背景
在hive数据库的kerberos加密协议解析中，加密套件默认是ETYPE_AES256_CTS_HMAC_SHA1_96。解密后的cipher部分是asn.1编码过的，拿到想要的字段就需要解密tlv协议。TLV三元组<Type, Length,Value>。
描述Value部分所占字节的个数，编码格式分两类：定长方式（DefiniteForm）和不定长方式（IndefiniteForm）。定长模式中，根据长度是否超过一个字节（127）分短/长形式。
短：0-127，二进制表示01111 111，第8位是0，即length用一个字节即可
长：>127，二进制表示10000000，第8位是1，即length需要用多个字节表示，此时0-7位用来描述length值需要占用的字节数。
Example
//
// Created by Serrini on 2022/1/6.
//
#ifndef TEST021_HDFS_TLV_H
#define TEST021_HDFS_TLV_H
#include <iostream>
class TLV{
public:
TLV();
int ParseTLV(const unsigned char* data, int len);
void SkipHead(int len);
void SkipTLV(int len);
void Clear();
public:
int m_type;
int m_length;
unsigned char* m_data;
int m_headLen;
unsigned char* m_skipPtr;
int m_skipLength;
};
#endif //TEST021_HDFS_TLV_H
//
// Created by Serrini on 2022/1/6.
//
#include "TLV.h"
TLV::TLV():m_type(0) , m_length(0), m_data(NULL), m_headLen(0), m_skipPtr(NULL), m_skipLength(0){
}
int TLV::ParseTLV(const unsigned char *data, int len) {
if((data == NULL) || (len < 2)){
printf("Check tlv data and len failed\n");
return -1;
}
m_type = data[0];
if(data[1] > 0x7F){
m_length = 0;
if(len > (1 + 1 + (data[1] - 0x80))){
int i = 0;
m_data = (unsigned char*)data + 1 + 1 + (data[1] - 0x80);
for(i = 0; i < (data[1] - 0x80); ++i){
m_length = m_length * 256 + data[1 + 1 + i];
}
m_headLen = 1 + 1 + (data[1] - 0x80);
}else{
printf("Check value length len failed, length len:%d, len:%d\n", (1 + 1 + (data[1] - 0x80)), len);
return -1;
}
}else{
m_headLen = 1 + 1;
m_length = data[1];
m_data = (unsigned char*)data + 1 + 1;
}
if((m_headLen + m_length) > len){
printf("Check value length and package length failed, tlv:%d, package len:%d\n", (m_headLen + m_length), len);
return -1;
}
printf("type:%x, length:%d, head length:%d\n", m_type, m_length, m_headLen);
return 0;
}
void TLV::SkipHead(int len){
m_skipPtr = m_data;
m_skipLength = len - m_headLen;
if(m_skipLength <= 0){
m_skipPtr = NULL;
m_skipLength = 0;
printf("[SkipHead]:Skip head length failed. len:%d, head len:%d\n", len, m_headLen);
}
}
void TLV::SkipTLV(int len){
m_skipPtr = m_data + m_length;
m_skipLength = len - m_headLen - m_length;
if(m_skipLength <= 0){
m_skipPtr = NULL;
m_skipLength = 0;
printf("[SkipTLV]:Skip head length failed. len:%d, head len:%d, value length: %d\n", len, m_headLen, m_length);
}
}
void TLV::Clear(){
m_type = 0;
m_length = 0;
m_data = NULL;
m_headLen = 0;
m_skipLength = 0;
m_skipPtr = NULL;
}
