Re: Computing Hash

From: Param (Param_at_discussions.microsoft.com)
Date: 09/09/04 

Date: Thu, 9 Sep 2004 01:43:04 -0700

pbSignature is actual signature in the der format
and fileLen is the length of the pbSignature.
from this signature only i got the certificate and publickey
as u told if the parameters are wrong what extra check i have to perform

the same signature i am able to verify with the
CryptVerifyDetachedMessageSignature

"Valery Pryamikov" wrote:

> That means that you passed parameters wrong.
> btw, what fileLen has to do with the length of pbSignature? if you have
> detached signature, in separate file, it probably encoded with ASN1 and
> filelen would not be size of signature, but size of encoded blob including
> tags, oid and envelope. You have to pass signature only (large integer
> number) in little-endian format to the CryptVerifySignature. if parameters
> are passed correctly and signature matches, then api is guaranteed to work.
>
> -Valery.
> http://www.harper.no/valery
>
> "Param" <Param@discussions.microsoft.com> wrote in message
> news:AA0BAAD9-ECDA-47D9-A743-E0485ACFF8D2@microsoft.com...
> > Hello,
> > I am getting NTE_BAD_SIGNATURE error in the CryptVerifySignature
> >
> > CryptVerifySignature(hHash,
> > pbSignature,
> > fileLen,
> > hPubKey,
> > NULL,
> > 0))
> >
> >
> > "Valery Pryamikov" wrote:
> >
> >> Just call CryptHashData while as you streaming your data and pass hash to
> >> CryptVerifySignature.
> >> You only have to make sure that you pass pbSignature in little endian
> >> format
> >> (ASN1 encodded format holds it in big-endian, so you just need to reverse
> >> bytes)
> >>
> >> -Valery.
> >> http://www.harper.no/valery
> >>
> >> "Param" <Param@discussions.microsoft.com> wrote in message
> >> news:BAFF8FE3-86F3-4CA4-A3C9-87E0DA0B9970@microsoft.com...
> >> > nothing
> >> > i am asking about signature verification
> >> >
> >> > "Valery Pryamikov" wrote:
> >> >
> >> >> What stops you from calling CryptHashData while as you streaming your
> >> >> data?
> >> >>
> >> >> -Valery.
> >> >> http://www.harper.no/valery
> >> >>
> >> >> "Param" <Param@discussions.microsoft.com> wrote in message
> >> >> news:04630EF7-172B-4D8E-A0C0-023A855DCF5D@microsoft.com...
> >> >> > That means i need to call CryptHashData in a loop until i pass the
> >> >> > last
> >> >> > chunk
> >> >> > of data.
> >> >> > need to set any flag for tha last chunk of data.
> >> >> >
> >> >> > Actually my requirement is different.
> >> >> > I need to verify a large file signature.
> >> >> > I am getting all the details from the detached signature(pkcs7).
> >> >> > signer
> >> >> > info
> >> >> > etc..
> >> >> > I am not able to check for the data intigrity part(hash checking)
> >> >> > bcs
> >> >> > of
> >> >> > the
> >> >> > huge
> >> >> > amount of the data .
> >> >> > Is there any other method for doing so(streaming)
> >> >> > thanx in adv....
> >> >> >
> >> >> >
> >> >> >
> >> >> >
> >> >> > "Valery Pryamikov" wrote:
> >> >> >
> >> >> >> Hi,
> >> >> >> you simply create hash with CryptCreateHash, call CryptHashData
> >> >> >> passing
> >> >> >> it
> >> >> >> with chunks of data while as you read it and call
> >> >> >> CryptGetHashParam(...,
> >> >> >> HP_HASHVAL, ...) to get hash value when you ready with feeding data
> >> >> >> in.
> >> >> >>
> >> >> >> -Valery.
> >> >> >> http://www.harper.no/valery
> >> >> >>
> >> >> >> "Param" <Param@discussions.microsoft.com> wrote in message
> >> >> >> news:B3EE380A-F720-41A2-866D-9F201EBBD145@microsoft.com...
> >> >> >> > Hi,
> >> >> >> > How do i create hash of a 500MB using CryptoAPI?
> >> >> >>
> >> >> >>
> >> >> >>
> >> >>
> >> >>
> >> >>
> >>
> >>
> >>
>
>
>

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