SOPS: Secrets OPerationS

This is the Python version of SOPS that is no longer maintained. We fix the occasional bug, but all improvements happen in the Go version of SOPS, over in the Master branch. You have been warned!

sop is an editor of encrypted files that supports YAML, JSON and BINARY formats and encrypts with AWS KMS and PGP (via GnuPG). Watch the demo.

Questions? ping "ulfr" in #security on irc.mozilla.org (use a web client like mibbit ).

Installation

• RHEL family:

  sudo yum install gcc git libffi-devel libyaml-devel make openssl openssl-devel python-devel python-pip
  sudo pip install --upgrade sops
  

• Debian family:

  sudo apt-get install gcc git libffi-dev libssl-dev libyaml-dev make openssl python-dev python-pip
  sudo pip install --upgrade sops
  

• MacOS Brew Install:

  brew install sops
  

• MacOS Manual Install:

  brew install libffi libyaml python [1]
  pip install sops
  

In a virtualenv

Assuming you already have libffi and libyaml installed, the following commands will install sops in a virtualenv:

$ sudo pip install virtualenv --upgrade
$ virtualenv ~/sopsvenv
$ source ~/sopsvenv/bin/activate
$ pip install -U sops
$ sops -v
sops 1.9

Test with the dev PGP key

Clone the repository, load the test PGP key and open the test files:

$ git clone https://github.com/mozilla/sops.git
$ cd sops
$ gpg --import tests/sops_functional_tests_key.asc
$ sops example.yaml

This last step will decrypt example.yaml using the test private key. To create your own secrets files using keys under your control, keep reading.

Usage

If you're using AWS KMS, create one or multiple master keys in the IAM console and export them, comma separated, in the SOPS_KMS_ARN env variable. It is recommended to use at least two master keys in different regions.

export SOPS_KMS_ARN="arn:aws:kms:us-east-1:656532927350:key/920aff2e-c5f1-4040-943a-047fa387b27e,arn:aws:kms:ap-southeast-1:656532927350:key/9006a8aa-0fa6-4c14-930e-a2dfb916de1d"

Your AWS credentials must be present in ~/.aws/credentials. sops uses boto3.

$ cat ~/.aws/credentials
[default]
aws_access_key_id = AKI.....
aws_secret_access_key = mw......

If you want to use PGP, export the fingerprints of the public keys, comma separated, in the SOPS_PGP_FP env variable.

export SOPS_PGP_FP="85D77543B3D624B63CEA9E6DBC17301B491B3F21,E60892BB9BD89A69F759A1A0A3D652173B763E8F"

Note: you can use both PGP and KMS simultaneously.

Then simply call sops with a file path as argument. It will handle the encryption/decryption transparently and open the cleartext file in an editor

$ sops mynewtestfile.yaml
mynewtestfile.yaml doesn't exist, creating it.
please wait while an encryption key is being generated and stored in a secure fashion
file written to mynewtestfile.yaml

. Editing will happen in whatever $EDITOR is set to, or, if it's not set, in vim. Keep in mind that sops will wait for the editor to exit, and then try to reencrypt the file. Some GUI editors (atom, sublime) spawn a child process and then exit immediately. They usually have an option to wait for the main editor window to be closed before exiting. See [#127]() for more information.

The resulting encrypted file looks like this:

