Re: Using Signature Policy in RFC-5126

Yasir,

this specific point has caused many interoperability issues. Not only is 
the concatenation method subject to interpretation, but also, if you 
have several archive timestamps, you have to use heuristics to guess the 
previous encoding of the attribute sequence because it can be in BER.

I can give you my humble interpretation of the way to concatenate but I 
cannot promise it will be the same as everyone else.

There are currently discussions regarding a change of this attribute, 
possibly mandating DER encoding to remove all ambiguities. Do you 
believe such a change would be worthwhile ?

Regards,

--
Julien Stern

Yasir Khan wrote:
> RFC 5126 explains how to create archived time stamp i.e.
> 
>  
> 
>  
> 
> ArchiveTimeStampToken ::= TimeStampToken
> 
>  
> 
>    The value of the messageImprint field within TimeStampToken shall be
> 
>    a hash of the concatenation of:
> 
>  
> 
>       - the encapContentInfo element of the SignedData sequence;
> 
>  
> 
>       - any external content being protected by the signature, if the
> 
>         eContent element of the encapContentInfo is omitted;
> 
>  
> 
>       - the Certificates and crls elements of the SignedData sequence,
> 
>         when present, and;
> 
>  
> 
>       - all data elements in the SignerInfo sequence including all
> 
>         signed and unsigned attributes.
> 
>  
> 
>  
> 
> The ArchiveTimeStamp will be added as an unsigned attribute in the 
> SignerInfo sequence.
> 
>  
> 
> According to the RFC, it is clear that message imprint will be the hash 
> of above concatenated values but it is not explained how to concatenate 
> these values? Please clarify this point. Some hint for implementing this 
> would be highly appreciated. Thanks!
> 
>  
> 
> ----------------------------------------------------------------------------------
> 
> **YASIR KHAN***
> *Development Manager****
> 
>  
> 
> **Ascertia Limited**
> www.ascertia.com <http://www.ascertia.com/>  
> 
> www.globaltrustfinder.com <http://www.globaltrustfinder.com/>
> 
> ----------------------------------------------------------------------------------
> 
> //Delivering Trust for e-business Documents & Workflows//
> 
> ----------------------------------------------------------------------------------
> 
> NOTICE: This message is intended for the recipient(s) only. This 
> communication may contain privileged or other
> 
> confidential information. If you are not the intended recipient, or 
> believe that you have received this communication in
> 
> error, please do not print, copy, retransmit, disseminate, or otherwise 
> use the information. Please notify the sender that
> 
> you have received this email in error, and delete the copy you received
> 
>  
> 
> ------------------------------------------------------------------------
> 
> *From:* owner-ietf-smime <at> mail.imc.org 
> [mailto:owner-ietf-smime <at> mail.imc.org] *On Behalf Of *Pavel V. Smirnov
> *Sent:* Thursday, June 26, 2008 1:04 PM
> *To:* 'Yasir Khan'; ietf-smime <at> imc.org
> *Subject:* RE: Using Signature Policy in RFC-5126
> 
>  
> 
> Yes, I mean “digital signature policy” as a “policy document” present at 
> SPUri. But I use SPUri only for example, you may specify a SigPolicyId 
> and omit sigPolicyQualifiers at all. In this case you have to rely on 
> some other means to convey a correspondence between SigPolicyIds and 
> “policy documents”.
> 
>  
> 
> In case of SPuri you have to retrieve a “policy document” by its URI and 
> hash it.
> 
>  
> 
> Note that if your infrastructure provides a trusted source of “policy 
> documents”, and there will never be two different (versions of) “policy 
> documents” identified by the same OID, you don’t have to hash them at 
> all. Just use zero policy hash value.
> 
>  
> 
> Pavel Smirnov
> 
> Crypto-Pro
> Tel./Fax: +7 495 780-4820
> WWW: http://www.CryptoPro.ru <http://www.cryptopro.ru/>
> e-mail: spv <at> CryptoPro.ru <mailto:spv <at> CryptoPro.ru>
> 
>  
> 
> *From:* owner-ietf-smime <at> mail.imc.org 
> [mailto:owner-ietf-smime <at> mail.imc.org] *On Behalf Of *Yasir Khan
> *Sent:* Thursday, June 26, 2008 12:19 PM
> *To:* Смирнов Павел Владимирович; ietf-smime <at> imc.org
> *Subject:* RE: Using Signature Policy in RFC-5126
> 
>  
> 
> You wrote: ”You have to hash a *digital signature policy* represented as 
> a sequence of bytes in some format and place the computed value in 
> SigPolicyHash.”
> 
>  
> 
> To which item you are naming as “digital signature policy”. You mean 
> policy document present at SPUri? If Yes then it makes some sense. But 
