Note：

1. This document is only for the COS XML version.
2. It does not apply to POST Object requests over HTTP.

Overview

You can use COS with RESTful APIs, which support anonymous and signed HTTP requests. The COS server will authenticate the requester of signed requests.

• Anonymous request: an HTTP request that does not carry any authentication information, and is sent using RESTful APIs.
• Signed request: an HTTP request that carries a signature. The COS server will authenticate requesters and only execute requests initiated by authenticated ones. If the authentication fails, COS will return an error message and deny the request.

COS authenticates requesters using a custom solution based on Hash Message Authentication Code (HMAC).

Implementing Signature in SDK

Signatures are already implemented in COS SDKs, which means when you initiate requests or obtain signatures using an SDK, you can ignore the signature issue. To implement a signature by yourself or learn about the implementation of signatures in different programming languages, see the programming language−specific signature implementation file from the table below:

SDK	Signature Implementation File
Android SDK	COSXmlSigner.java
C SDK	cos_auth.c
C++ SDK	auth_tool.cpp
.NET(C#) SDK	IQCloudSigner.cs (class CosXmlSigner)
Go SDK	auth.go
iOS SDK	QCloudAuthentationV5Creator.m
Java SDK	COSSigner.java
JavaScript SDK	util.js (getAuth)
Node.js SDK	util.js (getAuth)
PHP SDK	Signature.php
Python SDK	cos_auth.py
Mini Program SDK	util.js (getAuth)

Generating a Signed URL

Currently, all COS SDKs can generate URLs that carry a signature valid for a period of time. The signature supports PUT and GET requests. Therefore, you can use the generated signed URL to upload/download objects directly without having to generate a signature separately.

• When generating a signed URL for uploads, you can also specify headers such as Content-Type and Content-MD5 to limit the media type/content to upload. For the configurations of request headers related to uploads, please see PUT Object.
• When generating a signed URL for downloads, you can also specify response-xxx so that you can temporarily modify response headers upon download. For the configurations of request parameters related to downloads, please see GET Object.

Find the pre-signed URL document corresponding to your SDK language from the table below:

SDK	Pre-Signed URL Document
Android SDK	Generating a Pre-Signed URL
C SDK	Pre-Signed URL
C++ SDK	Pre-Signed URL
.NET(C#) SDK	Generating a Pre-Signed URL
Go SDK	Pre-Signed URL
iOS SDK	Generating a Pre-Signed URL
Java SDK	Pre-Signed URL
JavaScript SDK	Pre-Signed URL
Node.js SDK	Pre-Signed URL
PHP SDK	Pre-Signed URL
Python SDK	Pre-Signed URL
Mini Program SDK	Pre-Signed URL

Use Cases

If a COS object needs to be published to the public, you will usually need to set this object to public-read/private-write (everyone can read the object but only the ACL-specified account can write to it). After this, you can use the ACL policy together with the API request signature to authenticate requesters and control the permissions and validity period of operations.

Note：

The API request signature described in this document is already included in the SDK. Perform the steps below only if you want to redevelop based on the native APIs.

You can secure your API request as follows for the use case above.

1. Authenticate requester: verifies the identity of the requester by their unique ID and key.
2. Prevent data tempering during transfer: signs and verifies data to ensure its integrity during transfer.
3. Prevent signature from being stolen: sets validity period for the signature to prevent it from being stolen or used repeatedly.

Preparations

1. Obtain APPID, SecretId, and SecretKey.
   They can be obtained on the Manage API Key page in the CAM console.
2. Determine the programming language.
   Supported languages include but are not limited to Java, PHP, .NET, C++, Node.js, and Python. You can determine the HMAC-SHA1, SHA1, and UrlEncode functions according to the programming language selected.
   The HMAC-SHA1 and SHA1 functions take UTF-8 encoded strings as input, and output lowercase hexadecimal strings, and UrlEncode is also based on UTF-8 encoding. Besides, the following printable special characters in the ASCII range should also be encoded:

Character	Decimal	Hex	Character	Decimal	Hex
(Space)	32	20	;	59	3B
!	33	21	<	60	3C
"	34	22	=	61	3D
#	35	23	>	62	3E
$	36	24	?	63	3F
%	37	25	@	64	40
&	38	26	[	91	5B
'	39	27	\	92	5C
(	40	28	]	93	5D
)	41	29	^	94	5E
*	42	2A	`	96	60
+	43	2B	{	123	7B
,	44	2C	|	124	7C
/	47	2F	}	125	7D
:	58	3A

Generating a Signature

Step 1. Generate KeyTime

1. Get the Unix StartTimestamp of the current time. It is the total number of seconds from January 1, 1970, 00:00:00 UTC (January 1, 1970, 08:00:00 Beijing time) till the current time.
2. Calculate the Unix EndTimestamp for the signature to expire according to StartTimestamp and the expected validity period of the signature.
3. Generate KeyTime by splicing the two timestamps above in StartTimestamp;EndTimestamp format (e.g., 1557902800;1557910000).

