In this post, we’ll look at what encryption HLS supports and how to encrypt your videos with ffmpeg.
Encryption is the process of encoding information in such a way that only authorised parties can read it. The encryption process requires some kind of secret (key) together with an encryption algorithm.
There are many different types of encryption algorithms but HLS only supports AES-128. The Advanced Encryption Standard (AES) is an example of a block cipher, which encrypts (and decrypts) data in fixed-size blocks. It’s a symmetric key algorithm, which means that the key that is used to encrypt data is also used to decrypt it. AES-128 uses a key length of 128 bits (16 bytes).
HLS uses AES in cipher block chaining (CBC) mode. This means each block is encrypted using the cipher text of the preceding block, but this gives us a problem: how do we encrypt the first block? There is no block before it! To get around this problem we use what is known as an initialisation vector (IV). In this instance, it’s a 16-byte random value that is used to intialize the encryption process. It doesn’t need to be kept secret for the encryption to be secure.
Before we can encrypt our videos, we need an encryption key. I’m going to use OpenSSL to create the key, which we can do like so:
$ openssl rand 16 > enc.key
This instructs OpenSSL to generate a random 16-byte value, which corresponds to the key length (128 bits).
The next step is to generate an IV. This step is optional. (If no value is provided, the segment sequence number will be used instead.)
$ openssl rand -hex 16 ecd0d06eaf884d8226c33928e87efa33
Make a note of the output as you’ll need it shortly.
To encrypt the video we need to tell ffmpeg what encryption key to use, the URI of the key, and so on. We do this with -hls_key_info_file option passing it the location of a key info file. The file must be in the following format:
Key URI Path to key file IV (optional)
The first line specifies the URI of the key, which will be written to the playlist. The second line is the path to the file containing the encryption key, and the (optional) third line contains the initialisation vector. Here’s an example (
https://hlsbook.net/enc.key enc.key ecd0d06eaf884d8226c33928e87efa33
Now that we have everything we need, run the following command to encrypt the video segments:
ffmpeg -y \ -i sample.mov \ -hls_time 9 \ -hls_key_info_file enc.keyinfo -hls_playlist_type vod \ -hls_segment_filename "fileSequence%d.ts" \ prog_index.m3u8
Take a look at the generated playlist (
prog_index.m3u8). It should look something like this:
#EXTM3U #EXT-X-VERSION:3 #EXT-X-TARGETDURATION:9 #EXT-X-MEDIA-SEQUENCE:0 #EXT-X-PLAYLIST-TYPE:VOD #EXT-X-KEY:METHOD=AES-128,URI="https://hlsbook.net/enc.key",IV=0xecd0d06eaf884d8226c33928e87efa33 #EXTINF:8.33333 fileSequence0.ts #EXTINF:8.33333 fileSequence1.ts #EXTINF:8.33333 fileSequence2.ts #EXTINF:8.33333 fileSequence3.ts #EXTINF:8.33333 fileSequence4.ts #EXTINF:5.66667 fileSequence5.ts #EXT-X-ENDLIST
Note the URI of the encryption key. The player will retrieve the key from this location to decrypt the media segments. To protect the key from eavesdroppers it should be served over HTTPS. You may also want to implement some of authentication mechanism to restrict who has access to the key. If you’re interested, the book goes into some detail about how to achieve this. Click here to buy a copy.
To verify that the segments really are encrypted, try playing them using a media player like QuickTime or VLC. You shouldn’t be able to. Now run the command above without the encryption and then try playing a segment. Notice the difference.
In this instance, all the segments are encrypted with the same key. It can be beneficial to periodically change the encryption keys to minimise the impact if a particular key is exposed. This is known as key rotation, and the amount of time between successive key generations is referred to as the key rotation period.
To enable key rotation, set the
-hls_flags option to
periodic_rekey. When enabled, the key info file will be checked periodically. If the file has changed, segments will then be encrypted with the new encryption key. However, we still need to come up with a way of generating new keys and updating the key info file. Here’s an example of how it could be done:
#!/bin/bash i=2 while true do sleep 15 tmpfile=`mktemp` openssl rand 16 > enc$i.key echo https://hlsbook.net/enc$i.key > $tmpfile echo enc$i.key >> $tmpfile echo `openssl rand -hex 16` >> $tmpfile mv $tmpfile enc.keyinfo let i++ done
The script uses the same values as before for the base URL (for each key) and key info file. It generates a new encryption key every 15 seconds, updating the key info file accordingly. (In practice you would choose a much longer key rotation period.)