myapp1: ENC[AES256_GCM,data:Tr7o=,iv:1=,aad:No=,tag:k=]
app2:
    db:
        user: ENC[AES256_GCM,data:CwE4O1s=,iv:2k=,aad:o=,tag:w==]
        password: ENC[AES256_GCM,data:p673w==,iv:YY=,aad:UQ=,tag:A=]
    # private key for secret operations in app2
    key: |-
        ENC[AES256_GCM,data:Ea3kL5O5U8=,iv:DM=,aad:FKA=,tag:EA==]
an_array:
- ENC[AES256_GCM,data:v8jQ=,iv:HBE=,aad:21c=,tag:gA==]
- ENC[AES256_GCM,data:X10=,iv:o8=,aad:CQ=,tag:Hw==]
- ENC[AES256_GCM,data:KN=,iv:160=,aad:fI4=,tag:tNw==]
sops:
    kms:
    -   created_at: 1441570389.775376
        enc: CiC....Pm1Hm
        arn: arn:aws:kms:us-east-1:656532927350:key/920aff2e-c5f1-4040-943a-047fa387b27e
    -   created_at: 1441570391.925734
        enc: Ci...awNx
        arn: arn:aws:kms:ap-southeast-1:656532927350:key/9006a8aa-0fa6-4c14-930e-a2dfb916de1d
    pgp:
    -   fp: 85D77543B3D624B63CEA9E6DBC17301B491B3F21
        created_at: 1441570391.930042
        enc: |
            -----BEGIN PGP MESSAGE-----
            hQIMA0t4uZHfl9qgAQ//UvGAwGePyHuf2/zayWcloGaDs0MzI+zw6CmXvMRNPUsA
            ...=oJgS
            -----END PGP MESSAGE-----

A copy of the encryption/decryption key is stored securely in each KMS and PGP block. As long as one of the KMS or PGP method is still usable, you will be able to access your data.

To decrypt a file in a cat fashion, use the -d flag:

$ sops -d mynewtestfile.yaml

sops encrypted files contain the necessary information to decrypt their content. All a user of sops needs is valid AWS credentials and the necessary permissions on KMS keys.

Given that, the only command a sops user needs is:

$ sops 

<file> will be opened, decrypted, passed to a text editor (vim by default), encrypted if modified, and saved back to its original location. All of these steps, apart from the actual editing, are transparent to the user.

Adding and removing keys

When creating new files, sops uses the PGP and KMS defined in the command line arguments --kms and --pgp, or from the environment variables SOPS_KMS_ARN and SOPS_PGP_FP. That information is stored in the file under the sops section, such that decrypting files does not require providing those parameters again.

Master PGP and KMS keys can be added and removed from a sops file in one of two ways: by using command line flag, or by editing the file directly.

Command line flag --add-kms, --add-pgp, --rm-kms and --rm-pgp can be used to add and remove keys from a file. These flags use the comma separated syntax as the --kms and --pgp arguments when creating new files.

# add a new pgp key to the file and rotate the data key
$ sops -r --add-pgp 85D77543B3D624B63CEA9E6DBC17301B491B3F21 example.yaml

# remove a pgp key from the file and rotate the data key
$ sops -r --rm-pgp 85D77543B3D624B63CEA9E6DBC17301B491B3F21 example.yaml

Alternatively, invoking sops with the flag -s will display the master keys while editing. This method can be used to add or remove kms or pgp keys under the sops section.

For example, to add a KMS master key to a file, add the following entry while editing:

sops:
    kms:
    - arn: arn:aws:kms:us-east-1:656532927350:key/920aff2e-c5f1-4040-943a-047fa387b27e

And, similarly, to add a PGP master key, we add its fingerprint:

sops:
    pgp:
    - fp: 85D77543B3D624B63CEA9E6DBC17301B491B3F21

When the file is saved, sops will update its metadata and encrypt the data key with the freshly added master keys. The removed entries are simply deleted from the file.

When removing keys, it is recommended to rotate the data key using -r, otherwise owners of the removed key may have add access to the data key in the past.

Assuming roles and using KMS in various AWS accounts

SOPS has the ability to use KMS in multiple AWS accounts by assuming roles in each account. Being able to assume roles is a nice feature of AWS that allows administrators to establish trust relationships between accounts, typically from the most secure account to the least secure one. In our use-case, we use roles to indicate that a user of the Master AWS account is allowed to make use of KMS master keys in development and staging AWS accounts. Using roles, a single file can be encrypted with KMS keys in multiple accounts, thus increasing reliability and ease of use.

You can use keys in various accounts by tying each KMS master key to a role that the user is allowed to assume in each account. The IAM roles documentation has full details on how this needs to be configured on AWS's side.

From the point of view of sops, you only need to specify the role a KMS key must assume alongside its ARN, as follows:

sops:
    kms:
    -   arn: arn:aws:kms:us-east-1:656532927350:key/920aff2e-c5f1-4040-943a-047fa387b27e
        role: arn:aws:iam::927034868273:role/sops-dev-xyz

The role must have permission to call Encrypt and Decrypt using KMS. An example policy is shown below.

