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Server-Side Encryption

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Last updated: 2026-03-05 17:02:48

Introduction

This document provides instructions on how to enable server-side encryption when objects are uploaded. Server-side encryption keys are categorized into three types:
COS managed encryption key
customer-provided encryption key
KMS managed encryption key

Preliminary Preparation

Create CosAPI

Before calling the COS API, you must first create an instance of CosAPI to make subsequent call requests.
qcloud_cos::CosAPI InitCosAPI() {
    uint64_t appid = 12500000000;
    std::string region = "ap-guangzhou";// Region of the bucket, see https://www.tencentcloud.com/document/product/436/62?from_cn_redirect=1
    std::string secret_id = "************************************"; // User's SecretId. It is recommended to use sub-account keys, with authorization following the least privilege principle to mitigate usage risks. For information on how to obtain sub-account keys, see https://www.tencentcloud.com/document/product/598/37140?from_cn_redirect=1
    std::string secret_key = "***********************************"; // User's SecretKey. It is recommended to use sub-account keys, with authorization following the least privilege principle to mitigate usage risks. For information on how to obtain sub-account keys, see https://www.tencentcloud.com/document/product/598/37140?from_cn_redirect=1
        
    qcloud_cos::CosConfig config(appid, tmp_secret_id, tmp_secret_key, region);
    qcloud_cos::CosAPI cos_tmp(config);
    return cos_tmp;
}

Create CosAPI Using a Temporary Key

To access COS with a temporary key, you need to create a CosAPI instance using the temporary key.
qcloud_cos::CosAPI InitCosAPI() {
    // You need to have obtained the temporary key results: tmp_secret_id, tmp_secret_key,
    // For generating temporary keys, see https://www.tencentcloud.com/document/product/436/14048?from_cn_redirect=1#cos-sts-sdk
    uint64_t appid = 12500000000;
    std::string region = "ap-guangzhou";
    std::string tmp_secret_id = "************************************";
    std::string tmp_secret_key = "***********************************";
    std::string tmp_token = "token";
    
    qcloud_cos::CosConfig config(appid, tmp_secret_id, tmp_secret_key, region);
    config.SetTmpToken(tmp_token);
    qcloud_cos::CosAPI cos_tmp(config);
    return cos_tmp;
}

Use Case

Using COS Managed Encryption Key for Server-Side Encryption (SSE-COS) to Protect Data

Tencent Cloud COS manages the master key and data. COS automatically encrypts your data when it is written to the data center and decrypts it when you access the data. Currently, AES-256 encryption using the COS master key is supported for data protection.
void PutObjectByFileDemo(qcloud_cos::CosAPI& cos) {
    std::string object_name = "test.txt";
    std::string file_path = "./test_file/text.txt";
    qcloud_cos::PutObjectByFileReq req(bucket_name, object_name, file_path);
    req.SetXCosServerSideEncryption("AES256");
    qcloud_cos::PutObjectByFileResp resp;
    qcloud_cos::CosResult result = cos.PutObject(req, &resp);


    std::cout << "====================PutObjectByFile======================" << std::endl;
    PrintResult(result, resp);
    std::cout << "=========================================================" << std::endl;
}

Use Server-Side Encryption with Customer-Provided Encryption Keys (SSE-C) to Protect Data

The encryption key is provided by the user. When objects are uploaded, COS uses the user-provided encryption key to perform AES-256 encryption on the data.
Note:
The service running this encryption must use HTTPS requests.
User must provide a 32-byte string as the key, which supports combinations of digits, letters, and characters, but does not support Chinese characters.
If a key is set for encryption when a file is uploaded, then when using GET (download) or HEAD (query) operations on the source object, the same key must be included in the request for it to be processed successfully.
void PutObjectByFileDemo(qcloud_cos::CosAPI& cos) {
    std::string object_name = "test.txt";
    std::string file_path = "./test_file/text.txt";
    qcloud_cos::PutObjectByFileReq req(bucket_name, object_name, file_path);
    req.SetHttps();
    req.TurnOffComputeConentMd5();
    req.AddHeader("x-cos-server-side-encryption-customer-algorithm", "AES256");  // Server-side encryption algorithm, currently only supports AES256
    req.AddHeader("x-cos-server-side-encryption-customer-key","key"); // Base64-encoded server-side encryption key, e.g., MDEyMzQ1Njc4OUFCQ0RFRjAxMjM0NTY3ODlBQkNERUY=
    req.AddHeader("x-cos-server-side-encryption-customer-key-MD5","key-MD5"); // MD5 hash value of the server-side encryption key, Base64-encoded, e.g., U5L61r7jcwdNvT7frmUG8g==
    // The Base64 encoding of the MD5 hash value must be calculated based on the binary-encoded MD5.
    qcloud_cos::PutObjectByFileResp resp;
    qcloud_cos::CosResult result = cos.PutObject(req, &resp);


