KMS-proxy

Encrypts data with a key chain. The key chain is one or more AES-128bit keys. There is only one primary key, which is used for encryption. Depending on the prefix, older keys are used from the keychain. The key chain needs to be stored.

This key chain can be used as a KMS-plugin. Instead of a KMS-provider an HMS can be used.

There are different storage options:

• store along every ciphertext and
• store in "etcd".

Why

The goal is to call a KMS-provider less often. By adding an additional key- layer, the calls to a KMS-provider can be reduced by up to 2^21 calls.

This can be highly beneficial, as every call to a KMS-provider generates costs. The costs could be monetary or temporary.

Next

1. Hook up KMS.
2. Hook up PKCS #11.
3. Hook up passphrase.

Details

Naming

• root key is an external key that encrypts the key chain
• key chain is a KEK and a counter that limits the usage to secure defaults
• KEK is a set of keys with one key being the primary key.
• DEK is a key used once for encryption of data.
• ciphertext is data that got encrypted.
• encrypted data is the ciphertext and the DEK.

Key Hierarchy

graph TD
    rk[root key] --> KEK
    KEK --> DEK_1
    KEK --> DEK_2
    KEK --> DEK_n

Loading

Data is encrypted with an individual key, called data encryption key (DEK). The DEKs are encrypted with a key encryption key (KEK). The KEK is encrypted with a root key that comes from the KMS-provider, HMS or passphrase.

The encrypted DEK is stored alongside the encrypted data and cached in memory.

The encrypted KEK is stored is stored, where configured.

Encryption

The encryption algorithm is AES, in GCM mode with a 128 bit key. 128 bit key should be enough. Impossible is impossible*. A good key hygiene is more improtant.

The KEK rotates when necessary automatically to keep the data safe.

* Until we have quantum-computing on the same level as we have non-quantum-computing. As it can compute like the key size would be cut in half.

Usage

Start anew:

keyChain, err := kms.New()
if err != nil {
  return err
}

// encryptedData and not cipher text as it contains encrypted DEK
encryptedData, err := keyChain.Encrypt([]byte(plaintext))
if err != nil {
  return err
}

plainTextAsBytes, err := keyChain.Decrypt(encryptedData)
if err != nil {
  return err
}

if !bytes.Equal([]byte(plaintext), plainTextAsBytes) {
  panic(errors.New("PRs are welcome!"))
}

Start from io.Reader:

// TODO

Start from external_kms:

// TODO

Start from hms:

// TODO