Amazon Elastic Transcoder
Developer Guide (API Version 2012-09-25)

Using Client-side Encryption with Elastic Transcoder

With Elastic Transcoder, you can transcode files that you encrypted and uploaded to Amazon S3. In this tutorial, we show you how to encrypt your file, set up Elastic Transcoder to transcode an encrypted file, and create a job to transcode the file. This tutorial assumes that you are using Linux.

Elastic Transcoder supports three encryption algorithms. This tutorial uses AES-CBC-PKCS7 (AES CBC 128-bit with padding) because it's natively supported by OpenSSL. OpenSSL 1.0.1 and later also support AES-CTR.

Note

You can't use Elastic Transcoder with the AWS Encryption SDK (or CLI) because the SDK does not show the initialization vector. Elastic Transcoder needs the initialization vector to transcode an encrypted file.

Prerequisites

To encrypt and transcode a file, you need the following:

  • A video or audio file that you want to encrypt and transcode.

    For this tutorial, we use an input video called input.mp4.

  • A KMS master key ARN.

    For this tutorial, we refer to this as YourKmsKeyArnHere.

  • A plaintext key. This is a string of characters. It can be 16, 24, or 32 characters long.

    For this tutorial, we use the 16-byte string keykeykeykeykeyk.

  • An initialization vector. This is a string of 16 characters.

    For this tutorial, we use the initialization vector 1234567890123456.

Step 1: Convert Your Plaintext Key and Initialization Vector

To encrypt a file and transcode the encrypted file, you need the base64 and hexadecimal versions of your plaintext key and initialization vector. Start by converting your plaintext key and initialization vector into base64 and hexadecimal. To do that, run the following commands on the command line:

echo -n "keykeykeykeykeyk" | base64 echo -n "1234567890123456" | base64 echo -n "keykeykeykeykeyk" | xxd -p echo -n "1234567890123456" | xxd -p

Note

Make sure to include the -n option when running the echo commands. This tells Linux to encode only the given string, and to not include a newline character at the end of the string. If you forget the -n, the encoded results include extra characters.

Record the results. For this example, the results are the following:

a2V5a2V5a2V5a2V5a2V5aw== MTIzNDU2Nzg5MDEyMzQ1Ng== 6b65796b65796b65796b65796b65796b 31323334353637383930313233343536

Step 2: Encrypt Your Input File

Now that you encoded the input key and initialization vector, encrypt your input file with the hexadecimal input key and initialization vector. To encrypt your file, run the following command:

openssl enc -nosalt -aes-128-cbc -in "input.mp4" -out "encrypted.mp4" -K "6b65796b65796b65796b65796b65796b" -iv "31323334353637383930313233343536"

Step 3: Encrypt Your Plaintext Key With KMS

Now that you have an encrypted file, encrypt your KMS key. KMS supports only the Galois/Counter Mode (GCM) encryption algorithm, so your key is encrypted with GCM no matter which encryption algorithm you used for your input file.

Make sure that you call the same region for KMS that your KMS key is actually in. The region is visible in your master key ARN, and looks like us-east-1. You can use --region in your CLI call to specify the correct region. Also, make sure that you include the parameter --encryption-context "service=elastictranscoder.amazonaws.com". If you don't include it, the call to KMS succeeds, but Elastic Transcoder won't be able to decrypt your file. Each time you call the encryption operation it returns a different result, even if you use the same plaintext key.

Run the following command to encrypt your KMS key:

aws kms encrypt --key-id "YourKmsKeyArnHere" --encryption-context "service=elastictranscoder.amazonaws.com" --plaintext "a2V5a2V5a2V5a2V5a2V5aw==" | jq -r ".CiphertextBlob"

Your result is a blob of ciphertext that looks like this:

CiCCgQY/OrQ5/gdcoup5mIrqT/WTIjxM6ZSge+uRZ7tiAhKXAQEBAgB4goEGPzq0Of4HXKLqeZiK6k/1kyI8TOmUoHvrkWe7YgIAAABuMGwGCSqGSIb3DQEHBqBfMF0CAQAwWAYJKoZIhvcNAQcBMB4GCWCGSAFlAwQBLjARBAxIEi6/cfLGY+6ia0UCARCAK5wHYxg+3oHCzX4B4RqUY9N+YmVRooWmncNN4NKduc6jA/m+A+cKAFSvuF0=

