Thanks a tonne, I will try it out
On Oct 21, 8:16 pm, "Wei Dai" <[EMAIL PROTECTED]> wrote:
> Replace the line "CryptoPP::StringSource( message, true, verifierFilter );"
> with:
>
> verifierFilter->Put(part1, length1);
> verifierFilter->Put(part2, length2);
> // ...
> verifierFilter->MessageEnd();
>
> --------------------------------------------------
> From: "Cyptmon" <[EMAIL PROTECTED]>
> Sent: Sunday, October 21, 2007 3:09 PM
> To: "Crypto++ Users" <[EMAIL PROTECTED]>
> Subject: Re: RSA and SHA-1 speeds
>
>
>
> > 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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