Shush!

"shush" is a small tool that can be used to encrypt and decrypt secrets, using the AWS "Key Management Service" (KMS).

Usage

Encrypting things

Encrypt secrets like this:

shush encrypt KEY-ID-OR-ALIAS < secret.txt > secret.encrypted

The output of encrypt is Base64-encoded ciphertext.

KEY-ID-OR-ALIAS can be the id or ARN of a KMS master key, or alias prefixed by "alias/", or simply just the alias.

Plaintext input can also be provided on the command-line, e.g.

shush encrypt KEY-ID 'this is a secret' > secret.encrypted

With the -t or --trim flag, encrypt will automatically remove leading and trailing whitespace from the plaintext. This can be especially useful when piping input from commands which always leave a trailing newline.

shush encrypt -t KEY_ID ' I don't really need this whitespace ' > secret.encrypted

Decrypting things

Encrypted secrets are easy to decrypt, like this:

shush decrypt < secret.encrypted > secret.txt

There's no need to specify a KEY-ID here, as it's encoded in the ciphertext.

Finding the key that was used

If you want to see the ARN of the key used to encrypt the secret, add the --print-key flag

shush decrypt --print-key < secret.encrypted

Credentials and region

Appropriate AWS credentials must be provided by one of the mechanisms supported by aws-sdk-go, e.g. environment variables, or EC2 instance profile.

When used within EC2, shush selects the appropriate region automatically. Outside EC2, you'll need to specify it, via --region or by setting $AWS_DEFAULT_REGION.

Encryption context

"shush" supports KMS encryption contexts, which may be used to scope use of a key. The same encryption context must be provided when encrypting and decrypting.

shush --context app=myapp encrypt KEY-ID secret.txt > secret.encrypted
shush --context app=myapp decrypt < secret.encrypted > secret.txt

Limitations

"shush" can only encrypt small amounts of data; up to 4 KB.

Use as a command shim

"shush exec" is a command shim that makes it easy to use secrets transported via the (Unix) process environment. It decrypts any environment variables prefixed by "KMS_ENCRYPTED_", and executes a specified command.

For example:

$ export KMS_ENCRYPTED_DB_PASSWORD=$(shush encrypt alias/app-secrets 'seasame')
$ shush exec -- env | grep PASSWORD
KMS_ENCRYPTED_DB_PASSWORD=CiAbQLOo2VC4QTV/Ng986wsDSJ0srAe6oZnLyzRT6pDFWRKOAQEBAgB4G0CzqNlQuEE1fzYPfOsLA0idLKwHuqGZy8s0U+qQxVkAAABlMGMGCSqGSIb3DQEHBqBWMFQCAQAwTwYJKoZIhvcNAQcBMB4GCWCGSAFlAwQBLjARBAzfFR0tsHRq18JUhMcCARCAImvuMNYuHUut3BT7sZs9a31qWcmOBUBXYEsD+kx2GxUxBPE=
DB_PASSWORD=seasame

In this example, "shush exec":

found $KMS_ENCRYPTED_DB_PASSWORD in the environment
decrypted the contents
put the result in $DB_PASSWORD
executed env

"shush exec" works well as an entrypoint for Docker images, e.g.

# Include "shush" to decode KMS_ENCRYPTED_STUFF
ARG TARGETARCH
RUN curl -fsSL -o /usr/local/bin/shush \
    https://github.com/realestate-com-au/shush/releases/download/v1.5.4/shush_linux_${TARGETARCH} \
 && chmod +x /usr/local/bin/shush
ENTRYPOINT ["/usr/local/bin/shush", "exec", "--"]

Installation

Binaries for official releases may be downloaded from the releases page on GitHub.

If you want to compile it from source, try:

$ go get github.com/realestate-com-au/shush

For Unix/Linux users, you can install shush using the following command. You may want to change the version number in the command below from v1.5.4 to whichever version you want:

sudo curl -fsSL -o /usr/local/bin/shush \
    "https://github.com/realestate-com-au/shush/releases/download/v1.5.4/shush_$(uname -s | tr '[:upper:]' '[:lower:]')_$(uname -m | sed 's/x86_/amd/' | sed 's/aarch/arm/')" \
 && sudo chmod +x /usr/local/bin/shush

Examples

Encrypt a password

Encrypt user input:

echo -n "Enter password: "
ENCRYPTED_PASSWORD=$(shush encrypt alias/app-secrets)

and later:

some-command --password $(shush decrypt "$ENCRYPTED_PASSWORD")

Bulk encryption of secrets

Encrypt some environment variables, as though they were arguments to env(1):

shush encrypt alias/app-secrets 'FOO=1 BAR=2' > secrets

and later:

env $(shush decrypt < secrets) some-command

Releasing a new version

Please see docs/releasing.md

License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Contributing

Source-code for shush is on Github.

realestate-com-au/shush

realestate-com-au

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