To test it, run ffmpeg again but this time enable key rotation. At the same time, open a new terminal and run the script from the same directory. (The script will run forever until you terminate it.) When ffmpeg has finished, terminate the script.
Take a look at the playlist. You should now see a number of different key entries in the playlist. All the segments that follow a key tag (
#EXT-X-KEY) are now encrypted using the key specified by the tag, instead of using one key to encrypt all segments like before.
Even though HLS supports encryption, which provides some sort of content protection, it isn’t a full DRM solution. If that kind of thing interests you then you may want to take a look at Apple’s FairPlay Streaming solution.
Your post is great. I am new to HLS and your site is really helpful.
I have a question. How can I use mediafilesegmenter to encrypt every segment of the file with different key ? Apple docs says such thing is supported but I couldn’t find any help regarding it.
It would be great if you can guide about it, provide command of it.
You can use the
mediafilesegmenter. It takes as an argument a number that specifies how many segments to encrypt before generating a new key. If you want to encrypt every segment with a different key then I guess you will need to set it to 1.
There’s more information in the Security chapter of the book if you are interested.
I am new to HLS AES encryption can i get the example of the above procedure in the book meaning a video file taken and encryption explained in step by step fashion including openssl and ffmpeg
Thanks however for this informative article
Hi Simon, I hope this thread is still active. I’m new to ffmpeg and tried the commands you mentioned to encrypt HLS with an openssl key, and it all worked. But one basic question- how do I direct the all the encrypted HLS chunks to a separate folder? In your script they just end up in the folder where I ran the script, so its a little messy. Many thanks
You can specify a relative or absolute path to the HLS segments. The following example will output the segments in a directory relative to the location where you run the command:
Make sure the directory you are writing the segments to exists. Take a look at the available options for more information.
Hey Simon, great post. I’m trying to implement an auth system so that when I stream a file, encrypted, over RTMP using ffmpeg you can only consume the the stream if they have a valid decryption key. Is this possible? If the decryption key is included in the generated playlist then *anyone* can consume it which isn’t ideal. Any thoughts, on how to achieve this? Ideally, I don’t have to use a crazy proprietary DRM solution with a license server.
Even though the reference to the key is embedded in an HLS playlist, you can protect access to it. I’m going to assume that the key(s) and/or the playlist are served over HTTPS. You can use something like basic authentication, which requires a username and password, or use client certificates and enable TLS client authentication to restrict access. That’s not going to prevent an authorised user from accessing the key, but it will prevent an unauthorised user from doing so. Other than that, you’re going to have to resort to a DRM solution.
Makes sense, thanks 🙂 I bought your book. It’s been very helpful!
Hi Simon- With the help of your book, I have implemented HLS encryption successfully. The HLS encrypted chunks are stored on a protected server, and the embedded HLS player accesses the keys from the path in the playlist.m3u8 file. The keys are located on the same server that embeds the player, and viewers must be authenticated before accessing the player. To prevent just any site from accessing the key path, I have implemented CORS and only allowed the server where the player is embedded to access. Is there a better, more secure way to restrict access to the keys than CORS? Again, the player and the key store folder are both on the same site- both are off of the site root folder. Thanks for any advice you can give me.
Here’s one idea. You could try including some sort of authentication token in the playlist URL, e.g.
/playlist.m3u8?token=ABCDEFG. As the viewer is authenticated, you could tie the token to their identity.
You would then check on the server if the token is valid or not. If it is valid, you could then set a (session) cookie. Any subsequent requests to the server, e.g. for the key(s), will include the
Cookieheader that you can then use to determine if the request is allowed or not.
An alternative approach to using a cookie could be to generate the playlist dynamically and include the token in the path to the encryption key. There’s an example in the book of how to generate a playlist with PHP that you could use as a starting point.
However, as I mentioned in a comment above, it won’t prevent an authorised user from accessing the key.
Thanks for these ideas- will study them.
I have 2 questions here:
1. What do you actually mean by “it won’t prevent an authorised user from accessing the key”? Could you give some examples?
