====================
== Hi, I'm Vimiix ==
====================
Practice makes perfect (ง •̀_•́)ง

Golang实现Google在RTB广告中价格加密方案

solution golang rtb

RTB

RTB 广告是一种实时竞价广告,就是在针对每个广告位有展示机会的时候,会实时多方竞价,价格最有优势的广告主会竞得这次展示机会,在媒体测在拿到素材的时候,需将本次成交的价格,上报给指定的监控服务器,这时就需要将实时价格按照指定的加密方案加密后,替换 GET 链接中的请求参数中的价格宏来上报。

官方给出的源代码有 Java 和 C++ 版本, 下载地址: https://code.google.com/archive/p/privatedatacommunicationprotocol/source/default/source

本文主要通过 golang 来实现的 google 的价格加密方案

Source Code

package main

/*
golang 实现 google 的rtb 价格加密方案
https://developers.google.com/authorized-buyers/rtb/response-guide/decrypt-price#encryption-scheme
*/

import (
	"crypto/hmac"
	"crypto/md5"
	"crypto/sha1"
	"encoding/base64"
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"hash"
	"math"
	"strings"
)

const (
	PayloadSize    = 8
	InitVectorSize = 16
	SignatureSize  = 4
	EKey           = ""
	IKey           = ""
	UTF8           = "utf-8"
)

func AddBase64Padding(base64Input string) string {
	var b64 string
	b64 = base64Input
	if i := len(b64) % 4; i != 0 {
		b64 += strings.Repeat("=", 4-i)
	}
	return b64
}

func CreateHmac(key, mode string, isBase64 bool) (hash.Hash, error) {
	var b64DecodedKey []byte
	var k []byte
	var err error
	if isBase64 {
		b64DecodedKey, err = base64.URLEncoding.DecodeString(AddBase64Padding(key))
		if err == nil {
			key = string(b64DecodedKey[:])
		}
	}
	if mode == UTF8 {
		k = []byte(key)
	} else {
		k, err = hex.DecodeString(key)
	}
	if err != nil {
		return nil, err
	}
	return hmac.New(sha1.New, k), nil
}

func HmacSum(_hmac hash.Hash, buf []byte) []byte {
	_hmac.Reset()
	_hmac.Write(buf)
	return _hmac.Sum(nil)
}

func Hmac(key string, buf []byte) ([]byte, error) {
	_hmac, err := CreateHmac(key, UTF8, true)
	if err != nil {
		err = fmt.Errorf("jzt/encrypt: create hmac error, %s", err.Error())
		return nil, err
	}
	return HmacSum(_hmac, buf), nil
}

func EncryptPrice(price float64) (string, error) {
	var (
		iv         = make([]byte, InitVectorSize)
		encoded    = make([]byte, PayloadSize)
		signature  = make([]byte, SignatureSize)
		priceBytes = make([]byte, PayloadSize)
	)

	sum := md5.Sum([]byte(""))
	copy(iv[:], sum[:])

	// pad = hmac(e_key, iv)  // first 8 bytes
	pad, err := Hmac(EKey, iv[:])
	if err != nil {
		return "", err
	}
	pad = pad[:PayloadSize]

	bits := math.Float64bits(price)
	binary.BigEndian.PutUint64(priceBytes, bits)
	// enc_price = pad <xor> price
	for i := range priceBytes {
		encoded[i] = pad[i] ^ priceBytes[i]
	}

	// signature = hmac(i_key, data || iv), first 4 bytes
	sig, err := Hmac(IKey, append(priceBytes[:], iv[:]...))
	if err != nil {
		return "", err
	}
	signature = sig[:SignatureSize]

	// final_message = WebSafeBase64Encode( iv || enc_price || signature )
	finalMessage := strings.TrimRight(
		base64.URLEncoding.EncodeToString(append(append(iv[:], encoded[:]...), signature[:]...)),
		"=")
	return finalMessage, nil
}

func DecryptPrice(finalMessage string) (float64, error) {
	var err error
	var errPrice float64
	encryptedPrice := AddBase64Padding(finalMessage)
	decoded, err := base64.URLEncoding.DecodeString(encryptedPrice)
	if err != nil {
		return errPrice, err
	}
	var (
		iv         = make([]byte, InitVectorSize)
		p          = make([]byte, PayloadSize)
		signature  = make([]byte, SignatureSize)
		priceBytes = make([]byte, PayloadSize)
	)

	copy(iv[:], decoded[0:16])
	copy(p[:], decoded[16:24])
	copy(signature[:], decoded[24:28])

	pad, err := Hmac(EKey, iv[:])
	if err != nil {
		return errPrice, err
	}
	pad = pad[:PayloadSize]
	for i := range p {
		priceBytes[i] = pad[i] ^ p[i]
	}

	sig, err := Hmac(IKey, append(priceBytes[:], iv[:]...))
	if err != nil {
		return errPrice, err
	}
	sig = sig[:SignatureSize]
	for i := range sig {
		if sig[i] != signature[i] {
			return errPrice, fmt.Errorf("jzt/decrypt: Failed to decrypt, got:%s ,expect:%s", string(sig), string(signature))
		}
	}

	price := math.Float64frombits(binary.BigEndian.Uint64(priceBytes))
	return price, nil
}


func main() {
	var result string
	var err error
	var price float64
	result, err = EncryptPrice(0.11)
	if err != nil {
		err = fmt.Errorf("Encryption failed. Error : %s", err)
	}
	fmt.Println(result)

	price, err = DecryptPrice("1B2M2Y8AsgTpgAmY7PhCfumh5TxN_8-DUn4uHg")
	if err != nil {
		err = fmt.Errorf("Encryption failed. Error : %s", err)
	}
	fmt.Println(price)
}