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Encrypting your Stored Media


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This page is for reference only. We are no longer onboarding new customers to Programmable Video. Existing customers can continue to use the product until December 5, 2024(link takes you to an external page).
We recommend migrating your application to the API provided by our preferred video partner, Zoom. We've prepared this migration guide(link takes you to an external page) to assist you in minimizing any service disruption.

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Overview

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This guide explains how to encrypt Twilio Video Recordings and Compositions.

Note: Once you activate encryption, only you will be able to decipher. No one at Twilio --including Twilio support-- will be able to decrypt your content.

Use this feature when you need to ensure that your recorded media is encrypted end-to-end, and you are willing to accept the additional work of decrypting and post-processing your audio/video recordings yourself.



Encrypted Recordings Vs Encrypted Compositions

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Video Recordings and Video Compositions have separated encryption settings. This means that encryption can be activated independently on them. However, composing Recordings requires access to their raw media. As a result:

If you encrypt your Recordings, you will not be able to compose them.

If you need to compose your Recordings, you must store them unencrypted. However, those Recordings are only needed temporarily: as soon as the Composition is created they can be deleted permanently and irrevocably using Twilio's Video Recordings API.


Twilio Video uses the standard WebRTC security architecture(link takes you to an external page) to guarantee that the live audio/video communication is cryptographically protected point-to-point.

When you enable Recording in your Group Rooms, audio/video is decrypted in memory before being stored securely in Twilio's cloud. Once stored, you can only access the decrypted recordings using your Twilio account credentials (your Account SID/Token or an API Key/API Key Secret).

When you enable encryption in your Video Recordings or Compositions, Twilio adds an additional layer of security: All the media files are encrypted as they are written to disk using the AES 256-bit symmetric encryption algorithm. Once encrypted, only a user who has the private key can decrypt the recordings.

Programmable Video uses an encryption mechanism provided by Amazon clients called "envelope encryption". Here is how it works:

  • First, you create a public cryptography key pair. You provide to Twilio the public key, but you keep the private key secret and safe.
  • For each encrypted Recording or Composition, a one-time-use 256-bit envelope symmetric cryptographic key is generated and fed to an AES/CBC/PKCS5Padding cipher that encrypts the envelope payload (i.e the media content), and generates the protected file.
  • The envelope symmetric key is then cyphered itself with the provided public key and stored as part of the envelope. After that, the symmetric key is discarded and cannot be recovered by Twilio never again.

Only a user with the private key can decrypt the media content as the original AES symmetric key cannot be recovered. This mechanism guarantees that unencrypted media files are never persisted, and that Twilio cannot decrypt the envelope once it is generated.


Enabling Encryption in your Twilio account

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Step 1: Generate a RSA key pair

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First, generate an RSA PKCS#1 key pair. There are many different ways to do this, but the simplest one is to use openssl(link takes you to an external page). Once you have openssl installed, you can generate a 2048 length private key with this command:


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openssl genrsa -out private_key.pem 2048

The generated file private_key.pem contains your private key, which should be similar to this:


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$ cat private_key.pem
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-----BEGIN RSA PRIVATE KEY-----
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MIIEpAIBAAKCAQEAtePBUk3IM45Jj8eFFrmwzjr/2seEtMknl5OD7VDBipazsq5v
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.
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.
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.
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h1icaQZp8WKxBOzVilj3DLoHJEyIrsWWMnDHazV4fxbxijpj4uwJCw==
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-----END RSA PRIVATE KEY-----

Note: It is your responsibility to keep your private key safe. If you loose your private key you will never be able to decrypt any of the files stored using on the corresponding public key.

You can obtain the public key executing the following:


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openssl rsa -in private_key.pem -pubout -out public_key.pem

The file public_key.pem contains the public key. It should look like this:


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$ cat public_key.pem
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-----BEGIN PUBLIC KEY-----
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MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAtePBUk3IM45Jj8eFFrmw
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.
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.
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.
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aQIDAQAB
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-----END PUBLIC KEY-----

In the next step, you will configure Twilio with this public key.

