RSA decryption on the signature that we have and compare it with the
hash we generated to be more precise
Thanks
On Oct 21, 6:09 pm, Cyptmon <[EMAIL PROTECTED]> wrote:
> 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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