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Padding and record sizes in draft-thomson-http-encryption

From: Peter Beverloo <beverloo@google.com>
Date: Wed, 27 Jan 2016 18:47:21 +0000
Message-ID: <CALt3x6nVoTXLxNCPNjZm9bJ46EKr0OVugLtiFWUVE41epT4oZw@mail.gmail.com>
To: ietf-http-wg@w3.org, Martin Thomson <martin.thomson@gmail.com>
Hi Martin, others,

I have some comments in regards to draft-thomson-http-encryption.

Firstly, each record currently includes between 1 and 256 bytes of padding,
while the default record size is set to 4096 bytes. This is in many cases
not
sufficient, for example in the pad-to-next-power-of-two case.

I've proposed a pull request to change the padding size to two bytes.
  https://github.com/martinthomson/http-encryption/pull/7

The draft defines a streaming model having a sender-configurable record
size.
What is the motivation for allowing this by default? TLS defines 16KB
records
and only allows negotiation of this value per an extension.

Of course, introducing a fixed record size would violate the requirement
set by
draft-ietf-webpush-encryption of only allowing a single record, for any
message
that is larger than said size. A reasonably clean way of addressing this
would
be to separate the Content-Encoding values: aesgcm128 vs.
aes128gcm-streaming.

As a slight meta question, what are the expected users of the streaming
model?

Thanks,
Peter
Received on Wednesday, 27 January 2016 18:47:52 UTC

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