{
  "Sid": "Allow use of the key",
  "Effect": "Allow",
  "Action": [
    "kms:Encrypt",
    "kms:Decrypt",
    "kms:ReEncrypt*",
    "kms:GenerateDataKey*",
    "kms:DescribeKey"
  ],
  "Resource": "*",
  "Principal": {
    "AWS": [
      "arn:aws:iam::927034868273:role/sops-dev-xyz"
    ]
  }
}

You can specify a role in the --kms flag and SOPS_KMS_ARN variable by appending it to the ARN of the master key, separated by a + sign:

+
arn:aws:kms:us-west-2:927034868273:key/fe86dd69-4132-404c-ab86-4269956b4500+arn:aws:iam::927034868273:role/sops-dev-xyz

AWS KMS Encryption Context

SOPS has the ability to use AWS KMS key policy and encryption context <> to refine the access control of a given KMS master key.

When creating a new file, you can specify encryption context in the --encryption-context flag by comma separated list of key-value pairs:

When creating a new file, you can specify encryption context in the --encryption-context flag by comma separated list of key-value pairs:

$ sops --encryption-context Environment:production,Role:web-server test.dev.yaml

The format of the Encrypt Context string is <EncryptionContext Key>:<EncryptionContext Value>,<EncryptionContext Key>:<EncryptionContext Value>,...

The encryption context will be stored in the file metadata and does not need to be provided at decryption.

Encryption contexts can be used in conjunction with KMS Key Policies to define roles that can only access a given context. An example policy is shown below:

{
  "Effect": "Allow",
  "Principal": {
    "AWS": "arn:aws:iam::111122223333:role/RoleForExampleApp"
  },
  "Action": "kms:Decrypt",
  "Resource": "*",
  "Condition": {
    "StringEquals": {
      "kms:EncryptionContext:AppName": "ExampleApp",
      "kms:EncryptionContext:FilePath": "/var/opt/secrets/"
    }
  }
}

Key Rotation

It is recommended to renew the data key on a regular basis. sops supports key rotation via the -r flag. Invoking it on an existing file causes sops to reencrypt the file with a new data key, which is then encrypted with the various KMS and PGP master keys defined in the file.

sops -r example.yaml

Using .sops.yaml conf to select KMS/PGP for new files

It is often tedious to specify the --kms and --pgp parameters for creation of all new files. If your secrets are stored under a specific directory, like a git repository, you can create a .sops.yaml configuration file at the root directory to define which keys are used for which filename.

Let's take an example:

• file named something.dev.yaml should use one set of KMS A
• file named something.prod.yaml should use another set of KMS B
• other files use a third set of KMS C
• all live under mysecretrepo/something.{dev,prod}.yaml

Under those circumstances, a file placed at mysecretrepo/.sops.yaml can manage the three sets of configurations for the three types of files:

# creation rules are evaluated sequentially, the first match wins
creation_rules:
    # upon creation of a file that matches the pattern *.dev.yaml,
    # KMS set A is used
    - filename_regex: \.dev\.yaml$
      kms: 'arn:aws:kms:us-west-2:927034868273:key/fe86dd69-4132-404c-ab86-4269956b4500,arn:aws:kms:us-west-2:361527076523:key/5052f06a-5d3f-489e-b86c-57201e06f31e+arn:aws:iam::361527076523:role/hiera-sops-prod'
      pgp: '1022470DE3F0BC54BC6AB62DE05550BC07FB1A0A'

    # prod files use KMS set B in the PROD IAM
    - filename_regex: \.prod\.yaml$
      kms: 'arn:aws:kms:us-west-2:361527076523:key/5052f06a-5d3f-489e-b86c-57201e06f31e+arn:aws:iam::361527076523:role/hiera-sops-prod,arn:aws:kms:eu-central-1:361527076523:key/cb1fab90-8d17-42a1-a9d8-334968904f94+arn:aws:iam::361527076523:role/hiera-sops-prod'
      pgp: '1022470DE3F0BC54BC6AB62DE05550BC07FB1A0A'

