Messages in this thread | | | Subject | Re: [PATCH 0/2] public key: IMA signer logging: Log public key of IMA Signature signer in IMA log | From | Ken Goldman <> | Date | Wed, 22 May 2019 14:57:28 -0400 |
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On 5/20/2019 7:15 PM, Lakshmi wrote: > On 5/17/19 7:41 AM, Ken Goldman wrote: > > Hi Ken, > > Apologize for the delay in responding. > >> Since a platform typically uses only a few signing keys, 4 bytes makes >> the chance of a collision quite small. The collision would have to be >> within the same log, not global. >> >> In that worst case, the verifier would have to try two keys. It's a >> slight performance penalty, but does anything break? > > Problem Statement: > - If the attestation service has to re-validate the signature reported > in the IMA log, the service has to maintain the hash\signature of all > the binaries deployed on all the client nodes. This approach will not > scale for large cloud deployments.
1 - How is your solution - including a public key with each event - related to this issue?
2 - I don't understand how a large cloud affects scale. Wouldn't the verifier would typically be checking known machines - those of their enterprise - not every machine on the cloud?
Can't we assume a typical attestation use case has a fairly locked down OS with a limited number of applications.
> - Possibility of collision of "Key Ids" is non-zero > - In the service if the "Key Id" alone is used to verify using a map of > "Key Id" to "Signing Key(s)", the service cannot determine if the > trusted signing key was indeed used by the client for signature > validation (Due to "Key Id" collision issue or malicious signature).
Like I said, it should be rare. In the worst case, can't the service tell by trying both keys?
> > Proposed Solution: > - The service receives known\trusted signing key(s) from a trusted > source (that is different from the client machines) > - The clients measure the keys in key rings such as IMA, Platform, > BuiltIn Trusted, etc. as early as possible in the boot sequence. > - Leave all IMA measurements the same - i.e., we don't log public keys > in the IMA log for each file, but just use what is currently available > in IMA.
I thought your solution was to change the IMA measurements, adding the public key to each entry with a new template? Did I misunderstand, or do you have a new proposal?
> > Impact: > - The service can verify that the keyrings have only known\trusted keys.
If the service already has trusted keys from a trusted source, why do they have to come from the client at all?
> - The service can cross check the "key id" with the key rings measured. > - The look up of keys using the key id would be simpler and faster on > the service side. > - It can also handle collision of Key Ids.
How does this solve the collision issue? If there are two keys with the same key ID, isn't there still a collision?
> > Note that the following is a key assumption: > > - Only keys signed by a key in the "BuiltIn Trusted Keyring" can be > added to IMA\Platform keyrings.
I understand how the client keyring is used in IMA to check file signatures, but how is that related to the attestation service?
> > > Thanks, > -lakshmi >
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