如何在HMAC-SHA1 Crypto ++实现中使用自定义密钥

Question

I want to implement OAuth 1.0 protocol in my C++ project. In order to create OAuth signature I need to implement HMAC-SHA1 algorithm where key and text will be some string created according to OAuth specification.

I want to use Crypto++ library for implementing HMAC-SHA1. I found this HMAC-SHA1 example on wiki of project:

AutoSeededRandomPool prng;

SecByteBlock key(16);
prng.GenerateBlock(key, key.size());

string plain = "HMAC Test";
string mac, encoded;

/*********************************\
\*********************************/

// Pretty print key
encoded.clear();
StringSource(key, key.size(), true,
    new HexEncoder(
        new StringSink(encoded)
    ) // HexEncoder
); // StringSource

cout << "key: " << encoded << endl;
cout << "plain text: " << plain << endl;

/*********************************\
\*********************************/

try
{
    HMAC< SHA256 > hmac(key, key.size());

    StringSource(plain, true, 
        new HashFilter(hmac,
            new StringSink(mac)
        ) // HashFilter      
    ); // StringSource
}
catch(const CryptoPP::Exception& e)
{
    cerr << e.what() << endl;
    exit(1);
}

/*********************************\
\*********************************/

// Pretty print
encoded.clear();
StringSource(mac, true,
    new HexEncoder(
        new StringSink(encoded)
    ) // HexEncoder
); // StringSource

cout << "hmac: " << encoded << endl;

But I can't understand how instead of random generated string use my created key . I tried just create:

string key=...; //string generated by OAuth specification;

But then appear compiling errors. However when I write:

string plain=...; //string generated by OAuth specification;

Then there is no errors.

And what key length I need to specify? Because I will have keys of different lengths (with 48 and maybe 96 symbols).

Answer 1

It appears there are a few things you need to get familiar with. (Sorry I can't help because I've never had to do it).

First is the Security Architecture. You can find some reading at Beginner's Guide to OAuth – Part III : Security Architecture .

Second is the HMAC-SHA1 signature and format. You can find the overview at OAuth Core HMAC-SHA1 .

Third, you need to understand OAuth's encoding and presentation format. You can find some reading at OAuth Core Parameter Encoding .

---

To answer some of your questions:

You will need to parse and decode the parameters to get the key, signed data, and signature. So you will need to parse and decode three values: oauth_key , oauth_data and oauth_signature .

Then, you will set up your Crypto++ HMAC key as follows.

SecByteBlock key(SHA1::BLOCKSIZE);
memcpy(key.data(), key.size(), oauth_key);

After that, you would verify with the following:

byte oauth_key[] = ...; // Your parsed and decoded key
string oauth_data = ...; // Your parsed and decoded data
string oauth_signature = ...; // // Your parsed and decoded signature

try
{
    SecByteBlock key(SHA1::BLOCKSIZE);
    memcpy(key.data(), key.size(), oauth_key);

    HMAC< SHA1 > hmac(key, key.size());
    const int flags = HashVerificationFilter::THROW_EXCEPTION | HashVerificationFilter::HASH_AT_END;

    StringSource ss(oauth_data + oauth_signature + mac, true, 
        new HashVerificationFilter(hmac, NULL, flags)
    ); // StringSource

    cout << "Verified message" << endl;
}
catch(const CryptoPP::Exception& e)
{
    // Handle failure
    cerr << e.what() << endl;        
}

---

Another thing Crypto++ might be able to help with is Base64 decoding. Below is from the HexDecoder wiki page , but it applies to Base64Decoder because the encoders and decoders use the same interface.

string encoded = ...;
string decoded;

StringSource ss(encoded,
    new HexDecoder(
        new StringSink(decoded)
    ) // HexDecoder
); // StringSource

So your code would be:

string encoded = ...;
string decoded;

StringSource ss(encoded,
    new Base64Decoder(
        new StringSink(decoded)
    ) // Base64Decoder
); // StringSource

The above uses Crypto++'s pipline interface, where data flows from a source to a sink. You can also do it in a more "C" like manner using Put and Get on the Base64Decoder object:

string encoded = ...;
string decoded;

Base64Decoder decoder;

decoder.Put( (byte*)encoded.data(), encoded.size() );
decoder.MessageEnd();

word64 size = decoder.MaxRetrievable();
if(size && size <= SIZE_MAX)
{
    decoded.resize(size);       
    decoder.Get((byte*)decoded.data(), decoded.size());
}

Answer 2

I was tasked with a very similar task. Do two-legged OAuth 1.0a in C++. Two-legged because there is no user involved in the process, only the client and the server. As described in: http://oauth.googlecode.com/svn/spec/ext/consumer_request/1.0/drafts/2/spec.html

The complete proof of concept including parsing and decoding the parameters can be found at: https://gist.github.com/duedal/a197fc9f6dc1ad59f08c

Should be easy to build on this to complete it. Mainly need to validate the timestamp+nonce, and of course tie into your project.