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Or does OpenSSL derive the IV by the decryption key somehow from the packet ? Well, yes. Actually, it's not that complicated; for DTLS and AES-CBC mode, the IV is the first 16 bytes of the encrypted region, so it just reads it from there, and starts decrypting from there. In DTLS, we assume that encrypted packets can be dropped in flight (or received ...


The SNI extension is plain text in the ClientHello. This means that it is possible to passively snoop the value and redirect the traffic. This is already used in practice, i.e. haproxy has this feature for several years.


Most likely, the hardware engine has an API accepting an IV of 256 bits (32 bytes) and a data block of some size multiple of 512 bits (64 bytes), and returns a result of 32 bytes. Given that SHA-256 is a Merkle-Damgård hash, in order to chain invocations of that API, you want to pass the SHA-256 IV (given by FIPS 186-4 section 5.3.3) as the IV of the first ...

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