Voice Recording Encryption

Today, by default, all Programmable Voice Recordings are encrypted at rest while stored in Twilio's cloud storage. With Voice Recording Encryption enabled, your recordings are encrypted with your public key as soon as the call ends, while the recording is within the Twilio infrastructure, and before it is in cloud storage. The recording remains in this encrypted state until you retrieve it, ensuring that the recording can only be accessed by you, the holder of the corresponding private key.

The Voice Recording Encryption feature is implemented using hybrid encryption. The following are the summarized set of steps of encryption/decryption for each recording.

1. Twilio generates a random Content Encryption Key (CEK) for each recording.
2. Twilio encrypts the recording content with the generated CEK using the AES256-GCM cipher.
3. Twilio encrypts the CEK with the customer's public key using the RSAES-OAEP-SHA256-MGF1 cipher.

1. Customer retrieves the CEK and Initial Vector (IV) encryption values for the recording.
2. Customer decrypts the CEK using their private key.
3. Customer decrypts the recording content using the CEK, along with the IV encryption value.

Detailed decryption steps and code samples can be found later in this guide.

First, generate an RSA public/private key pair. There are many different ways to do this, we recommend using openssl. Once you have openssl installed, you can generate a 2048 length private key with this command:

openssl genrsa -out private_key.pem 2048

The generated file, private_key.pem, contains your private key, which will look something like this:

1
-----BEGIN RSA PRIVATE KEY-----
2
MIIEpAIBAAKCAQEAtePBUk3IM45Jj8eFFrmwzjr/2seEtMknl5OD7VDBipazsq5v
3
MBnIYcE+EuzDiFC5XXww9rncFRZC0I3hLUejUTkJNZjMDQzVFkGXo9+A4MsXRZqK
4
OOYhCNAr2C1acpHKK6bEqGhRW2F2R0dSndbEKOCpPKD70ZF2aZyQdb//9104ROdh
5
bvsycQD7ZGQ8V5SoUo6kPBjQv1sbi99LN6uQm+trUDHkBhbpeKU836YPpIH1ZAqG
6
h2sSzRHN0eXdOPYNdu649ZuOSz0kIUN22e8R39suRhu6VbrC2kvVz2Su+tSPMWlp
7
gKjMboVKrsWUH9B1fQM9ajixc8fc892ZoGBqaQIDAQABAoIBAQCd5BlbEr4pUui0
8
cOQs+ABs5XZYOj4OmVdPEvTAuwtm/K78+sL2JEt34EG8N978o+ZlKntukaRkgbB6
9
Tc8ceUViKnq+Fed7pJoM+d9il4/Okz2eZCp8ffhLKDoHLEeJkNjIz7mC3xtQkegU
10
s+sZrOcW/P6r7KrsHrOFti0IqiTOWps1M6gIUKFWcIRIh/6SyN0gmdDxmfGD9o4W
11
CePswAS0fmwMZPCwQ9GazC8iVL+CvrF92UNfmNQSUiuR0GynOlsMnDu2GvSim3yO
12
9lqWAo1yyEBVU8x6pS1wFTdsXQ7Ch2Ei9ZU+XE6SL5lq3jSc8WqIGmLvZ+zw5eAR
13
8J73+fkBAoGBAO12zPHKgvN5nHRTrO3gNVcl92201umLHllf2elOjlE98/qtNsuX
14
R96LILDv4rgSjwH0+eVQW2g2B5o3D6KPvXdEvUmaRIXDValqr1UzED1DFWLs1MQK
15
HO30rJSpfWpTD3B56zvMb620avIBv3+Oe6kmjImn7Db/nyuEZrs49sE5AoGBAMQW
16
bAXgbG5GDUMVvJfrWwiXz3Ip7yv2j6xz5MtU58gytVV2ZnesLSCfpKrUpalPDWsX
17
04ZBuZ7bqZR4UpGQnGlYePtttKMdI4Vbo+tPK8gNN8ELu+8Fgmr0UNv3BWmcSRzo
18
AfiWWIHZS6iAkPoaYWQtCtf3WU0wnt/beiP/NWKxAoGAafCUYlLMtT7OE/+4qK9c
19
XLLtfh4tuyd7tLfUigen6orPLEjWp2GoiJpdTVLYPPLapi7axflhrk5ceeqSqR2j
20
k3AxWoLeiyaoMtsLueD8H7ir8+Rgz80LNwXvcKtk7mh7/NwHnDgKot5Yz/sDqi6w
21
8Lfn/wnRkn/cTRfWlTRGsdECgYEAuXjP4lsdlMyT3MFhqnzGlYEqibyaaoYD7cWN
22
Qrpjplw4YsbkMwvbf4EhOyh6LYQFmCdoPxRJ47W4WCPbTa5wE8DIZmGlO6fjIk/E
23
41z2d3nxI5rav0IB0vKWzQiAyR03lqzouF5VBzUmuBIrjzWGqz9jg1WF1VpI3Er3
24
47aQo3ECgYBQ7UZ3IP1+unprNsvVDT4CbjsoAypstmQhfgxYiNPY0wB7rvTOWT3q
25
3vwOBwVBjfvkG8yYglYgHc0xGOrqL6DxhMUFTxBe0iDvBX0QM1tpp4apsKdHvuuQ
26
h1icaQZp8WKxBOzVilj3DLoHJEyIrsWWMnDHazV4fxbxijpj4uwJCw==
27
-----END RSA PRIVATE KEY-----

