GO - Key Management Service

A REST based Key Management Service written in GO.

What is GO-KMS?

GO-KMS is a encryption Key Management Service in GO. Modelled extensively on AWS KMS behaviour, the API is used for symmetrical key management. It offers Cryptography as a Service (CaaS) functionality such as encryption/decryption/reencryption without exposing keys.

The crypto provider is based on AES and a key size of 256bits using the GCM cipher to provide confidentiality as well as authentication.

Keys are encrypted and stored on disk, using a master key which is derived using PBKDF2 from a passphrase when run in pure software mode. It is also possible to combine GO-KMS with a Hardware Security Module (HSM) which can be leveraged to create and encrypt a master key using the HSM for generation and protection. HSM support is done using the PKCS#11 standard.

GO-KMS authentication is done using HMAC-SHA256 over HTTPS.

GO-KMS - Command Line Interface

GO-KMS-CLI is a command line interface which can be used to manage and interact with go-kms. The project can be found here: https://github.com/keithballdotnet/go-kms-cli

Features

• AES Key store
• Cryptography as a Service
  • Encrypt
  • Decrypt
  • Re-encrypt
• Keys encrypted while at rest
• Shared-key Authentication
• Playground for HSM support via SoftHSM2 and PKCS#11

Todo

• Some documentation about the keys
• RSA Encryption provider
• Automatic key rotation?
• Full HSM provider support

How-To

To run get the project...

go get github.com/keithballdotnet/go-kms

The dependencies are in the vendor folder already, but should you want to you can run ...

dep ensure

You need to set the following variables:

export GOKMS_AUTH_KEY=/path/to/auth.key
export GOKMS_CRYPTO_PROVIDER= hsm | gokms
export GOKMS_HOST=localhost
export GOKMS_PORT=8020
export GOKMS_SSL_CERT=/path/to/ssl_cert.pem
export GOKMS_SSL_KEY=/path/to/ssl_key.pem

If the GOKMS_CRYPTO_PROVIDER is set to "gokms" then you also need to set:

export GOKMS_KSMC_PATH=/path/to/keys/
export GOKMS_KSMC_PASSPHRASE="a very long Passphrase that will be used for key derivation"

If the GOKMS_CRYPTO_PROVIDER is set to "hsm" then you also need to set:

export GOKMS_HSM_LIB=/path/to/your/hsm/lib.so
export GOKMS_HSM_SLOT="0"
export GOKMS_HSM_AES_KEYID="TheNameOfTheCryptoKey"

# optional: If not set no pkcs11 login will be performed.  Useful for Tokens with no PIN set.
export GOKMS_HSM_SLOT_PIN="1234"

Authorization

Authorization is done via a Authorization header sent in a request. Anonymous requests are not allowed. To authenticate a request, you must sign the request with the shared key when making the request and pass that signature as part of the request.

Here you can see an example of a Authorization header

Authorization=RvPtP0QB7iIun1ehwheD4YUo7+fYfw7/ywl+HsC5Ddk=

You construct the signature is built in the following format:

authRequestSig = method + "\n" +
                 Date + "\n" +
                 resource

This would result in the following signature to be signed:

POST\nWed, 28 Jan 2015 10:42:13 UTC\n/api/v1/go-ksm

Note that you MUST past the same date value in the request. Date should be supplied in UTC using RFC1123 format.

x-kms-date=Wed, 28 Jan 2015 10:42:13 UTC

The signature must be exactly in the same order and include the new line character.

Now encode the signature using the HMAC-SHA256 algorithm using the shared key.

This will result in a key like this:

RvPtP0QB7iIun1ehwheD4YUo7+fYfw7/ywl+HsC5Ddk="

Example go code to create the signature

date := time.Now().UTC().Format(time.RFC1123) // UTC time
request.Header.Add("x-kms-date", date)

authRequestKey := fmt.Sprintf("%s\n%s\n%s", method, date, resource)

// See package http://golang.org/pkg/crypto/hmac/ on how golang creates hmacs
hmac := crypto.GetHmac256(authRequestKey, SharedKey)  

request.Header.Add("Authorization", hmac)

Good resources:

KMS

• AWS KMS: https://d0.awsstatic.com/whitepapers/KMS-Cryptographic-Details.pdf
• MS Key Vault: https://msdn.microsoft.com/en-US/library/azure/dn903623

PKCS#11

• https://github.com/miekg/pkcs11
• http://www-01.ibm.com/support/knowledgecenter/linuxonibm/com.ibm.linux.z.lxce/lxce_linklib_object_samples.html

HSM

• https://www.opendnssec.org/
• SofthHsm2 only supports RSA encryption: https://wiki.opendnssec.org/display/SoftHSM/v2+Requirements
• https://wiki.opendnssec.org/display/SoftHSMDOCS/SoftHSM+Documentation+v2.0
• http://docs.oracle.com/javase/7/docs/technotes/guides/security/p11guide.html

Install notes if building SofthHsm2 support:

Add some missing things needed to build, pkcs11

sudo yum install libtool-ltdl-devel

Install softhsm2

sudo yum-config-manager --add-repo http://copr-fe.cloud.fedoraproject.org/coprs/pspacek/softhsm2/
sudo yum install softhsm2

Create a place to store the tokens

mkdir /home/keithball/Documents/tokens

Create/change config file to reflect new token location

# SoftHSM v2 configuration file

directories.tokendir = /home/keithball/Documents/tokens
objectstore.backend = file

# ERROR, WARNING, INFO, DEBUG
log.level = DEBUG

Create initial token...

export SOFTHSM2_CONF=$PWD/softhsm2.conf
softhsm2-util --init-token --slot 0 --label "My token 1"

Check it worked ok

softhsm2-util --show-slots