302
The refcnt setup for the WiFiClientSecure's SSLContext and ClientContext
had issues in certain conditions, causing a massive memory leak on each
SSL server connection. Depending on the state of the machine, after two or
three connections it would OOM and crash.
This patch replaces most of the refcnt operations with C++11 shared_ptr
operations, cleaning up the code substantially and removing the leakage.
Also fixes a race condition where ClientContext was free'd before the SSLContext
was stopped/shutdown. When the SSLContext tried to do ssl_free, axtls would
attempt to send out the real SSL disconnect bits over the wire, however by
this time the ClientContext is invalid and it would fault.
* Separate client and server SSL_CTX, support both
Refactor to use a separate client SSL_CTX and server SSL_CTX. This
allows for separate certificates to be installed on each, and means
that you can now have both a *single* client and a *single* server
running in parallel at the same time, as they'll have separate memory
areas.
Tested using mqtt_esp8266 SSL client with a client certificate and a
WebServerSecure with its own custom certificate and key in parallel.
* Add brackets around a couple if-else clauses
Adds SSL server mode for WiFiServerSecure, for plain SSL connections,
ESP8266WebServerSecure, for HTTPS web serving, and SecureHTTPSUpdater for
encrypted OTA updates.
Example code is provided for all new options, as well as a BASH script for
generating their own, self-signed certificates.
Both ESP8266WebServerSecure and SecureHTTPSUpdater are important for secure
password-based authentication. HTTP Basic Authentication, the only supported
model presently, sends the username and password in *cleartext* and therefore
should *never* be used in any un-SSL encrypted channel unless you don't mind
sharing your login and password with anyone else on the internet. Even if the
ESP8266 is not safety critical, this cleartext broadcast could expose you should
you reuse this password elsewhere on your network or the internet.
Mainly useful for testing WiFiClientSecure in local environments.
If allowSelfSignedCerts is called before verifyCertChain, then the
certificate chain will be verified, but the final certificate may be
self-signed.