Step 2: Create a Twilio Public Key resource

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Once you have the RSA public key, you must create a Twilio Public Key resource that contains your public key. You can do this with the Public Key Resource REST API or, in the Twilio Console in the Runtime Public Keys management page(link takes you to an external page). Press the button Create new Public key:

On the popup that opens, provide a friendly name for your public key. Then, copy the content of the public_key.pem file generated in step 1 and paste it into the PUBLIC KEY field. Press Create to create the Twilio Public Key:

The Twilio Public Key resource has an associated unique SID identifier with the form CRxx. Make note of this Public Key SID because you will need it later:

Step 3: Enabling Encryption in your Account

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Enabling Encrypted Recordings

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You have two options to enable encrypted Recordings:

Enabling Encrypted Recordings using the Twilio's Console

Enabling Encryption using the Recording Settings API

Check the Recording Settings API documentation for detailed information on how to enable programmatically encrypted recordings.

Enabling Encrypted Compositions

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You have two options to enable encrypted Compositions:

Enabling Encrypted Compositions using the Twilio's Console

Enabling Encryption using the Composition Settings API

Check the Composition Settings API documentation for detailed information on how to enable programmatically encrypted compositions.


Decrypting your Recordings and Compositions

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We suggest two decrypting alternatives:

  • Alternative 1 : To use a Java utility program. See step 4 for instructions.
  • Alternative 2 : To do it step by step using command line tools. See step 5 for instructions.

Step 4: Decrypting using a Java utility program

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Here we provide instructions on how to write a Java program performing the decryption.

Step 4.1: Install Java Cryptography Extensions

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If you are using Oracle's JRE, and due to legal restrictions, you need to install separately the JCE (Java Cryptography extensions). For doing so, just download the JCE(link takes you to an external page), uncompress it and follow the instructions provided in the included README.txt file.

Step 4.2: Convert your private key to PKCS #8 format

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JCE requires your private key to be in PKCS #8 format, for converting it, you just need to execute the following:


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openssl pkcs8 -in private_key.pem -topk8 -nocrypt -out private_key_pkcs8.pem

In the above:

  • private_key.pem is the filename of the private key you generated in Step 1.
  • private_key_pkcs8.pem is the filename of your PKCS #8 private key.

Step 4.3: Decrypt using the Java utility program

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The Java decrypting utility can be cloned from this GitHub project(link takes you to an external page). After cloning, execute the following Maven command at its root folder:


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mvn clean package

Once the compilation is completed, do the following:


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java -jar target/twilio-media-decrypter.jar SKxx:API_SECRET SidToDecrypt private_key_pkcs8.pem decrypted-filename

In the above:

  • Replace SKxx with your Twilio API Key SID.
  • Replace SK_SECRET with the corresponding Twilio API Key Secret.
  • Replace SidToDecrypt with the SID of the Recording (e.g. RTXXXX) or Composition (e.g. CJXXXX) you want to decrypt.
  • private_key_pkcs8.pem is the filename of the PKCS #8 key you generated in step 4.2
  • decrypted-filename is the name of the file where you want to store your decrypted media data. You may wish to add the appropriate extension so that your media player recognizes it (e.g. .mkv for video recordings, .mka for audio recordings, .mp4 or .webm for Compositions, etc.)

Remember that this Java utility is provided for tutorial purposes and is not intended to be used in production applications.

Step 5: Decrypting using Command Line Tools

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Step 5.1: Obtain the encrypted media URL

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You can retrieve the media data of a specific Recording or Composition by fetching its /Media subresource. Any request to this resource will return a URL where the corresponding media file can be downloaded, you just need to do the following:

For Recordings


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curl 'https://video.twilio.com/v1/Recordings/RTxx/Media' \
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-u 'SKxx:SK_SECRET'

For Compositions


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curl 'https://video.twilio.com/v1/Compositions/CJxx/Media' \
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-u 'SKxx:SK_SECRET'

In the above:

  • Replace RTxx or CJxx with the corresponding Recording or Composition SID.
  • Replace SKxx with your Twilio API Key SID.
  • Replace SK_SECRET with the corresponding Twilio API Key Secret.

In both cases, as part of the answer to the request you will receive a redirect to a URL with the following structure:

https://documentation-example-twilio-bucket.s3.amazonaws.com/ACxx/RTyy.mkv?X-Amz-Security-Token=zz

We call this the encrypted media URL.