    std::cout << "====================PutObjectByFile======================" << std::endl;
    PrintResult(result, resp);
    std::cout << "=========================================================" << std::endl;
}
void GetObjectByFileDemo(qcloud_cos::CosAPI& cos) {
    std::string object_name = "test.txt";
    std::string file_path = "./test_file/text2.txt";
    qcloud_cos::GetObjectByFileReq req(bucket_name, object_name, file_path);
    req.SetHttps();
    req.SetCheckMD5(false);
    req.AddHeader("x-cos-server-side-encryption-customer-algorithm", "AES256");  // Server-side encryption algorithm, currently only supports AES256
    req.AddHeader("x-cos-server-side-encryption-customer-key","key"); // Base64-encoded server-side encryption key, e.g., MDEyMzQ1Njc4OUFCQ0RFRjAxMjM0NTY3ODlBQkNERUY=
    req.AddHeader("x-cos-server-side-encryption-customer-key-MD5","key-MD5"); // MD5 hash value of the server-side encryption key, Base64-encoded, e.g., U5L61r7jcwdNvT7frmUG8g==
    qcloud_cos::GetObjectByFileResp resp;


    qcloud_cos::CosResult result = cos.GetObject(req, &resp);
    std::cout << "===================GetObjectResponse=====================" << std::endl;
    PrintResult(result, resp);
    std::cout << "=========================================================" << std::endl;
}

Using Server-Side Encryption With KMS Managed Encryption Key (SSE-KMS) to Protect Data

SSE-KMS encryption refers to server-side encryption using KMS managed keys. KMS is a security management service launched by Tencent Cloud, which uses third-party certified Hardware Security Modules (HSM) to generate and protect keys. It helps users easily create and manage keys, meeting their key management needs for multiple applications and business scenarios while fulfilling regulatory and compliance requirements. For instructions on activating the KMS service, see Server-Side Encryption Overview.
void PutObjectByFileDemo(qcloud_cos::CosAPI& cos) {
    std::string object_name = "test.txt";
    std::string file_path = "./test_file/text.txt";
    qcloud_cos::PutObjectByFileReq req(bucket_name, object_name, file_path);
    req.SetXCosServerSideEncryption("cos/kms");
    req.TurnOffComputeConentMd5();
    req.AddHeader("x-cos-server-side-encryption-cos-kms-key-id","key-id"); // Specifies the KMS Customer Master Key (CMK). If not specified, the CMK created by default for COS will be used
    req.AddHeader("x-cos-server-side-encryption-context","context"); // Specifies the encryption context, which is the Base64-encoded JSON-formatted key-value pairs. For example, eyJhIjoiYXNkZmEiLCJiIjoiMTIzMzIxIn0=

    qcloud_cos::PutObjectByFileResp resp;
    qcloud_cos::CosResult result = cos.PutObject(req, &resp);


    std::cout << "====================PutObjectByFile======================" << std::endl;
    PrintResult(result, resp);
    std::cout << "=========================================================" << std::endl;
}

void GetObjectByFileDemo(qcloud_cos::CosAPI& cos) {
    std::string object_name = "test.txt";
    std::string file_path = "./test_file/text2.txt";
    qcloud_cos::GetObjectByFileReq req(bucket_name, object_name, file_path);
    req.SetHttps();
    req.SetCheckMD5(false);
    qcloud_cos::GetObjectByFileResp resp;


    qcloud_cos::CosResult result = cos.GetObject(req, &resp);
    std::cout << "===================GetObjectResponse=====================" << std::endl;
    PrintResult(result, resp);
    std::cout << "=========================================================" << std::endl;
}

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