    # Finally, if the rules above have not matched, this one is a
    # catchall that will encrypt the file using KMS set C
    # The absence of a filename_regex means it will match everything
    - kms: 'arn:aws:kms:us-west-2:927034868273:key/fe86dd69-4132-404c-ab86-4269956b4500,arn:aws:kms:us-west-2:142069644989:key/846cfb17-373d-49b9-8baf-f36b04512e47,arn:aws:kms:us-west-2:361527076523:key/5052f06a-5d3f-489e-b86c-57201e06f31e'
      pgp: '1022470DE3F0BC54BC6AB62DE05550BC07FB1A0A'

When creating any file under mysecretrepo, whether at the root or under a subdirectory, sops will recursively look for a .sops.yaml file. If one is found, the filename of the file being created is compared with the filename regexes of the configuration file. The first regex that matches is selected, and its KMS and PGP keys are used to encrypt the file.

Creating a new file with the right keys is now as simple as

$ sops .prod.yaml

Note that the configuration file is ignored when KMS or PGP parameters are passed on the sops command line or in environment variables.

Specify a different GPG executable

sops checks for the SOPS_GPG_EXEC environment variable. If specified, it will attempt to use the executable set there instead of the default of gpg.

Example: place the following in your ~/.bashrc

SOPS_GPG_EXEC = 'your_gpg_client_wrapper'

Important information on types

YAML and JSON type extensions

sops uses the file extension to decide which encryption method to use on the file content. YAML and JSON files are treated as trees of data, and key/values are extracted from the files to only encrypt the leaf values. The tree structure is also used to check the integrity of the file.

Therefore, if a file is encrypted using a specific format, it need to be decrypted in the same format. The easiest way to achieve this is to conserve the original file extension after encrypting a file. For example:

$ sops -e -i myfile.json

$ sops -d myfile.json

If you want to change the extension of the file once encrypted, you need to provide sops with the --input-type flag upon decryption. For example:

$ sops -e myfile.json > myfile.json.enc

$ sops -d --input-type json myfile.json.enc

YAML anchors

sops only supports a subset of YAML's many types. Encrypting YAML files that contain strings, numbers and booleans will work fine, but files that contain anchors will not work, because the anchors redefine the structure of the file at load time.

This file will not work in `sops`:

bill-to:  &id001
    street: |
        123 Tornado Alley
        Suite 16
    city:   East Centerville
    state:  KS

ship-to:  *id001

sops uses the path to a value as additional data in the AEAD encryption, and thus dynamic paths generated by anchors break the authentication step.

JSON and TEXT file types do not support anchors and thus have no such limitation.

Top-level arrays

YAML and JSON top-level arrays are not supported, because sops needs a top-level sops key to store its metadata. This file will not work in sops:

---
  - some
  - array
  - elements

But this one will because because the sops key can be added at the same level as the data key.

data:
  - some
  - array
  - elements

Similarly, with JSON arrays, this document will not work:

[
  "some",
  "array",
  "elements"
]

But this one will work just fine:

{
  "data": [
    "some",
    "array",
    "elements"
  ]
}

Examples

Take a look into the examples folder for detailed use cases of sops in a CI environment. The section below describes specific tips for common use cases.

Creating a new file

The command below creates a new file with a data key encrypted by KMS and PGP.

$ sops --kms "arn:aws:kms:us-west-2:927034868273:key/fe86dd69-4132-404c-ab86-4269956b4500" --pgp C9CAB0AF1165060DB58D6D6B2653B624D620786D /path/to/new/file.yaml

Encrypting an existing file

Similar to the previous command, we tell sops to use one KMS and one PGP key. The path points to an existing cleartext file, so we give sops flag -e to encrypt the file, and redirect the output to a destination file.

$ export SOPS_KMS_ARN="arn:aws:kms:us-west-2:927034868273:key/fe86dd69-4132-404c-ab86-4269956b4500"
$ export SOPS_PGP_FP="C9CAB0AF1165060DB58D6D6B2653B624D620786D"
$ sops -e /path/to/existing/file.yaml > /path/to/new/encrypted/file.yaml

Decrypt the file with -d.

