At 03:52 AM 11/28/2006, Denis Pinkas wrote:
See my comments embedded.
- ----- Message reçu -----
- De : Russ Housley
- À : Denis Pinkas
- Date : 2006-11-27, 20:03:31
- Sujet : Re: I-D
- >The issue is more complex than presented. :-(
- >The idea is to say that a message is correctly signed by a given
- >signer, if one of the signatures
- >from the *same* signer computed using a different signature
- >algorithm is valid.
- >Correct ?
- You did not acknowledged that this is the goal of the draft proposal.
The document is clear. It says:
... This document
provides replacement text for a few paragraphs, making it
the protected content is valid if any of the digital
signatures for a
particular signer is valid.
- >In the same section from RFC 3852, just above we have:
- >" The process by which signed-data is constructed involves
- > following steps:
- > 1. For each signer, a message digest, or hash value, is
- > on the content with a signer-specific message-digest
- > If the signer is signing any information other than the
- > content, the message digest of the content and the other
- > information are digested with the signer's message digest
- > algorithm (see Section 5.4), and the result becomes the
- > "message digest."
- > 2. For each signer, the message digest is digitally signed
- > the signer's private key.
- > 3. For each signer, the signature value and other
- > information are collected into a SignerInfo value, as
- > in Section 5.3. Certificates and CRLs for each signer, and
- > those not corresponding to any signer, are collected in
- > step.
- > 4. The message digest algorithms for all the signers and
- > SignerInfo values for all the signers are collected
- > with the content into a SignedData value, as defined in
- > 5.1".
- >We should have a similar construct for verification, but we
- When CMS was first adopted by the S/MIME WG, we decided to keep the
- specification as close to the structure of PKCS #7 v1.5 as
- possible. The idea was to make it easy for one to determine the
- differences. I see no reason why this discussion ought to change
- that decision.
- The text from PKCS # 7 v1.5 is:
- A recipient verifies the
signatures by decrypting the encrypted message digest
- for each signer with the signer's public key, then comparing the
- digest to an independently computed message digest. The signer's
public key is
- either contained in a certificate included in the signer information,
or is referenced
- by an issuer distinguished name and an issuer-specific serial number
- identify the certificate for the public key.
- The text from RFC 3852 is:
- A recipient independently computes the message
digest. This message digest and
- the signer's public key are used to verify the signature value.
The signer's public key
- is referenced either by an issuer distinguished name along with an
- serial number or by a subject key identifier that uniquely identifies
- containing the public key. The signer's certificate can be
included in the SignedData
- certificates field.
- These texts are clearly insufficient, since they do not
cover the case of certificate substitution.
- The new draft is wishing to cover the case of signatures
from the same signer.
- It is restricted to the use of certificates. Then the only way to
know that is is the same signer
- is to compare the certificates. We should say some words on how this
comparison shall be done.
- If certificates are substituted, then we are also running into
This is not the issue at all. Different certificates may represent
the same signer in some applications.
- >It should start with:
- > The process by which signed-data is verified involves the
- > following steps:
- > 1. For each SignerInfo present in SignerInfos ...
- >The exercise is more difficult than it looks, because unless
- >ESSCertID is being used,
- >it is not possible to know for sure that a signature is from the
- I recognize that this is true. That is the reason that the proposed
- text points to the application that is using CMS to help when the sid
- field is not sufficient.
- The proposed text is clearly insufficient to cover the
- The second point, which is even more important, is that
I am not convinced
- that this is the right way to solve the problem.
This discussion has been going on for about a year. If you are
unhappy with the proposed solution, do not ask for more work to be done
on it. Instead, propose an alternative. Without such, we
should proceed on the current course.
- If the certificate is used for non repudiation purposes,
then time-stamping provides
- all the necessary protection.
This make no sense to me at all. How does time-stamping facilitate
the transition from RSA with SHA-1 to RSA with SHA-256? In fact, it
make it worse. We need to transition the time stamp authority