Thanks Wei Dai for that message. This will ensure that I compute the
signature on 512 bit blocks, however, the code using VerifierFilter is
something like this
CryptoPP::VerifierFilter *verifierFilter = new
CryptoPP::VerifierFilter(pub);
verifierFilter->Put(signature, pub.SignatureLength());
CryptoPP::StringSource( message, true, verifierFilter );
if( false == verifierFilter->GetLastResult() )
{
return false;
}
else
{
return true;
}
(Taken from examples on Wiki)
Now this again takes the entire message as one of the parameters
right, is there a piecemeal way of doing this the way we generated the
signature, say something which generates the hash using update and
final methods and finally use RSA decryption using the public key that
we have?
Thanks again
On Oct 21, 5:08 pm, "Wei Dai" <[EMAIL PROTECTED]> wrote:
> You can do this using a SignerFilter object, or using the
> NewSignatureAccumulator() and Sign() functions of the Signer class instead
> of the SignMessage() function. (SignerFilter basically does the latter for
> you.) For verification, use VerifierFilter.
>
> // untested sample code
> RSASS<PKCS1v15, SHA>::Signer priv;
> // initialize priv with key here
> std::string sig;
> SignerFilter f(rng, priv, new StringSink(sig));
> f.Put(part1, length1);
> f.Put(part2, length2);
> // ...
> f.MessageEnd();
> // sig now contains the signature
>
> --------------------------------------------------
> From: "Cyptmon" <[EMAIL PROTECTED]>
> Sent: Sunday, October 21, 2007 12:32 PM
> To: "Crypto++ Users" <[EMAIL PROTECTED]>
> Subject: Re: RSA and SHA-1 speeds
>
>
>
> > Is there a way to calculate the message digest using a chained
> > approach, wherein, I calculate the hash of data 512 bits at a time,
> > use this hash as an IV for the next round and finally get the hash of
> > the large chunk of data. At any time I do not want to be working on
> > more than 512 bits of data. Can I get this digest and then sign it
> > and subsequently verify it ? Or do we always have to pass the entire
> > data to the Signer class?
>
> > On Oct 17, 5:43 pm, Cyptmon <[EMAIL PROTECTED]> wrote:
> >> Thanks everyone
>
> >> I had yet another question
>
> >> Say I use SHA-256 for computing the hash for verifying the signature.
> >> The data I need to sign is nearly 30MB, I just want to be sure that
> >> the implementation follows an incremental hash sort of a thing,
> >> wherein, the hash of one 512 bit block feeds to the next computation
> >> as the IV. Am I right on this?
>
> >> Thanks
>
> >> On Oct 11, 3:44 pm, "Jeffrey Walton" <[EMAIL PROTECTED]> wrote:
>
> >> > Hi Cyptmon,
>
> >> > > I get the private exponent as 1024 bits, the public
> >> > > exponent is the smaller one and it is 17 always.
>
> >> > You are interpreting incorrectly: 1024 is the size of the modulous. 17
> >> > is the Public Exponent.
>
> >> > See the dump keys example athttp://www.cryptopp.com/wiki/RSA
>
> >> > > PS: I hope GenerateRandomWithKeySize
>
> >> > One possible way to generate keys...
>
> >> > Jeff
>
> >> > On 10/11/07, Cyptmon <[EMAIL PROTECTED]> wrote:
>
> >> > > Thanks for the replies, I am sorry I made a mistake, I get the
> >> > > private
> >> > > exponent as 1024 bits, the public exponent is the smaller one and it
> >> > > is 17 always. Why is it always 17 irrespective of the key size that I
> >> > > specify?
>
> >> > > Isnt the public key chosen as something that is relatively prime to
> >> > > Totient function of n (Phi (n ) where n is p * q)
>
> >> > > Thanks
>
> >> > > PS: I hope GenerateRandomWithKeySize is the right function to use to
> >> > > generate different sized keys for RSA as directed by the second
> >> > > argument passed to it
>
> >> > > [ SNIP ]
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