i2pd/core/crypto/hmac.h

#ifndef HMAC_H__
#define HMAC_H__

#include <inttypes.h>
#include <string.h>
#define CRYPTOPP_ENABLE_NAMESPACE_WEAK 1
#include <cryptopp/md5.h>
#include "Identity.h"

namespace i2p
{
namespace crypto
{
    const uint64_t IPAD = 0x3636363636363636;
    const uint64_t OPAD = 0x5C5C5C5C5C5C5C5C;           

    typedef i2p::data::Tag<32> MACKey;
        
    inline void HMACMD5Digest (uint8_t * msg, size_t len, const MACKey& key, uint8_t * digest)
    // key is 32 bytes
    // digest is 16 bytes
    // block size is 64 bytes   
    {
        uint64_t buf[256];
        // ikeypad
        buf[0] = key.GetLL ()[0] ^ IPAD; 
        buf[1] = key.GetLL ()[1] ^ IPAD; 
        buf[2] = key.GetLL ()[2] ^ IPAD; 
        buf[3] = key.GetLL ()[3] ^ IPAD; 
        buf[4] = IPAD; 
        buf[5] = IPAD; 
        buf[6] = IPAD; 
        buf[7] = IPAD;      
        // concatenate with msg
        memcpy (buf + 8, msg, len);
        // calculate first hash
        uint8_t hash[16]; // MD5
        CryptoPP::Weak1::MD5().CalculateDigest (hash, (uint8_t *)buf, len + 64);
        
        // okeypad          
        buf[0] = key.GetLL ()[0] ^ OPAD; 
        buf[1] = key.GetLL ()[1] ^ OPAD; 
        buf[2] = key.GetLL ()[2] ^ OPAD; 
        buf[3] = key.GetLL ()[3] ^ OPAD; 
        buf[4] = OPAD; 
        buf[5] = OPAD; 
        buf[6] = OPAD; 
        buf[7] = OPAD; 
        // copy first hash after okeypad        
        memcpy (buf + 8, hash, 16);
        // fill next 16 bytes with zeros (first hash size assumed 32 bytes in I2P)
        memset (buf + 10, 0, 16);           
        
        // calculate digest
        CryptoPP::Weak1::MD5().CalculateDigest (digest, (uint8_t *)buf, 96);
    }
}
}

#endif