Re: [quicwg/base-drafts] QPACK security considerations (#3575)

Mike Bishop <> Wed, 15 April 2020 18:40 UTC

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Date: Wed, 15 Apr 2020 11:40:45 -0700
From: Mike Bishop <>
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Subject: Re: [quicwg/base-drafts] QPACK security considerations (#3575)
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@MikeBishop commented on this pull request.

> +The amount of memory used by the compressor is limited by the protocol using
+QPACK through the definition of the maximum size of the dynamic table, and the
+maximum number of blocking streams. In HTTP/3, these values are controlled by
+the decoder through the setting parameter QPACK_MAX_TABLE_CAPACITY and
+QPACK_BLOCKED_STREAMS, respectively (see Section
+{{maximum-dynamic-table-capacity}} and {{blocked-streams}}). The limit on the
+size of the dynamic table takes into account both the size of the data stored in
+the dynamic table, plus a small allowance for overhead.  The limit on the number
+of blocked streams is only a proxy for the maximum amount of memory required by
+the decoder.  The actual maximum amount of memory will depend on how much memory
+the decoder uses to track each blocked stream.
+A decoder can limit the amount of state memory used for the dynamic table by
+setting an appropriate value for the maximum size of the dynamic table. In
+HTTP/3, this is realized by setting an appropriate value for the
+QPACK_MAX_TABLE_CAPACITY parameter. An encoder can limit the amount of state

It's an (unstated) norm to omit SETTINGS_ in cases where it's already blatantly obvious that we're discussing a setting.  You'll find similar variance in 7540, 7541, and HTTP/3.

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