> if only SPUserNotice is present or nothing is present as 
> *sigPolicyQualifiers* as it is an OPTIONAL element:
> 
>  
> 
>             sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF 
> SigPolicyQualifierInfo OPTIONAL
> 
>  
> 
> then on which item the hash would be computed?
> 
>  
> 
> Regards,
> 
> Yasir Khan
> 
>  
> 
>  
> 
> ------------------------------------------------------------------------
> 
> *From:* Pavel V. Smirnov [mailto:spv <at> cryptopro.ru]
> *Sent:* Wednesday, June 25, 2008 4:07 PM
> *To:* 'Yasir Khan'; ietf-smime <at> imc.org
> *Subject:* RE: Using Signature Policy in RFC-5126
> 
>  
> 
> Hello Yasir,
> 
>  
> 
> There is no need to protect by SigPolicyHash other fields of 
> SignaturePolicyId structure because it is placed in a signed attribute. 
> All signed attributes are protected by the signature itself.
> 
>  
> 
> In most cases the policy would be an external document not included in 
> your signed message, and you have to unambiguously indicate specific 
> policy with respect to which your document should be treated. E.g., you 
> may only have an URI pointing to the policy as a SigPolicyQualifier.
> 
>  
> 
> You have to hash a digital signature policy represented as a sequence of 
> bytes in some format and place the computed value in SigPolicyHash.
> 
>  
> 
> Pavel Smirnov
> 
> Crypto-Pro
> Tel./Fax: +7 495 780-4820
> WWW: http://www.CryptoPro.ru <http://www.cryptopro.ru/>
> e-mail: spv <at> CryptoPro.ru <mailto:spv <at> CryptoPro.ru>
> 
>  
> 
> *From:* owner-ietf-smime <at> mail.imc.org 
> [mailto:owner-ietf-smime <at> mail.imc.org] *On Behalf Of *Yasir Khan
> *Sent:* Wednesday, June 25, 2008 2:43 PM
> *To:* ietf-smime <at> imc.org
> *Subject:* Using Signature Policy in RFC-5126
> 
>  
> 
> We have a question related to using the signature policy in the CAdES 
> signatures (EPES) defined in RFC-5126. Here is the relevant structure:
> 
>  
> 
> SignaturePolicyId ::= SEQUENCE {
> 
>             sigPolicyIdentifier SigPolicyId,
> 
>             *sigPolicyHash SigPolicyHash,*
> 
>             sigPolicyQualifiers SEQUENCE SIZE (1..MAX) OF
> 
>             SigPolicyQualifierInfo OPTIONAL
> 
> }
> 
>  
> 
> SigPolicyId ::= OBJECT IDENTIFIER
> 
>  
> 
> *SigPolicyHash ::= OtherHashAlgAndValue*
> 
> * *
> 
> *OtherHashAlgAndValue ::= SEQUENCE {*
> 
> *            hashAlgorithm   AlgorithmIdentifier,*
> 
> *        hashValue       OtherHashValue *
> 
> *}*
> 
>  
> 
> SigPolicyQualifierInfo ::= SEQUENCE {
> 
>             sigPolicyQualifierId SigPolicyQualifierId,
> 
>             sigQualifier ANY DEFINED BY sigPolicyQualifierId
> 
> }
> 
>  
> 
> SigPolicyQualifierId ::= OBJECT IDENTIFIER
> 
> id-spq-ets-uri OBJECT IDENTIFIER ::= {
> 
>             iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) 
> pkcs9(9) smime(16) id-spq(5) 1
> 
> }
> 
> SPuri ::= IA5String
> 
>  
> 
> id-spq-ets-unotice OBJECT IDENTIFIER ::= {
> 
>             iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) 
> pkcs9(9) smime(16) id-spq(5) 2
> 
> }
> 
> SPUserNotice ::= SEQUENCE {
> 
>             noticeRef NoticeReference OPTIONAL,
> 
>             explicitText DisplayText OPTIONAL
> 
> }
> 
>  
> 
> NoticeReference ::= SEQUENCE {
> 
>             organization DisplayText,
> 
>             noticeNumbers SEQUENCE OF INTEGER
> 
> }
> 
>  
> 
> DisplayText ::= CHOICE {
> 
>             visibleString VisibleString (SIZE (1..200)),
> 
>             bmpString BMPString (SIZE (1..200)),
> 
>             utf8String UTF8String (SIZE (1..200))
> 
> }
> 
>  
> 
> In the given structure for CAdES-EPES signature, its is not clear that 
> whether are we computing the hash "SigPolicyHash" over the document at 
> "SPuri" and/or over the "SPUserNotice"
> 
>  
> 
> Are the following combinations valid?
> 
>  
> 
> 1) Only compute hash over document present at SPURI if only SPUri is set
> 
> 2) Only compute hash over SPUserNotice  if only SPUserNotice is set
> 
> 3) Compute hash over document at SPURI and SPUserNotice if both are set
> 
>  
> 
> Please clarify it. Thanks!
> 
>  
> 
> Regards,
> 
>  
> 
> Yasir Khan
> Development Manager
> 
>  
> 
> Ascertia Ltd
> 40 Occam Road
> Surrey Research Park
> Guildford
> Surrey, GU2 7YG
> United Kingdom
> 
>  
> 
> t.  +44 (0)1483 685500
> f.  +44 (0)1483 573704
> 
>  
> 
> www.ascertia.com <http://www.ascertia.com/>   
> 
>  
> 
> -----------------------------------------------------------------
>          Identity Proven, Trust Delivered
> -----------------------------------------------------------------
> 
>  
> 
>  
>