Step 4: Generate the Ciphertext MD5 Hash

Now that you have an encrypted file and an encrypted KMS key, use the encrypted KMS key to generate a ciphertext hash:

echo -n "CiCCgQY/OrQ5/gdcoup5mIrqT/WTIjxM6ZSge+uRZ7tiAhKXAQEBAgB4goEGPzq0Of4HXKLqeZiK6k/1kyI8TOmUoHvrkWe7YgIAAABuMGwGCSqGSIb3DQEHBqBfMF0CAQAwWAYJKoZIhvcNAQcBMB4GCWCGSAFlAwQBLjARBAxIEi6/cfLGY+6ia0UCARCAK5wHYxg+3oHCzX4B4RqUY9N+YmVRooWmncNN4NKduc6jA/m+A+cKAFSvuF0=" | base64 -d | md5sum -b | cut -f 1 -d " " | xxd -r -p | base64

Your result looks like this:

zG9MId7htnmIZEWCXXG5yg==

Save this MD5 hash for Step 7: Create Your Elastic Transcoder Job.

Step 5: Upload Your Encrypted File

Upload encrypted.mp4 to the S3 bucket that you want to use as your input bucket.

To upload your encrypted file to Amazon S3

  1. Sign in to the AWS Management Console and open the Amazon S3 console at https://console.aws.amazon.com/s3/.

  2. In the list of buckets, choose the name of your input bucket.

  3. Choose Upload.

  4. In the Upload dialog box, choose Add Files, and choose the file that you want to upload.

  5. Choose Upload.

Step 6: Configure Your Elastic Transcoder Pipeline

Now that you have an encrypted KMS master key and an encrypted file, configure your pipeline to use your KMS master key.

Check that your pipeline has the correct AWS KMS Key ARN configured. If it doesn't, you can update your pipeline to add or edit that field.

To configure your pipeline with your KMS key

  1. Sign in to the AWS Management Console and open the Elastic Transcoder console at https://console.aws.amazon.com/elastictranscoder/.

  2. Either choose Create New Pipeline or select your pipeline and choose Edit.

  3. Scroll down to the Encryption (Optional) section, and expand it if necessary.

  4. For AWS KMS Key ARN, choose Custom. In the text area, paste the ARN of your KMS master key. In this tutorial, the KMS master key ARN is YourKmsKeyArnHere.

  5. If you're editing an existing pipeline, choose Save. If you're creating a pipeline, choose Create Pipeline.

Step 7: Create Your Elastic Transcoder Job

Now that you have your encrypted file, your encrypted KMS master key, and an Elastic Transcoder pipeline, you can transcode your encrypted file by creating a job. For this example, use the following command to create a job with the Elastic Transcoder API:

aws elastictranscoder create-job --pipeline-id "YourPipelineIdHere" --inputs '[{"Key":"encrypted.mp4","Encryption":{"Mode":"aes-cbc-pkcs7","Key":"CiCCgQY/OrQ5/gdcoup5mIrqT/WTIjxM6ZSge+uRZ7tiAhKXAQEBAgB4goEGPzq0Of4HXKLqeZiK6k/1kyI8TOmUoHvrkWe7YgIAAABuMGwGCSqGSIb3DQEHBqBfMF0CAQAwWAYJKoZIhvcNAQcBMB4GCWCGSAFlAwQBLjARBAxIEi6/cfLGY+6ia0UCARCAK5wHYxg+3oHCzX4B4RqUY9N+YmVRooWmncNN4NKduc6jA/m+A+cKAFSvuF0=","KeyMd5":"zG9MId7htnmIZEWCXXG5yg==","InitializationVector":"MTIzNDU2Nzg5MDEyMzQ1Ng=="}}]' --outputs '[{"Key":"output.mp4","PresetId":"YourPresetIdHere"}]'

Note

The transcoded output file that is generated from this example isn't encrypted. If you want to create a job that generates an encrypted output, specify encryption parameters for the output instead of for (or in addition to) the input.

You now have a pipeline set up to transcode the files that you encrypt with your KMS key.