Re: [Cellar] shepherd review of Matroska: part 1

Michael Richardson <> Wed, 06 July 2022 17:59 UTC

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From: Michael Richardson <>
To: Steve Lhomme <>
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Date: Wed, 06 Jul 2022 13:59:03 -0400
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Subject: Re: [Cellar] shepherd review of Matroska: part 1
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Steve Lhomme <> wrote:
    > On 2022-06-12 10:01, Steve Lhomme wrote:
    >>> } ContentEncAlgo Element
    >>> questions will be asked about 1DES, and 3DES.
    >>> 1) We need a note about how legacy files might be encrypted, and we need
    >>>     those definitions for history.

    > AFAIK Matroska files are not encrypted. WebM on the other hand is very
    > common. But we're not making the WebM spec. Content Compression which is
    > parallel to this is however common.

    > In WebM it also depends on the codec what kind of information is actually
    > encrypted. The frame headers are usually not encrypted so they can be parsed
    > without dealing with encryption. Only the actual content part is
    > encrypted.

I think that what we need to explain is that *THIS DOCUMENT* does not define
any encryption scheme.  That is reserves a container/element for schemes that
third parties (WebM) have used, and yes, have an informational reference to

That's all we need to say.

    > defined in Matroska. In the case of WebM, the AES-CTR
    > (AESSettingsCipherMode=1) really tells the whole story of how the
    > encrypted data fill the Block.

Yes, but not how/where the key comes from, which is where we will get into trouble.

Michael Richardson <>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide