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Re: [Linux-ima-devel] [PATCH 0/7] IMA: new parser for ima_restore_measurement_list()

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On 5/16/2017 9:00 PM, Ken Goldman wrote:
> On 5/16/2017 8:53 AM, Roberto Sassu wrote:
>> A new IMA measurement list format, called Crypto Agile, will be introduced
>> shortly to take full advantage of the algorithm flexibility of TPM 2.0.
>> With the new format, it will be possible to provide for each list entry
>> multiple digests, each calculated with an algorithm supported by the TPM.
>> Those digests will be used by remote entities to verify the integrity of
>> the measurements list.
>>
>> The current (SHA1) and the new (Crypto Agile) format definitions are:
>>
>> SHA1: pcr[4] digest[20]
>>        template_name_len[4] template_name[template_name_len]
>>        template_data_len[4] template_data[template_data_len]
>>
>> Crypto Agile: pcr[4] total_digest_len[4]
>>                digest1_len[4] digest1[digest1_len] ...
>>                digestN_len[4] digestN[digestN_len]
>>                template_name_len[4] template_name[template_name_len]
>>                template_data_len[4] template_data[template_data_len]
>
> 1 - In this proposed format, how does the parser or consumer of the log
> know what algorithm is used for digestN.

The format of digestN is: <algo name>:\0<digest value>, the same used
for the file digest.


> For example, the TCG standard format uses TPML_DIGEST_VALUES
> 	uint32_t count - the number of digests TPMT_HA
> 	TPMT_HA digests[]
>
> where a TPMT_HA is
> 	algorithm identifier
> 	digest byte array
>
> 2 - Not a criticism, just a question for understanding ...  Would it be
> true that the total_digest_length == the sum of all the digestN_len
> values plus 4 bytes for each length.

Yes.


> Does it determine how many digests there are by when the total length is
> consumed?

Yes. Since the number of digests is unknown until the buffer is parsed,
the parser consumes the data until the buffer end is reached. Then,
it returns the number of digests to the caller.

Roberto

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[PATCH 0/7] IMA: new parser for ima_restore_measurement_list() Roberto Sassu <roberto.sassu@huawei.com> - 2017-05-16 15:00 +0200
  [PATCH 4/7] ima: declare get_binary_runtime_size() as non-static Roberto Sassu <roberto.sassu@huawei.com> - 2017-05-16 15:00 +0200
  [PATCH 1/7] ima: introduce ima_parse_buf() Roberto Sassu <roberto.sassu@huawei.com> - 2017-05-16 15:00 +0200
  [PATCH 7/7] ima: fix get_binary_runtime_size() Roberto Sassu <roberto.sassu@huawei.com> - 2017-05-16 15:00 +0200
  [PATCH 6/7] ima: add securityfs interface to restore a measurements list Roberto Sassu <roberto.sassu@huawei.com> - 2017-05-16 15:00 +0200
  [PATCH 5/7] ima: add securityfs interface to save a measurements list with kexec header Roberto Sassu <roberto.sassu@huawei.com> - 2017-05-16 15:00 +0200
  Re: [Linux-ima-devel] [PATCH 0/7] IMA: new parser for  ima_restore_measurement_list() Ken Goldman <kgold@linux.vnet.ibm.com> - 2017-05-16 21:10 +0200
    Re: [Linux-ima-devel] [PATCH 0/7] IMA: new parser for  ima_restore_measurement_list() Roberto Sassu <roberto.sassu@huawei.com> - 2017-05-17 09:30 +0200
      Re: [Linux-ima-devel] [PATCH 0/7] IMA: new parser for  ima_restore_measurement_list() Ken Goldman <kgold@linux.vnet.ibm.com> - 2017-05-17 18:30 +0200
        Re: [Linux-ima-devel] [PATCH 0/7] IMA: new parser for  ima_restore_measurement_list() Roberto Sassu <roberto.sassu@huawei.com> - 2017-05-18 11:40 +0200
          Re: [Linux-ima-devel] [PATCH 0/7] IMA: new parser for  ima_restore_measurement_list() Ken Goldman <kgold@linux.vnet.ibm.com> - 2017-05-23 22:50 +0200
            Re: [Linux-ima-devel] [PATCH 0/7] IMA: new parser for  ima_restore_measurement_list() Roberto Sassu <roberto.sassu@huawei.com> - 2017-05-24 10:30 +0200
          Re: [Linux-ima-devel] [PATCH 0/7] IMA: new parser for  ima_restore_measurement_list() Ken Goldman <kgold@linux.vnet.ibm.com> - 2017-05-23 23:20 +0200

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