Step 2. Generate SignKey

Use HMAC-SHA1 with SecretKey as the key and KeyTime as the message to calculate the message digest (i.e., SignKey), which is a hash value in lowercase hexadecimal format, such as eb2519b498b02ac213cb1f3d1a3d27a3b3c9bc5f.

Step 3. Generate UrlParamList and HttpParameters

1. Traverse the HTTP request parameters to generate a key-to-value Map and a KeyList:
   • Encode keys using UrlEncode, and convert them to lowercase.
   • Encode values using UrlEncode. If a parameter does not take any value, its value is considered to be an empty string. For example, a request path /?acl is considered as /?acl=.

     Note：

     The parameters in an HTTP request are what comes after ? in the request path. For example, in the request path /?versions&prefix=example-folder%2F&delimiter=%2F&max-keys=10, the request parameters are versions&prefix=example-folder%2F&delimiter=%2F&max-keys=10.

2. Sort the KeyList in lexicographical order.
3. Splice all key-value pairs in the Map according to the order in KeyList in the format of key1=value1&key2=value2&key3=value3, which is the HttpParameters.
4. Splice all keys in the order of the KeyList· in the format of key1;key2;key3, which is the UrlParamList.

Examples

• Example 1:
  Request path: /?prefix=example-folder%2F&delimiter=%2F&max-keys=10
  UrlParamList: delimiter;max-keys;prefix
  HttpParameters: delimiter=%2F&max-keys=10&prefix=example-folder%2F

  Note：

  When the request is sent, the request parameters in the request path will also be URL-encoded. Therefore, do not repeat the URL encoding operation.

• Example 2:
  Request path: /exampleobject?acl
  UrlParamList: acl
  HttpParameters: acl=

Step 4. Generate HeaderList and HttpHeaders

1. Traverse the HTTP request parameters, and generate the key-to-value mapping Map and the key list KeyList, where keys are [URL-encoded](#.E5.87.86.E5.A4.87.E5.B7.A5 .E4.BD.9C) and converted to lowercase, and values are URL-encoded.
2. Sort the KeyList in lexicographical order.
3. Splice all key-value pairs in the Map according to the order in KeyList in the format of key1=value1&key2=value2&key3=value3, which is the HttpHeaders.
4. Splice all keys according to the order in KeyList in the format of key1;key2;key3, which is the HeaderList.

Examples

Request headers:

Host: examplebucket-1250000000.cos.ap-shanghai.myqcloud.com
Date: Thu, 16 May 2019 03:15:06 GMT
x-cos-acl: private
x-cos-grant-read: uin="100000000011"

Calculations:

• HeaderList = date;host;x-cos-acl;x-cos-grant-read
• HttpHeaders = date=Thu%2C%2016%20May%202019%2003%3A15%3A06%20GMT&host=examplebucket-1250000000.cos.ap-shanghai.myqcloud.com&x-cos-acl=private&x-cos-grant-read=uin%3D%22100000000011%22

Step 5. Generate HttpString

Generate HttpString based on HttpMethod, UriPathname, HttpParameters, and HttpHeaders in the format of HttpMethod\nUriPathname\nHttpParameters\nHttpHeaders\n.

Where,

• HttpMethod is converted to lowercase, such as get or put.
• UriPathname is the request path, such as / or /exampleobject.
• \n is a line break. If there is an empty string, the line breaks before and after it should be retained, for example, get\n/exampleobject\n\n\n.

Step 6. Generate StringToSign

Generate StringToSign based on KeyTime and HttpString in the format of sha1\nKeyTime\nSHA1(HttpString)\n.
Where,

• sha1 is a fixed string.
• \n is a line break.
• SHA1(HttpString) is the message digest (in lowercase hexadecimal format, such as 54ecfe22f59d3514fdc764b87a32d8133ea611e6) calculated with SHA1 and HttpString.

Step 7. Generate Signature

Use HMAC-SHA1 with SignKey (a string rather than the original binary) as the key and StringToSign as the message to calculate the message digest, which is Signature, for example, 01681b8c9d798a678e43b685a9f1bba0f6c0e012.

