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

[Ken Goldman]

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.
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.

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