1
openssl pkcs8 -in private_key.pem -topk8 -nocrypt -out private_key_pkcs8.pem
2

You can obtain the public key by executing the following command:

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

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

1
-----BEGIN PUBLIC KEY-----
2
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAtePBUk3IM45Jj8eFFrmw
3
zjr/2seEtMknl5OD7VDBipazsq5vMBnIYcE+EuzDiFC5XXww9rncFRZC0I3hLUej
4
UTkJNZjMDQzVFkGXo9+A4MsXRZqKOOYhCNAr2C1acpHKK6bEqGhRW2F2R0dSndbE
5
KOCpPKD70ZF2aZyQdb//9104ROdhbvsycQD7ZGQ8V5SoUo6kPBjQv1sbi99LN6uQ
6
m+trUDHkBhbpeKU836YPpIH1ZAqGh2sSzRHN0eXdOPYNdu649ZuOSz0kIUN22e8R
7
39suRhu6VbrC2kvVz2Su+tSPMWlpgKjMboVKrsWUH9B1fQM9ajixc8fc892ZoGBq
8
aQIDAQAB
9
-----END PUBLIC KEY-----

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

After you have the RSA public key, 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.

Turn on Voice Recording encryption at a project or subaccount level and select the public key you created in step 2. For the procedure, see Turn on Voice Recording encryption.

After you save your settings, Twilio encrypts all new Recordings on this account with the configured public key.

Obtain the public_key_sid, encrypted_cek, and iv parameters within EncryptionDetails JSON object, which you can retrieved by making an HTTP GET request to the Recordings resource. The EncryptionDetails data will also be posted to your RecordingStatusCallback.

EncryptionDetails includes relevant encryption details if the recording was encrypted with the Voice Recording Encryption feature. It will be null if the recording was not encrypted. The parameters within EncryptionDetails include :

Any recording encrypted with Voice Recording Encryption will contain additional encryption properties on the recording resource. See the request/response example below to query the recording resource metadata.

The request:

curl -X GET 'https://api.twilio.com/2010-04-01/Accounts/ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/Recordings/REXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.json'

The response:

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{
2
  "account_sid": "ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
3
  "api_version": "2010-04-01",
4
  "call_sid": "CAXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
5
  "conference_sid": "CFXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
6
  "channels": 1,
7
  "date_created": "Fri, 14 Oct 2016 21:56:34 +0000",
8
  "date_updated": "Fri, 14 Oct 2016 21:56:38 +0000",
9
  "start_time": "Fri, 14 Oct 2016 21:56:34 +0000",
10
  "price": "-0.0025",
11
  "price_unit": "USD",
12
  "duration": "4",
13
  "sid": "REXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
14
  "source": "StartConferenceRecordingAPI",
15
  "status": "completed",
16
  "error_code": null,
17
  "uri": "/2010-04-01/Accounts/ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/Recordings/REXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.json",
18
  "subresource_uris": {
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    "add_on_results": "/2010-04-01/Accounts/ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/Recordings/REXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/AddOnResults.json",
20
    "transcriptions": "/2010-04-01/Accounts/ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/Recordings/REXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX/Transcriptions.json"
21
  },
22
  "encryption_details": {
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    "type": "rsa-aes",
24
    "encryption_public_key_sid": "CRXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
25
    "encryption_cek": "OV4h6zrsxMIW7h0Zfqwfn6TI2GCNl54KALlg8wn8YB8KYZhXt6HlgvBWAmQTlfYVeLWydMiCewY0YkDDT1xmNe5huEo9vjuKBS5OmYK4CZkSx1NVv3XOGrZHpd2Pl/5WJHVhUK//AUO87uh5qnUP2E0KoLh1nyCLeGcEkXU0RfpPn/6nxjof/n6m6OzZOyeIRK4Oed5+rEtjqFDfqT0EVKjs6JAxv+f0DCc1xYRHl2yV8bahUPVKs+bHYdy4PVszFKa76M/Uae4jFA9Lv233JqWcxj+K2UoghuGhAFbV/JQIIswY2CBYI8JlVSifSqNEl9vvsTJ8bkVMm3MKbG2P7Q==",
26
    "iv": "8I2hhNIYNTrwxfHk"
27
  }
28
}

