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https://github.com/nginx-modules/ngx_http_hmac_secure_link_module

HMAC Secure Link module for NGINX.
https://github.com/nginx-modules/ngx_http_hmac_secure_link_module

authentication blake2 expiration-period gost hash hashing-algorithm hmac iso-8601 legacy lifetime module nginx openssl rfc-2104 security sha3 sha512 sm3 timestamp unix-timestamp

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HMAC Secure Link module for NGINX.

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README 

        
Nginx HMAC Secure Link Module

=============================



Description:

============



The Nginx HMAC secure link module enhances the security and functionality of the standard secure link module.  

Secure token is created using secure HMAC construction with an arbitrary hash algorithm supported by OpenSSL, e.g.:

`blake2b512`, `blake2s256`, `gost`, `md4`, `md5`, `mdc2`, `rmd160`, `sha1`, `sha224`, `sha256`,

`sha3-224`, `sha3-256`, `sha3-384`, `sha3-512`, `sha384`, `sha512`, `sha512-224`, `sha512-256`, `shake128`, `shake256`, `sm3`.



Furthermore, secure token is created as described in RFC2104, that is,

`H(secret_key XOR opad,H(secret_key XOR ipad, message))` instead of a simple `MD5(secret_key,message, expire)`.



Installation:

=============



You'll need to re-compile Nginx from source to include this module.  

Modify your compile of Nginx by adding the following directive (modified to suit your path of course):



Static module (built-in nginx binary)



    ./configure --add-module=/absolute/path/to/ngx_http_hmac_secure_link_module



Dynamic nginx module `ngx_http_hmac_secure_link_module.so` module



    ./configure --with-compat --add-dynamic-module=/absolute/path/to/ngx_http_hmac_secure_link_module



Build Nginx



    make

    make install



Usage:

======



Message to be hashed is defined by `secure_link_hmac_message`, `secret_key` is given by `secure_link_hmac_secret`, and hashing algorithm H is defined by `secure_link_hmac_algorithm`.



For improved security the timestamp in ISO 8601 the format `2017-12-08T07:54:59+00:00` (one possibility according to ISO 8601) or as `Unix Timestamp` should be appended to the message to be hashed.



It is possible to create links with limited lifetime. This is defined by an optional parameter. If the expiration period is zero or it is not specified, a link has the unlimited lifetime.



Configuration example for server side.



```nginx

location ^~ /files/ {

    # Variable to be passed are secure token, timestamp, expiration period (optional)

    secure_link_hmac "$arg_st,$arg_ts,$arg_e";



    # Secret key

    secure_link_hmac_secret "my_secret_key";



    # Message to be verified

    secure_link_hmac_message "$uri|$arg_ts|$arg_e";



    # Cryptographic hash function to be used

    secure_link_hmac_algorithm sha256;



    # In production environment, we should not reveal to potential attacker

    # why hmac authentication has failed

    # - If the hash is incorrect then $secure_link_hmac is a NULL string.

    # - If the hash is correct but the link has already expired then $secure_link_hmac is "0".

    # - If the hash is correct and the link has not expired then $secure_link_hmac is "1".

    if ($secure_link_hmac != "1") {

        return 404;

    }



    rewrite ^/files/(.*)$ /files/$1 break;

}

```



Application side should use a standard hash_hmac function to generate hash, which then needs to be base64url encoded. Example in Perl below.



#### Variable $data contains secure token, timestamp in ISO 8601 format, and expiration period in seconds



```nginx

perl_set $secure_token '

    sub {

        use Digest::SHA qw(hmac_sha256_base64);

        use POSIX qw(strftime);



        my $now = time();

        my $key = "my_very_secret_key";

        my $expire = 60;

        my $tz = strftime("%z", localtime($now));

        $tz =~ s/(\d{2})(\d{2})/$1:$2/;

        my $timestamp = strftime("%Y-%m-%dT%H:%M:%S", localtime($now)) . $tz;

        my $r = shift;

        my $data = $r->uri;

        my $digest = hmac_sha256_base64($data . "|" . $timestamp . "|" . $expire,  $key);

        $digest =~ tr(+/)(-_);

        $data = "st=" . $digest . "&ts=" . $timestamp . "&e=" . $expire;

        return $data;

    }

';

```



A similar function in PHP



```php

$secret = 'my_very_secret_key';

$expire = 60;

$algo = 'sha256';

$timestamp = date('c');

$unixtimestamp = time();

$stringtosign = "/files/top_secret.pdf|{$unixtimestamp}|{$expire}";

$hashmac = base64_encode(hash_hmac($algo, $stringtosign, $secret, true));

$hashmac = strtr($hashmac, '+/', '-_');

$hashmac = str_replace('=', '', $hashmac);

$host = $_SERVER['HTTP_HOST'];

$loc = "https://{$host}/files/top_secret.pdf?st={$hashmac}&ts={$unixtimestamp}&e={$expire}";

```



Using Unix timestamp in Node.js



```javascript

const crypto = require("crypto");

const secret = 'my_very_secret_key';

const expire = 60;

const unixTimestamp = Math.round(Date.now() / 1000.);

const stringToSign = `/files/top_secret.pdf|${unixTimestamp}|${expire}`;

const hashmac = crypto.createHmac('sha256', secret).update(stringToSign).digest('base64')

      .replace(/=/g, '')

      .replace(/\+/g, '-')

      .replace(/\//g, '_');

const loc = `https://host/files/top_secret.pdf?st=${hashmac}&ts=${unixTimestamp}&e=${expire}`;

```



Bash version



```shell

#!/bin/bash



SECRET="my_super_secret"

TIME_STAMP="$(date -d "today + 0 minutes" +%s)";

EXPIRES="3600"; # seconds

URL="/file/my_secret_file.txt"

ST="$URL|$TIME_STAMP|$EXPIRES"

TOKEN="$(echo -n $ST | openssl dgst -sha256 -hmac $SECRET -binary | openssl base64 | tr +/ -_ | tr -d =)"



echo "http://127.0.0.1$URL?st=$TOKEN&ts=$TIME_STAMP&e=$EXPIRES"

```



It is also possible to use this module with a Nginx acting as proxy server.



The string to be signed is defined in `secure_link_hmac_message`, the `secure_link_hmac_token` variable contains then a secure token to be passed to backend server.



```nginx

location ^~ /backend_location/ {

    set $expire 60;



    secure_link_hmac_message "$uri|$time_iso8601|$expire";

    secure_link_hmac_secret "my_very_secret_key";

    secure_link_hmac_algorithm sha256;



    proxy_pass "http://backend_server$uri?st=$secure_link_hmac_token&ts=$time_iso8601&e=$expire";

}

```



Embedded Variables

==================

* `$secure_link_hmac` -

* `$secure_link_hmac_token` -

* `$secure_link_hmac_expires` - The lifetime of a link passed in a request.



Contributing:

=============



Git source repositories: http://github.com/nginx-modules/ngx_http_hmac_secure_link_module/tree/master



Please feel free to fork the project at GitHub and submit pull requests or patches.