Step 5.2: Download the encrypted file and collect its headers

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Execute the following command replacing:

  • encrypted-media-url with the encrypted media URL obtained in step 5.1 .
  • encrypted-filename with the filename where you want to store the encrypted data.

wget -S encrypted-media-url -O encrypted-filename

When a media file is cryptographically protected, a request to the encrypted media URL returns the encrypted file, along with an initialization vector and the encrypted one-time symmetric master key at the HTTP headers x-amz-meta-x-amz-iv and x-amz-meta-x-amz-key. To obtain both take a look to the output of the command above:


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Resolving documentation-example-twilio-bucket.s3.amazonaws.com... 52.216.64.96
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Connecting to documentation-example-twilio-bucket.s3.amazonaws.com|52.216.64.96|:443... connected.
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HTTP request sent, awaiting response...
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HTTP/1.1 200 OK
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x-amz-id-2: 8x0XN6KDeLuhHLIe8fa58OdD3+xVyNgv2og/gpMOFpSqWc5JGV+aDpc7fJSCS9yGkwRtey+9lk8=
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x-amz-request-id: 5B3FBF0985E71EEC
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Date: Fri, 24 Nov 2017 14:11:30 GMT
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Last-Modified: Thu, 23 Nov 2017 16:47:17 GMT
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ETag: "d9e5869fc33019fc7fb055c0b705e105"
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x-amz-meta-x-amz-key: 0ZY1jiGSu/FlI4l1OnNFeWvWFXUOEQ2apv3/OtMFlwLO83bHlB44gbZe2SW6wOBs8UTsxC7bEnY+Gn2tdzp7ltzrKtBu7cfMzOxshABFiiJbCSBmOzUHs3OkU30Wi3Hq953SJJO+4W0DAINfhGiDlWxgIbjHegamneJ983DDpm+AyKa77jq5T+4LxJdOv5bqU4ioZKetv/OA987JZaetPVTr55uSmqr8SbsX9xmaIKjo7V6ivutwcCKWX9bvf1qxUu/ZohTmouL2MOocojNMMx5ovTX3QXLCGUwx6pOS83zqHNxmFhU2EHENCs5KNYL6GjhOwmoGyeQPS+pe8bPRFg==
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x-amz-meta-x-amz-unencrypted-content-length: 746518
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x-amz-meta-x-amz-matdesc: {}
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x-amz-meta-x-amz-iv: EmKjzVpvXC9rE6DJ00Xv7Q==
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Accept-Ranges: bytes
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Content-Type: application/octet-stream
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Content-Length: 746528
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Server: AmazonS3
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Length: 746528 (729K) [application/octet-stream]
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Saving to: 'encrypted-filename'
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encrypted-filename 100%[=======================================================================>] 729.03K 789KB/s in 0.9s
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2017-11-24 15:11:33 (789 KB/s) - 'encrypted-filename' saved [746528/746528]

As you can see, both headers x-amz-meta-x-amz-key and x-amz-meta-x-amz-iv are provided. Write down their values: you will need them.

Step 5.3: Obtain the AES encryption key and the initialization vector

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The encrypted envelope symmetric key in x-amz-meta-x-amz-key is base64-encoded. We need first to decode it. For it, replace in, the command below, 0ZY1jiGSu ... with the value of the x-amz-meta-x-amz-key obtained in step 5.2


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base64 -D &lt;&lt;< '0ZY1jiGSu ...' >> key.bin.enc

Now, we can decrypt the public key. For this, and assuming the private_key.pem file you created in step 1 is on the local folder, execute:


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openssl rsautl -decrypt -inkey private_key.pem -in key.bin.enc -out key.bin

Now, we need to do the same steps with the initialization vector. Execute the following replacing the value of the x-amz-meta-x-amz-iv you obtained in step 5.2:


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base64 -D &lt;&lt;< 'EmKjzVpvXC9rE6DJ00Xv7Q==' >> iv.bin

Now, the unencrypted AES key and the initialization vector are respectively in the key.bin and iv.bin files in your local folder.

Step 5.4: Decrypt your media files

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Once the previous steps have been completed, you just need to execute the following for decrypting your encrypted file:


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openssl enc -d -aes-256-cbc -in encrypted-filename -out decrypted-filename -K $(hexdump -v -e '/1 "%02X"' < key.bin) -iv $(hexdump -v -e '/1 "%02X"' < iv.bin)

In the above:

  • encrypted-file-name is the name of the file where you stored your encrypted media file in step 5.2
  • decrypted-filename is the name of the file where you want to store your decrypted media data. You may wish to add the appropriate extension so that your media player recognizes it (e.g. .mkv for video recordings, .mka for audio recordings, .mp4 or .webm for Compositions, etc.)

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