$ sops -d /path/to/new/encrypted/file.yaml

Encrypt or decrypt a file in place

Rather than redirecting the output of -e or -d, sops can replace the original file after encrypting or decrypting it.

# file.yaml is in cleartext
$ sops -e -i /path/to/existing/file.yaml
# file.yaml is now encrypted
$ sops -d -i /path/to/existing/file.yaml
# file.yaml is back in cleartext

Encrypting binary files

sops primary use case is encrypting YAML and JSON configuration files, but it also has the ability to manage binary files. When encrypting a binary, sops will read the data as bytes, encrypt it, store the encrypted base64 under tree['data'] and write the result as JSON.

Note that the base64 encoding of encrypted data can actually make the encrypted file larger than the cleartext one.

In-place encryption/decryption also works on binary files.

$ dd if=/dev/urandom of=/tmp/somerandom bs=1024
count=512
512+0 records in
512+0 records out
524288 bytes (524 kB) copied, 0.0466158 s, 11.2 MB/s

$ sha512sum /tmp/somerandom
9589bb20280e9d381f7a192000498c994e921b3cdb11d2ef5a986578dc2239a340b25ef30691bac72bdb14028270828dad7e8bd31e274af9828c40d216e60cbe /tmp/somerandom

$ sops -e -i /tmp/somerandom
please wait while a data encryption key is being generated and stored securely

$ sops -d -i /tmp/somerandom

$ sha512sum /tmp/somerandom
9589bb20280e9d381f7a192000498c994e921b3cdb11d2ef5a986578dc2239a340b25ef30691bac72bdb14028270828dad7e8bd31e274af9828c40d216e60cbe /tmp/somerandom

Extract a sub-part of a document tree

sops can extract a specific part of a YAML or JSON document, by provided the path in the --extract command line flag. This is useful to extract specific values, like keys, without needing an extra parser.

$ sops -d ~/git/svc/sops/example.yaml --extract '["app2"]["key"]'
-----BEGIN RSA PRIVATE KEY-----
MIIBPAIBAAJBAPTMNIyHuZtpLYc7VsHQtwOkWYobkUblmHWRmbXzlAX6K8tMf3Wf
ImcbNkqAKnELzFAPSBeEMhrBN0PyOC9lYlMCAwEAAQJBALXD4sjuBn1E7Y9aGiMz
bJEBuZJ4wbhYxomVoQKfaCu+kH80uLFZKoSz85/ySauWE8LgZcMLIBoiXNhDKfQL
vHECIQD6tCG9NMFWor69kgbX8vK5Y+QL+kRq+9HK6yZ9a+hsLQIhAPn4Ie6HGTjw
fHSTXWZpGSan7NwTkIu4U5q2SlLjcZh/AiEA78NYRRBwGwAYNUqzutGBqyXKUl4u
Erb0xAEyVV7e8J0CIQC8VBY8f8yg+Y7Kxbw4zDYGyb3KkXL10YorpeuZR4LuQQIg
bKGPkMM4w5blyE1tqGN0T7sJwEx+EUOgacRNqM2ljVA=
-----END RSA PRIVATE KEY-----

The tree path syntax uses regular python dictionary syntax, without the variable name. Extract keys by naming them, and array elements by numbering them.

$ sops -d ~/git/svc/sops/example.yaml --extract '["an_array"][1]'
secretuser2

Set a sub-part in a document tree

sops can set a specific part of a YAML or JSON document, by providing the path and value in the --set command line flag. This is useful to set specific values, like keys, without needing an editor.

$ sops ~/git/svc/sops/example.yaml --set '["app2"]["key"]' '"app2keystringvalue"'

The tree path syntax uses regular python dictionary syntax, without the variable name. Set to keys by naming them, and array elements by numbering them.

$ sops ~/git/svc/sops/example.yaml --set '["an_array"][1]' '"secretuser2"'

The value must be formatted as json.