Step 8: generate a signature

Generate the actual signature based on SecretId, KeyTime, HeaderList, UrlParamList, and Signature in the following format:

q-sign-algorithm=sha1
&q-ak=SecretId
&q-sign-time=KeyTime
&q-key-time=KeyTime
&q-header-list=HeaderList
&q-url-param-list=UrlParamList
&q-signature=Signature

Note：

Line breaks in the sample above are for readability only and are not included in the actual signature.

Using a Signature

Signed HTTP requests sent to COS via RESTful APIs can pass the signature in the following ways:

1. Pass through a standard HTTP Authorization header, such as Authorization: q-sign-algorithm=sha1&q-ak=...&q-sign-time=1557989753;1557996953&...&q-signature=...
2. Pass as an HTTP request parameter (be sure to URL-encode), such as /exampleobject?q-sign-algorithm=sha1&q-ak=...&q-sign-time=1557989753%3B1557996953&...&q-signature=...

Note：

In the example above, ... are the signatures.

Using a Temporary Credential (Key)

If a temporary credential is used for signature calculation, the x-cos-security-token field should be specified when you send the request. The way to specify this field varies depending on how the signature is passed in.

1. If the signature is passed in using the standard HTTP Authorization header, specify x-cos-security-token as a request header as follows:

   Authorization: q-sign-algorithm=sha1&q-ak=...&q-sign-time=1557989753;1557996953&...&q-signature=...
   x-cos-security-token: ...
   

2. If the signature is passed in as an HTTP request parameter, specify x-cos-security-token as a request parameter as follows:

   /exampleobject?q-sign-algorithm=sha1&q-ak=...&q-sign-time=1557989753%3B1557996953&...&q-signature=...&x-cos-security-token=...
   

Note：

In the samples above, ... is the signature and access token.

Sample Codes

Pseudocode

KeyTime = [Now];[Expires]
SignKey = HMAC-SHA1([SecretKey], KeyTime)
HttpString = [HttpMethod]\n[HttpURI]\n[HttpParameters]\n[HttpHeaders]\n
StringToSign = sha1\nKeyTime\nSHA1(HttpString)\n
Signature = HMAC-SHA1(SignKey, StringToSign)

Sample of the message digest algorithm

The samples below illustrate how to call HMAC-SHA1 in different languages:

PHP

$sha1HttpString = sha1('ExampleHttpString');
$signKey = hash_hmac('sha1', 'ExampleKeyTime', 'YourSecretKey');

Java

import org.apache.commons.codec.digest.DigestUtils;
import org.apache.commons.codec.digest.HmacUtils;
String sha1HttpString = DigestUtils.sha1Hex("ExampleHttpString");
String signKey = HmacUtils.hmacSha1Hex("YourSecretKey", "ExampleKeyTime");

Python

import hmac
import hashlib
sha1_http_string = hashlib.sha1('ExampleHttpString'.encode('utf-8')).hexdigest()
sign_key = hmac.new('YourSecretKey'.encode('utf-8'), 'ExampleKeyTime'.encode('utf-8'), hashlib.sha1).hexdigest()

Node.js

var crypto = require('crypto');
var sha1HttpString = crypto.createHash('sha1').update('ExampleHttpString').digest('hex');
var signKey = crypto.createHmac('sha1', 'YourSecretKey').update('ExampleKeyTime').digest('hex');

Go

import (
"crypto/hmac"
"crypto/sha1"
)
h := sha1.New()
h.Write([]byte("ExampleHttpString"))
sha1HttpString := h.Sum(nil)
var hashFunc = sha1.New
h = hmac.New(hashFunc, []byte("YourSecretKey"))
h.Write([]byte("ExampleKeyTime"))
signKey := h.Sum(nil)

Examples

Preparations

Log in to the CAM console and go to the Manage API Key page to obtain your APPID, SecretId, and SecretKey. Below is an example:

APPID	SecretId	SecretKey
1250000000	AKIDQjz3ltompVjBni5LitkWHFlFpwkn9U5q	BQYIM75p8x0iWVFSIgqEKwFprpRSVHlz

Uploading an object

Original request

PUT /exampleobject(%E8%85%BE%E8%AE%AF%E4%BA%91) HTTP/1.1
Date: Thu, 16 May 2019 06:45:51 GMT
Host: examplebucket-1250000000.cos.ap-beijing.myqcloud.com
Content-Type: text/plain
Content-Length: 13
Content-MD5: mQ/fVh815F3k6TAUm8m0eg==
x-cos-acl: private
x-cos-grant-read: uin="100000000011"
ObjectContent

