Study Guides/AWS Cybersecurity Notes/Amazon KMS

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Overview

  • Data encryption is the most critical aspect.
  • Must know KMS and the API calls used in the service


Two types of encryption:

  • Symmetric - Same key
This is fast for large ammounts of data.
  • Asymmetric - Uses a pair of keys
Private key - Kept secret (Decripts data)
Public key - Distributed (Encrypts data)


Exaples of symmetric are AES and DES


AWS KMS

Customer Master Keys

  • Contain key material for encryption and decryption.
  • CMKs are managed in KMS
  • Think of CMK as a keychain
  • KMS provides a way to store and manage keys - this is the AWS lockbox for your keys
  • KMS protects the CMKs
  • Uses industry standard practices to safeguard CMK


About CMKs:


  • They manage encryption keys for sensative data.
  • Control encryption and decryption of data
  • Securely stored by KMS
  • Fine grained access control
  • Work inside and ourside of AWS
  • use envelope encryption.
A data key is generated and used for encrypting data.
That key is encrypted with the CMK.
  • Auditable in AWS Cloud Trail and AWS Cloud Watch


  • Two different types of CMK exist:
  • Customer managed.
  • AWS managed.


AWS Managed CMKs

  • Owned and used by AWS services
  • Independent from the customer account.
You cannot track their useage or audit them!
  • Can be used by services inside an account.
  • They are maintained in MKS and provide a quick way to implement encryption.
  • They are rotated at least once per year.
  • No control over when these keys roll.
  • These keys are region specific.


Examples of AWS Managed CMKs

  • AWS managed CMK for S3 - Used in data buckets.
  • AWS KMS Default CMK - used for default encryption in EBS, RDS and Redshift.



Customer Managed Keys

Provides the customer total control over the key.

Customer has complete control over the lifecycle of a key.
This provides greater flexibility and customization.


The key Policy can be defined:

  • Rotation schedules.
  • Permissions based on requirements.


These keys are not tied to any feature or service.

  • They can be used inside or outside of AWS.
  • Much more contol over key use and permissions.


It is the customer responsibility to protect customer managed keys.

KMS provides the rools and security measures - but security is on the customer.


Selecting a key type

  • Policy will dictate the key type.
  • AWS managed keys may be ok if complete control is not needed.
  • AWS managed keys have no charge.
  • If policy states keys must be rotated on demand (after an incident) customer managed is best.


Data Encryption Keys

These are generated by KMS for encrypting data.

They are used WITH customer-managed keys to protect infomation.

They are short lived - only used for specific encryption operations.

DEKs proide an extra layer of security:

DEK - Encrypts the data
CMK - Encrypts the DEK


About DEKs:

  • Managed and generated in KMS
  • Used with CMK's
  • They are randomly generated.
  • Use envelope encryption Encrypted > DEC > CMK > Decrypted
  • DEKs are fast and efficient.
  • Can be used with vrious AWS services
  • KMS manages the DEC lifecycle.
  • Important part: DECs are symmetrical keys!


Key Material

Key material is used to encryptd and decrypt.

  • Customers cannot manage the key material in any way!
  • The key material is inside the CMK.
  • The CMK material is used to create the DMK
  • AWS Manged CMK - automatically creates the material inside the CMK.
  • For cusomter manaaged CMK - you create the CMK and import your own key material.


Importing key material

This may be needed if you have keys in use outside of AWS and need to bring them in.

This also could be for regulatary needs.

To do this:

Import (external) key material under advanced options


  • The key materlal must be in binary format.
  • An experation date can be provided.
If the expration date is reached or the material is deleted it is gone forever.
  • If imported key material is used the key must be manually rotated.


Key Policies

These control acess to KMS kets.

Each KMS key is associated with a policy that defines who can use the key.

The policy enfoces secure granular access control.


Key Grants

Allows contol and management of cryptographic functions on keys.

You define a AWS IAM user role or AWS account to provide access.

You then speficy what actions should be allowed by that principle.


This allows find graned control over keys.


What about Envelope encryption

  • Data is encrypted.
  • The key for the data is also encrypted by another key.


The top level key is know as a master key.


How it works in KMS

Customer mater key: This is a symmetric key managed by KMS,

DEK: Used when data needs to be encrypted.

Enveloping the DEK: The DEK is encrypted with the master key.
Storing the DEK: The encrypted DEK - known as the envelope key is stored with the data.
Decrypting the enevelpe key: the DEK (envelope key) is passed to KMS from storage.
Decrypting data: The decrypted DEK (decrytped by KMS) is used to decrypt the data.


This has seneral advantages:

  • The master key never leaves KMS.
  • The DEK is proected and seperate from the data.
  • Granular control is enabled through KMS.
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