There are a couple of notes regarding archive timestamp that could help you.
Note 4 says: "The hash is calculated over the concatenated data elements as
received/stored, including the Type and Length encoding".
Julien mentioned a point considered in Note 3: "Unless DER is used
throughout, it is recommended that the binary encoding of the ASN.1
structures being time-stamped be preserved when being archived to ensure
that the recalculation of the data hash is consistent".
So. To simplify your implementation you should use DER encoding everywhere
or just always keep original binary encoding. After that you have to
concatenate binary representations of all the fields listed not trying to
throw away Type and Length tags, or getting all certificates or crls from
Certificates or crls elements of SignedData and concatenating them. Just
concatenate full binary encodings of the listed elements in the mentioned
order. But you have to turn over a SignerInfo sequence: you should not
include outer SignerInfo Type and Length tags in hashing, but rather include
every element of SignerInfo starting from version and finising with
unsignedAttrs.
Said above is enough to add an archive timestamp attribute. Concerning
verifying of this timestamp you should do the same concatenation, but throw
away all archive timestamps with time later then in the timestamp being
verified from unsignedAttrs element and encode it over again.
Pavel Smirnov
Crypto-Pro
Tel./Fax: +7 495 780-4820
WWW: <http://www.cryptopro.ru/> http://www.CryptoPro.ru
e-mail: <mailto:spv(_at_)CryptoPro(_dot_)ru> spv(_at_)CryptoPro(_dot_)ru
From: Yasir Khan [mailto:yasir(_dot_)khan(_at_)ascertia(_dot_)com]
Sent: Thursday, July 03, 2008 8:07 PM
To: Смирнов Павел Владимирович; ietf-smime(_at_)imc(_dot_)org
Subject: RE: Using Signature Policy in RFC-5126
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!
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Development Manager
Ascertia Limited
<http://www.ascertia.com/> www.ascertia.com
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From: owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org
[mailto:owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org]
On Behalf Of Pavel V. Smirnov
Sent: Thursday, June 26, 2008 1:04 PM
To: 'Yasir Khan'; ietf-smime(_at_)imc(_dot_)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: <mailto:spv(_at_)CryptoPro(_dot_)ru> spv(_at_)CryptoPro(_dot_)ru
From: owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org
[mailto:owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org]
On Behalf Of Yasir Khan
Sent: Thursday, June 26, 2008 12:19 PM
To: Смирнов Павел Владимирович; ietf-smime(_at_)imc(_dot_)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(_dot_)ru]
Sent: Wednesday, June 25, 2008 4:07 PM
To: 'Yasir Khan'; ietf-smime(_at_)imc(_dot_)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: <mailto:spv(_at_)CryptoPro(_dot_)ru> spv(_at_)CryptoPro(_dot_)ru
From: owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org
[mailto:owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org]
On Behalf Of Yasir Khan
Sent: Wednesday, June 25, 2008 2:43 PM
To: ietf-smime(_at_)imc(_dot_)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/>
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