RecordingStatusCallback is the reliable way to receive webhooks for completed or failed recordings. See this RecordingStatusCallback support article for more details.

Subscribe to 'failed' RecordingStatusCallbackEvent to receive callbacks in recording encryption failure scenarios; these are described later in this article.

Here is an example of a RecordingStatusCallback webhook with encryption parameters:

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"RecordingSource": "OutboundAPI"
2
"EncryptionDetails": "{"type":"rsa-aes","public_key_sid":"CR201607f4ca45a533cdca8d9a828c2a87","encrypted_cek":"ZriXxBEXSywEohXQZV53KGvyzAO1HpKRxCuMo/pcKiT7C+bWKfelZuX0eW1jb7iGcESrOqwvLo4v4GVRPDdJKsaO6R/AVTDcA+he5syPDBgg20ECilAhC/9/CNxfbIuQD+rRKmx0O7SOJJyazbc4zlv+4ClWwDm6g/8z0ekpYs/tNrlQenbxU/Un9uLeeBaJtFKeK5YSUea5n3Kce22iaPZMy3WUGBg+JfOHrccvCjDjX5QQ21I3rcdpgb5nwpzf3MQwmExhW8SJtmQ1cL4jDeKojM255HhhcgOYDwcyrTfY7svUkqNrEKei1q5ZFdBl+SjjKfSdE0BgEvTceZZYrQ==","iv":"7MiadYE7QDgVSRm9"}"
3
"RecordingSid": "REb719a56ceca43b2d06967983570e658a"
4
"RecordingUrl": "https://api.twilio.com/2010-04-01/Accounts/AC18d5c6f2003e8710de63b2f9c412b145/Recordings/REb719a56ceca43b2d06967983570e658a"
5
"RecordingStatus": "completed"
6
"RecordingChannels": "1"
7
"ErrorCode": "0"
8
"CallSid": "CA5987df4d600665d67f53e1bd4cec76d6"
9
"RecordingStartTime": "Tue, 28 May 2019 02:18:02 +0000"
10
"AccountSid": "AC18d5c6f2003e8710de63b2f9c412b145"
11
"RecordingDuration": "5"

1. Retrieve customer private key corresponding to public_key_sid and use it to decrypt the base64-encoded encrypted_cek from your retrieved EncryptionDetails object.
2. Use the decrypted CEK and the base 64-encoded iv from your retrieved EncryptionDetails object to initialize an AES256-GCM SecretKey object.
3. Decrypt the encrypted recording using the SecretKey.

To help you with your own code, here are some decryption code samples in key languages:

• Java

  • Note: Your private key must be in PKCS8 format for this tool.

• JavaScript

  • Note: Your private key must be in PKCS8 format for this tool.

• Python

• C#

Voice Recording Encryption is enabled but Twilio is unable to determine or retrieve the public key configured for recording encryption

• The account's most recently added retrievable public key, if one exists, will be used for encryption.
• The public_key_sid within EncryptionDetails will represent the SID of the public key used for encryption, which is not necessarily the one added to the account.
• A notification will be sent to the account. The notification is viewable from the Debugger in the Console. It indicates that an alternative public key was used.

Twilio is unable to encrypt the recording because there aren't any public keys on the account or an intermittent system issue occurred.

• The recording file is deleted and will not be available for access.
• Recording resource metadata will have a Status of failed, an ErrorCode of 16104, and an EncryptionDetails that is null.
• A RecordingStatusCallback will be sent, if configured via RecordingStatusCallbackEvent, with a Status of failed, and an ErrorCode of 16104. EncryptionDetails is not included in the callback.
• A notification will be sent to the account. The notification is viewable from the Debugger in the Console. It indicates a failure was due to inaccessibility of public keys or an internal system error.

• Voice Recording settings
• CredentialPublicKey Resource
• Twilio REST API - Recording Resource
• TwiML - Record
• TwiML - Dial
• TwiML - Conference
• Twilio Voice - Making Calls
• GitHub - Encrypted Media Recordings Tools