$ sops ~/git/svc/sops/example.yaml --set '["an_array"][1]' '{"uid1":null,"uid2":1000,"uid3":["bob"]}'

Using sops as a library in a python script

You can import sops as a module and use it in your python program.

import sops

pathtype = sops.detect_filetype(path)
tree = sops.load_file_into_tree(path, pathtype)
sops_key, tree = sops.get_key(tree)
tree = sops.walk_and_decrypt(tree, sops_key)
sops.write_file(tree, path=path, filetype=pathtype)

Showing diffs in cleartext in git

You most likely want to store encrypted files in a version controlled repository. Sops can be used with git to decrypt files when showing diffs between versions. This is very handy for reviewing changes or visualizing history.

To configure sops to decrypt files during diff, create a .gitattributes file at the root of your repository that contains a filter and a command.

... code:

*.yaml diff=sopsdiffer

Here we only care about YAML files. sopsdiffer is an arbitrary name that we map to a sops command in the git configuration file of the repository.

$ git config diff.sopsdiffer.textconv "sops -d"

$ grep -A 1 sopsdiffer .git/config
[diff "sopsdiffer"]
    textconv = "sops -d"

With this in place, calls to git diff will decrypt both previous and current versions of the target file prior to displaying the diff. And it even works with git client interfaces, because they call git diff under the hood!

Encrypting only parts of a file

Note: this only works on YAML and JSON files, not on BINARY files.

By default, sops encrypts all the values of a YAML or JSON file and leaves the keys in cleartext. In some instances, you may want to exclude some values from being encrypted. This can be accomplished by adding the suffix _unencrypted to any key of a file. When set, all values underneath the key that set the _unencrypted prefix will be left in cleartext.

Note that, while in cleartext, unencrypted content is still added to the checksum of the file, and thus cannot be modified outside of sops without breaking the file integrity check.

The unencrypted suffix can be set to a different value using the --unencrypted-suffix option.

Encryption Protocol

When sops creates a file, it generates a random 256 bit data key and asks each KMS and PGP master key to encrypt the data key. The encrypted version of the data key is stored in the sops metadata under sops.kms and sops.pgp.

For KMS:

sops:
    kms:
    -   enc: CiC6yCOtzsnFhkfdIslYZ0bAf//gYLYCmIu87B3sy/5yYxKnAQEBAQB4usgjrc7JxYZH3SLJWGdGwH//4GC2ApiLvOwd7Mv+cmMAAAB+MHwGCSqGSIb3DQEHBqBvMG0CAQAwaAYJKoZIhvcNAQcBMB4GCWCGSAFlAwQBLjARBAyGdRODuYMHbA8Ozj8CARCAO7opMolPJUmBXd39Zlp0L2H9fzMKidHm1vvaF6nNFq0ClRY7FlIZmTm4JfnOebPseffiXFn9tG8cq7oi
        enc_ts: 1439568549.245995
        arn: arn:aws:kms:us-east-1:656532927350:key/920aff2e-c5f1-4040-943a-047fa387b27e

For PGP:

sops:
    pgp:
    -   fp: 85D77543B3D624B63CEA9E6DBC17301B491B3F21
        created_at: 1441570391.930042
        enc: |
            -----BEGIN PGP MESSAGE-----
            Version: GnuPG v1

            hQIMA0t4uZHfl9qgAQ//UvGAwGePyHuf2/zayWcloGaDs0MzI+zw6CmXvMRNPUsA
            pAgRKczJmDu4+XzN+cxX5Iq9xEWIbny9B5rOjwTXT3qcUYZ4Gkzbq4MWkjuPp/Iv
            qO4MJaYzoH5YxC4YORQ2LvzhA2YGsCzYnljmatGEUNg01yJ6r5mwFwDxl4Nc80Cn
            RwnHuGExK8j1jYJZu/juK1qRbuBOAuruIPPWVdFB845PA7waacG1IdUW3ZtBkOy3
            O0BIfG2ekRg0Nik6sTOhDUA+l2bewCcECI8FYCEjwHm9Sg5cxmP2V5m1mby+uKAm
            kewaoOyjbmV1Mh3iI1b/AQMr+/6ZE9MT2KnsoWosYamFyjxV5r1ZZM7cWKnOT+tu
            KOvGhTV1TeOfVpajNTNwtV/Oyh3mMLQ0F0HgCTqomQVqw5+sj7OWAASuD3CU/dyo
            pcmY5Qe0TNL1JsMNEH8LJDqSh+E0hsUxdY1ouVsg3ysf6mdM8ciWb3WRGxih1Vmf
            unfLy8Ly3V7ZIC8EHV8aLJqh32jIZV4i2zXIoO4ZBKrudKcECY1C2+zb/TziVAL8
            qyPe47q8gi1rIyEv5uirLZjgpP+JkDUgoMnzlX334FZ9pWtQMYW4Y67urAI4xUq6
            /q1zBAeHoeeeQK+YKDB7Ak/Y22YsiqQbNp2n4CKSKAE4erZLWVtDvSp+49SWmS/S
            XgGi+13MaXIp0ecPKyNTBjF+NOw/I3muyKr8EbDHrd2XgIT06QXqjYLsCb1TZ0zm
            xgXsOTY3b+ONQ2zjhcovanDp7/k77B+gFitLYKg4BLZsl7gJB12T8MQnpfSmRT4=
            =oJgS
            -----END PGP MESSAGE-----