2. Does HLS works on Android and Windows? I mean, does it work in Android and Windows based web browsers i.e. native browser, Chrome, Firefox and etc?
Let’s assume that you run some sort of video website and users can only watch your videos if they are logged in. (How authentication is implemented is not relevant in this example.) If you are authorized to watch a video, you can access the playlist from your browser. If you can view the playlist, you can see the URL of the decryption key. Type that URL into the browser and you can download the key, which means you can decrypt the individual media segments.
Depends what version of Android you are using. Take a look at the supported media formats, specifically the supported network protocols. I’m not a Windows user but in my experience (on Mac and Linux) HLS works fine in modern versions of desktop browsers like Chrome and Firefox.
So if a user who can watch an encrypted videos, has the access to the URL of the decryption key to decrypt all individual segments, why to encrypt it in the first place? Is there are way to deal with it?
I gave an example of why you would still want to encrypt your videos in a previous comment.
You’ll need to use a DRM solution.
How could we use this with segments, not hls, in ffmpeg?
I have a problem that the subtitles are in dvbsub format and hls doesn’t work with this format, when using hls but encryption only works with hls.
Thank you very much
helped a lot ….
Your post is great, but wish to ask a question.
I already have done it to encrypt the hls stream, as you have told and it works fine with ffmpeg.
Now, as the key is exposed, I wish to implement the key rotation using ffmpeg.
I purchased your book today but it shows only how too use mediafilesegmenter and mediastreamsegmenter to make it.
Is ther any way to make this (key rotation) using ffmpeg?
Thank you very much for any help
-hls_flags periodic_rekeyis enabled, the key info file will be checked periodically for changes. If the file has changed, segments will be encrypted with the new key. However, you will have to write a script (or something) to update the file with the new encryption key. I don’t think it’s possible to specify how often the file is checked.
I’ve updated the post to include an example of how to rotate keys using ffmpeg.
Thank you for the great post. I am able to encrypt the video and was able to play the videos using video.js.
when i installed third party video downloader plugins for browsers and downloaded video. It started downloading in mp4 format and it was playing without any keys.
Can you please tell on how to prevent the video from playing even if downloaded using browser plugins
If the plugin thinks the video is MP4, check the MIME type is configured correctly. The
Content-Typeheader for .ts files should be set to
You need to implement some form of authorization to restrict access to the key if you haven’t already (see my previous comment). If you don’t do this then anybody can download the key and decrypt the video segments, which I suspect is what is happening in your case.
great post and easy to understand, thanks.
Currently I’m running a server where videos are streamed as unencrypted HLS and we have authorization to restrict access to distinct users.
Now, my customer wants to switch to encrypted hls cause they think that logged in users might use a plugin in their browser to download the video and locally store it as MP4.
But there are also hls downloaders that claim to be able to download and decrypt encrypted hls videos.
As far as I understood your article encrypted hls has to send the encryption key to the client in one way or another.
I think a browser plugin has the same access to the key as the browser itself.
So my question is: does encrypted hls bring any advantages over non encrypted hls when we have a legitimated user using such a plugin?
Thanks a lot
You are correct about HLS downloaders. Coincidentally, I used one recently to test an encrypted video stream and it downloaded the video and stored it as an MP4. Interestingly, the one I tried didn’t work with the videos on this site.
To answer your question, I would say no. If a user is authenticated and therefore has direct access to the key, then presumably the plugin also has the same access. It may be possible to thwart these kinds of tools but I don’t know enough about how they work.
However, there are legitimate reasons why you would want to encrypt your videos. For example, if you distribute your videos via a CDN. In this scenario, the content is typically distributed globally on servers you have no control over – it depends on the CDN that you use – so it would make sense to encrypt the video segments.
I have implemented the encryption for my ffmpeg stream and it works very well.
I have a question about the detection of a freezed video.
I need to restart the ffmpeg process when the image is froozen.
I am trying a complex filter as:
-filter_complex “select=’not(mod(n,600))’,select=’lt(scene\,0.06)’,showinfo” \
-vsync vfr /var/www/html/hls/live/CAM1/movement/scn_%03d.jpg \
MOVEMENT is the ffmpeg copied and renamed.
The above script works and it generates the jpeg images.
