Value after cryptopp base64 encoding/decoding not the same

问题

I'm playing with cryptopp and have trouble with Base64 encoding/decoding.

In the following code hypothetically sig value should be equal tsig, but they are different on a last character (sig bigger then tsig by one symbol). I've tried also change insertLineBreaks parameter in Base64Encoder but the result is same. ...

RSASSA_PKCS1v15_SHA_Signer privkey(privateKey);
SecByteBlock sbbSignature(privkey.SignatureLength());
privkey.SignMessage(rng, (byte const*) strContents.data(),
    strContents.size(),sbbSignature);

Base64Encoder b(new StringSink(signedData));
b.Put(sbbSignature.begin(), sbbSignature.size());

string sig;
StringSink sinksig(sig);
sinksig.Put(sbbSignature.begin(), sbbSignature.size());

string tsig;
StringSource ss(signedData, true, 
    new Base64Decoder(
        new StringSink(tsig)
    )
);

Where is my mistake?

回答1:

b.Put(sbbSignature.begin(), sbbSignature.size());

Try:

b.Put(sbbSignature.begin(), sbbSignature.size());
b.MessgeEnd();

This does not quite look right:

SecByteBlock sbbSignature(privkey.SignatureLength());
privkey.SignMessage(rng, (byte const*) strContents.data(),
    strContents.size(),sbbSignature);

Try:

size_t maxLength = privkey.MaxSignatureLength();
SecByteBlock sbbSignature(maxLength);

size_t signatureLength = privkey.SignMessage(rng,
    (byte const*) strContents.data(), strContents.size(),
    sbbSignature);

if(maxLength != signatureLength)
    sbbSignature.resize(signatureLength);

There's an example on the Crypto++ wiki at RSA Signature Scheme with Appendix, but I think its wrong after looking at it.

来源：https://stackoverflow.com/questions/23095254/value-after-cryptopp-base64-encoding-decoding-not-the-same

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c++

base64

crypto++