sops then opens a text editor on the newly created file. The user adds data to the file and saves it when done.

Upon save, sops browses the entire file as a key/value tree. Every time sops encounters a leaf value (a value that does not have children), it encrypts the value with AES256_GCM using the data key and a 256 bit random initialization vector.

Each file uses a single data key to encrypt all values of a document, but each value receives a unique initialization vector and has unique authentication data.

Additional data is used to guarantee the integrity of the encrypted data and of the tree structure: when encrypting the tree, key names are concatenated into a byte string that is used as AEAD additional data (aad) when encrypting values. We expect that keys do not carry sensitive information, and keeping them in cleartext allows for better diff and overall readability.

Any valid KMS or PGP master key can later decrypt the data key and access the data.

Multiple master keys allow for sharing encrypted files without sharing master keys, and provide a disaster recovery solution. The recommended way to use sops is to have two KMS master keys in different regions and one PGP public key with the private key stored offline. If, by any chance, both KMS master keys are lost, you can always recover the encrypted data using the PGP private key.

Message Authentication Code

In addition to authenticating branches of the tree using keys as additional data, sops computes a MAC on all the values to ensure that no value has been added or removed fraudulently. The MAC is stored encrypted with AES_GCM and the data key under tree->sops->mac.

Motivation

Automating the distribution of secrets and credentials to components of an infrastructure is a hard problem. We know how to encrypt secrets and share them between humans, but extending that trust to systems is difficult. Particularly when these systems follow devops principles and are created and destroyed without human intervention. The issue boils down to establishing the initial trust of a system that just joined the infrastructure, and providing it access to the secrets it needs to configure itself.

The initial trust

In many infrastructures, even highly dynamic ones, the initial trust is established by a human. An example is seen in Puppet by the way certificates are issued: when a new system attempts to join a Puppetmaster, an administrator must, by default, manually approve the issuance of the certificate the system needs. This is cumbersome, and many puppetmasters are configured to auto-sign new certificates to work around that issue. This is obviously not recommended and far from ideal.

AWS provides a more flexible approach to trusting new systems. It uses a powerful mechanism of roles and identities. In AWS, it is possible to verify that a new system has been granted a specific role at creation, and it is possible to map that role to specific resources. Instead of trusting new systems directly, the administrator trusts the AWS permission model and its automation infrastructure. As long as AWS keys are safe, and the AWS API is secure, we can assume that trust is maintained and systems are who they say they are.

KMS, Trust and secrets distribution

Using the AWS trust model, we can create fine grained access controls to Amazon's Key Management Service (KMS). KMS is a service that encrypts and decrypts data with AES_GCM, using keys that are never visible to users of the service. Each KMS master key has a set of role-based access controls, and individual roles are permitted to encrypt or decrypt using the master key. KMS helps solve the problem of distributing keys, by shifting it into an access control problem that can be solved using AWS's trust model.