Intermediate variables

• KeyTime = 1557989151;1557996351
• SignKey = eb2519b498b02ac213cb1f3d1a3d27a3b3c9bc5f
• UrlParamList = (empty string)
• HttpParameters = (empty string)
• HeaderList = content-length;content-md5;content-type;date;host;x-cos-acl;x-cos-grant-read
• HttpHeaders = content-length=13&content-md5=mQ%2FfVh815F3k6TAUm8m0eg%3D%3D&content-type=text%2Fplain&date=Thu%2C%2016%20May%202019%2006%3A45%3A51%20GMT&host=examplebucket-1250000000.cos.ap-beijing.myqcloud.com&x-cos-acl=private&x-cos-grant-read=uin%3D%22100000000011%22
• HttpString = put\n/exampleobject(tencentcloud)\n\ncontent-length=13&content-md5=mQ%2FfVh815F3k6TAUm8m0eg%3D%3D&content-type=text%2Fplain&date=Thu%2C%2016%20May%202019%2006%3A45%3A51%20GMT&host=examplebucket-1250000000.cos.ap-beijing.myqcloud.com&x-cos-acl=private&x-cos-grant-read=uin%3D%22100000000011%22\n
• StringToSign = sha1\n1557989151;1557996351\n8b2751e77f43a0995d6e9eb9477f4b685cca4172\n
• Signature = 3b8851a11a569213c17ba8fa7dcf2abec6935172

Here, (empty string) is a zero-byte string and \n is a line break.

Signed request

PUT /exampleobject(%E8%85%BE%E8%AE%AF%E4%BA%91) HTTP/1.1
Date: Thu, 16 May 2019 06:45:51 GMT
Host: examplebucket-1250000000.cos.ap-beijing.myqcloud.com
Content-Type: text/plain
Content-Length: 13
Content-MD5: mQ/fVh815F3k6TAUm8m0eg==
x-cos-acl: private
x-cos-grant-read: uin="100000000011"
Authorization: q-sign-algorithm=sha1&q-ak=AKIDQjz3ltompVjBni5LitkWHFlFpwkn9U5q&q-sign-time=1557989151;1557996351&q-key-time=1557989151;1557996351&q-header-list=content-length;content-md5;content-type;date;host;x-cos-acl;x-cos-grant-read&q-url-param-list=&q-signature=3b8851a11a569213c17ba8fa7dcf2abec6935172
ObjectContent

Downloading an object

Original request

GET /exampleobject(%E8%85%BE%E8%AE%AF%E4%BA%91)?response-content-type=application%2Foctet-stream&response-cache-control=max-age%3D600 HTTP/1.1
Date: Thu, 16 May 2019 06:55:53 GMT
Host: examplebucket-1250000000.cos.ap-beijing.myqcloud.com

Intermediate variables

• KeyTime = 1557989753;1557996953
• SignKey = 937914bf490e9e8c189836aad2052e4feeb35eaf
• UrlParamList = response-cache-control;response-content-type
• HttpParameters = response-cache-control=max-age%3D600&response-content-type=application%2Foctet-stream
• HeaderList = date;host
• HttpHeaders = date=Thu%2C%2016%20May%202019%2006%3A55%3A53%20GMT&host=examplebucket-1250000000.cos.ap-beijing.myqcloud.com
• HttpString = get\n/exampleobject(tencentcloud)\nresponse-cache-control=max-age%3D600&response-content-type=application%2Foctet-stream\ndate=Thu%2C%2016%20May%202019%2006%3A55%3A53%20GMT&host=examplebucket-1250000000.cos.ap-beijing.myqcloud.com\n
• StringToSign = sha1\n1557989753;1557996953\n54ecfe22f59d3514fdc764b87a32d8133ea611e6\n
• Signature = 01681b8c9d798a678e43b685a9f1bba0f6c0e012

Here, \n is a line break.

Signed request

GET /exampleobject(%E8%85%BE%E8%AE%AF%E4%BA%91)?response-content-type=application%2Foctet-stream&response-cache-control=max-age%3D600 HTTP/1.1
Date: Thu, 16 May 2019 06:55:53 GMT
Host: examplebucket-1250000000.cos.ap-beijing.myqcloud.com
Authorization: q-sign-algorithm=sha1&q-ak=AKIDQjz3ltompVjBni5LitkWHFlFpwkn9U5q&q-sign-time=1557989753;1557996953&q-key-time=1557989753;1557996953&q-header-list=date;host&q-url-param-list=response-cache-control;response-content-type&q-signature=01681b8c9d798a678e43b685a9f1bba0f6c0e012