The question is: how to use this to kill the ffmpeg instance?
I apologise if this is not the place to ask such question, but I didn’t find another place.
Thank you very much for your excelent tutorials and the amazing book.
Thank you for the great article. What I’m wondering about is whether it’s possible to use a pass-phrase based key derivation. I’d like to implement a simple use-case where my goal is to protect some of my videos using a password. Is there any kind of built-in support for this scenario, or is the key file approach the only way?
Thank you for your response in advance, regards,
As far as I know, the key file is the only way. You could try enabling HTTP Basic/Digest authentication on the URL of the key. This will prompt the user for a password.
Hello! I’m trying to encrypt an hls video, but I don’t know how to create a key info file. So I’m stuck there. Can you explain me how can I do it? Thank you!
It’s just a plain text file. You can use any text editor to create it.
Thanks. So I’m using the notepad now, but I’m still doing something wrong…This is my key info file “enc.keyinfo” :
The key.file, the file “enc.keyinfo” and my .mp4 video are located in the same folder.
Then, I run this command:
ffmpeg -y \
-i pruebavideo.mp4 \
-hls_time 9 \
-hls_playlist_type vod \
-hls_segment_filename “fileSequence%d.ts” \
But I keep getting the following error:
error opening key info file enc.keyinfo. Could not write header for output file #0 (incorrect codec parameters ?): No such file or directory. Error initializing output stream 0:1 — [aac @ 0000000002f900c0] Qavg: nan Conversion failed!
Any ideas? Thank you in advance!
The second line of your key info file is missing the name of the file that contains the key. It should look like this:
As all of your files are in the same directory, you can omit the directory path and just include the name of the file. There’s an example in the post.
I’m still unable to see the point of this. With the video streaming in the player, users can still download the video (although it will be in parts e.g. ts) using developer tools
Hi Simon, I have been reading you book but have not found a solution for this issue. with video.js I am getting
VIDEOJS: – “ERROR:” – “(CODE:3 MEDIA_ERR_DECODE)” – “The media playback was aborted due to a corruption problem or because the media used features your browser did not support.”
message: “The media playback was aborted due to a corruption problem or because the media used features your browser did not support.”
But the same playlist and files are playing fine with hls.js I was wondering if you could offer any insight on what may be causing this issue.
What version of video.js are you using? How are you encoding your video? If you can share your playlist, that would be helpful.
There have been other comments elsewhere on the site recently regarding issues with the latest version of video.js, so it could be a bug in the version of the player you are using.
I found his article few years back. It helped me a lot. There has been a lot discussion about safety measures. You could send incorrect decryption key – > then player would modify key to be correct. Users had no ability to decrypt stream unless they use your player or modify decryption key.
Great Post. I was trying to achieve dynamic encryption using key rotation method as suggested in the blog. Although it generates the various key files in the transcoding server as suggested in the bash script. But the encryption of the content is happening via 1st generated key only. There could be below reasons:
1. -hls_flags ‘Periodic_rekey’ in ffmpeg suggest that the ffmpeg will periodically check the *.keyinfo file for the changes in the key & IV. But, whats the duration of the periodic check? Its no where defined in the documentation, even in hlsenc.c file its not there.
2. For this periodic_rekey to work, there should be an option of key rotation period, which is not yet accommodated by ffmpeg.
3. Also, whenever we fork an ffmpeg transcoding process it takes all the value in the hard coded way & only at the time of the initiating the process. Even though the file name remains the same for -hls_key_file_info,
It works for me. I’m using version 4.3. What ffmpeg command are you running?
From what I can tell looking at the source code (hlsenc.c), if periodic re-key is enabled, ffmpeg reads the key info file every time it writes a segment.
You can set the key rotation period by specifying how often the script runs. In the example, I generate a new key every 15 seconds. If you want to rotate the keys every 5 minutes, run the script every 300 seconds, and so on.
I am able to encrypt the hls stream but only using AES128.
My question is: can we use ffmpeg to encrypt an HLS stream with AES256 (or AES194)?
No. HLS only supports AES-128.
I was able to encrypt the stream using methods mentioned in the post, expecting that VLC will have problems playing it.
VLC is still able to play the encrypted stream. I even downloaded the stream as mp4.
How can I prevent this from happening? Stream was served over HTTP.