Re: [kitten] Input on Paul's concerns about aes-cbc

Luke Howard <lukeh@padl.com> Wed, 09 October 2013 02:39 UTC

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From: Luke Howard <lukeh@padl.com>
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Date: Wed, 09 Oct 2013 13:38:51 +1100
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References: <tslob752llm.fsf@mit.edu> <524ECE01.3060401@mit.edu> <CAK3OfOger4OxBoBc=jCVBRZeXO2OeJa5mRoONij98gnRFPGMyw@mail.gmail.com> <064ca7780d4943b1868670461c2c7184@BLUPR03MB279.namprd03.prod.outlook.com>
To: Paul Miller <paumil@microsoft.com>
Cc: "kitten@ietf.org" <kitten@ietf.org>, Sam Hartman <hartmans-ietf@mit.edu>
Subject: Re: [kitten] Input on Paul's concerns about aes-cbc
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On 08/10/2013, at 11:22 AM, Paul Miller (NT) <paumil@microsoft.com> wrote:

> With the existing calling pattern used for DES in Windows, callers that did not pass in the SECBUFFER_PADDING into the EncryptMessage call would just fail when the buffer was not aligned.  Additionally, if the buffer was a multiple of the block size then it would not get the PKCS#7 padding and then would fail on the other end that expected the pad block.  I suspect this would break a whole lot of callers.

Are you saying that even for RC4 (where there is one byte of PKCS#7 padding per RFC 4757 7.3), padding would be omitted entirely if the buffer was a multiple of the block size? Isn't this a bug? I noticed this was the case when building an interoperable DCE RPC implementation, but I assumed it was special-cased for GSS_C_DCE_STYLE. [1]

-- Luke

[1] https://github.com/krb5/krb5/blob/master/src/lib/gssapi/krb5/k5sealiov.c#L89

[kitten] Input on Paul's concerns about aes-cbc Sam Hartman
Re: [kitten] Input on Paul's concerns about aes-c… Greg Hudson
Re: [kitten] Input on Paul's concerns about aes-c… Nico Williams
Re: [kitten] Input on Paul's concerns about aes-c… Paul Miller (NT)
Re: [kitten] Input on Paul's concerns about aes-c… Nico Williams
Re: [kitten] Input on Paul's concerns about aes-c… Luke Howard
Re: [kitten] Input on Paul's concerns about aes-c… Martin Rex
Re: [kitten] Input on Paul's concerns about aes-c… Luke Howard
[kitten] DES enctypes are not PKCS#7 padded (Re: … Tom Yu
Re: [kitten] DES enctypes are not PKCS#7 padded (… Luke Howard
Re: [kitten] DES enctypes are not PKCS#7 padded (… Tom Yu
Re: [kitten] Input on Paul's concerns about aes-c… Luke Howard
Re: [kitten] Input on Paul's concerns about aes-c… Tom Yu
Re: [kitten] Input on Paul's concerns about aes-c… Benjamin Kaduk