Operational requirements

When Mozilla's Services Operations team started revisiting the issue of distributing secrets to EC2 instances, we set a goal to store these secrets encrypted until the very last moment, when they need to be decrypted on target systems. Not unlike many other organizations that operate sufficiently complex automation, we found this to be a hard problem with a number of prerequisites:

1. Secrets must be stored in YAML files for easy integration into hiera
2. Secrets must be stored in GIT, and when a new CloudFormation stack is built, the current HEAD is pinned to the stack. (This allows secrets to be changed in GIT without impacting the current stack that may autoscale).
3. Entries must be encrypted separately. Encrypting entire files as blobs makes git conflict resolution almost impossible. Encrypting each entry separately is much easier to manage.
4. Secrets must always be encrypted on disk (admin laptop, upstream git repo, jenkins and S3) and only be decrypted on the target systems

SOPS can be used to encrypt YAML, JSON and BINARY files. In BINARY mode, the content of the file is treated as a blob, the same way PGP would encrypt an entire file. In YAML and JSON modes, however, the content of the file is manipulated as a tree where keys are stored in cleartext, and values are encrypted. hiera-eyaml does something similar, and over the years we learned to appreciate its benefits, namely:

• diffs are meaningful. If a single value of a file is modified, only that value will show up in the diff. The diff is still limited to only showing encrypted data, but that information is already more granular that indicating that an entire file has changed.
• conflicts are easier to resolve. If multiple users are working on the same encrypted files, as long as they don't modify the same values, changes are easy to merge. This is an improvement over the PGP encryption approach where unsolvable conflicts often happen when multiple users work on the same file.

OpenPGP integration

OpenPGP gets a lot of bad press for being an outdated crypto protocol, and while true, what really made us look for alternatives is the difficulty of managing and distributing keys to systems. With KMS, we manage permissions to an API, not keys, and that's a lot easier to do.

But PGP is not dead yet, and we still rely on it heavily as a backup solution: all our files are encrypted with KMS and with one PGP public key, with its private key stored securely for emergency decryption in the event that we lose all our KMS master keys.

SOPS can be used without KMS entirely, the same way you would use an encrypted PGP file: by referencing the pubkeys of each individual who has access to the file. It can easily be done by providing sops with a comma-separated list of public keys when creating a new file:

$ sops --pgp "E60892BB9BD89A69F759A1A0A3D652173B763E8F,84050F1D61AF7C230A12217687DF65059EF093D3,85D77543B3D624B63CEA9E6DBC17301B491B3F21" mynewfile.yaml

Threat Model

The security of the data stored using sops is as strong as the weakest cryptographic mechanism. Values are encrypted using AES256_GCM which is the strongest symetric encryption algorithm known today. Data keys are encrypted in either KMS, which also uses AES256_GCM, or PGP which uses either RSA or ECDSA keys.

Going from the most likely to the least likely, the threats are as follows:

Compromised AWS credentials grant access to KMS master key

An attacker with access to an AWS console can grant itself access to one of the KMS master keys used to encrypt a sops data key. This threat should be mitigated by protecting AWS accesses with strong controls, such as multi-factor authentication, and also by performing regular audits of permissions granted to AWS users.

Compromised PGP key

PGP keys are routinely mishandled, either because owners copy them from machine to machine, or because the key is left forgotten on an unused machine an attacker gains access to. When using PGP encryption, sops users should take special care of PGP private keys, and store them on smart cards or offline as often as possible.

Factorized RSA key

sops doesn't apply any restriction on the size or type of PGP keys. A weak PGP keys, for example 512 bits RSA, could be factorized by an attacker to gain access to the private key and decrypt the data key. Users of sops should rely on strong keys, such as 2048+ bits RSA keys, or 256+ bits ECDSA keys.

Weak AES cryptography

A vulnerability in AES256_GCM could potentially leak the data key or the KMS master key used by a sops encrypted file. While no such vulnerability exists today, we recommend that users keep their encrypted files reasonably private.

Backward compatibility

sops will remain backward compatible on the major version, meaning that all improvements brought to the 1.X branch (current) will maintain the file format introduced in 1.0.

License

Mozilla Public License Version 2.0

Authors

• Julien Vehent <> (lead & maintainer)
• Daniel Thornton <>
• Alexis Metaireau <>
• Rémy Hubscher <>
• Todd Wolfson <>
• Brian Hourigan <>

Credits

sops is inspired by hiera-eyaml, credstash , sneaker, password store and too many years managing PGP encrypted files by hand...