Google Cloud KMS Key Management Service

Google Cloud KMS Key Management Service

  • Google Cloud KMS – Key Management Service provides a centralized, scalable, fast cloud key management service to manage encryption keys
  • KMS helps apply hardware security modules (HSMs) effortlessly to the most sensitive data by just a toggle between software- and hardware-protected encryption keys with the press of a button.
  • KMS provides support for external keys using Cloud External Key Manager to protect the data in Google Cloud and separate the data from the key

Cloud KMS Keys, Keys Versions, and Key Rings

  • A Cloud KMS key is a named object containing one or more key versions, along with metadata for the key.
  • A key exists on exactly one key ring tied to a specific location.
  • After creation, a key cannot be moved to another location or exported.

Google Cloud KMS Keys, Key Rings, and Key VersionsKey

  • A named object representing a cryptographic key that is used for a specific purpose. The key material – the actual bits used for cryptographic operations – can change over time as new key versions are created
  • Key is the most important object for understanding KMS usage.
  • Key purpose and other attributes of the key are connected with and managed using the key.
  • IAM permissions and roles can be used to allow and deny access to keys
  • Cloud KMS supports both asymmetric keys and symmetric keys.
    • Symmetric key
      • is used for symmetric encryption to protect some corpus of data for e.g., using AES-256 to encrypt a block of plaintext.
    • Asymmetric key
      • consists of a public and private key.
      • can be used for asymmetric encryption, or for creating digital signatures.
  • Key’s type (symmetric or asymmetric) can’t be changed after key creation

Key Ring

  • A grouping of keys for organizational purposes.
  • Key ring belongs to Google Cloud project and resides in a specific location
  • Keys inherit IAM policies from the Key Ring that contains them.
  • Grouping keys with related permissions in a key ring allows you to grant, revoke, or modify permissions to those keys at the key ring level without needing to act on each key individually.
  • Key rings provide convenience and categorization
  • To prevent resource name collisions, a key ring cannot be deleted.
  • Key rings and keys do not have billable costs or quota limitations, so their continued existence does not affect costs or production limits.

Key Metadata

  • Includes resource names, properties of KMS resources such as IAM policies, key type, key size, key state, and any other derived data
  • Key metadata can be managed differently than the key material.

Key Version

  • Represents the key material associated with a key at some point in time.
  • Key version is the resource that contains the actual key material.
  • Granting access to a key also grants access to all of its enabled versions. Access to a key version cannot be managed.
  • A key version can be disabled or destroyed without affecting other versions
  • Disabling or destroying a key also disables or destroys each key version.
  • Versions are numbered sequentially, beginning with version 1.
  • When a key is rotated, a new key version is created with new key material.
  • The same logical key can have multiple versions over time, thus limiting the use of any single version.
  • Symmetric keys will always have a primary version. This version is used for encrypting by default, if not version is specified
  • Asymmetric keys do not have primary versions, and a version must be specified when using the key.
  • When Cloud KMS performs decryption using symmetric keys, it identifies automatically which key version is needed to perform the decryption.

Key States

  • A key version’s state is always one of the following:
    • Pending generation (PENDING_GENERATION)
      • Applies to asymmetric keys only
      • is still being generated and can’t be used, enabled, disabled, or destroyed yet.
      • KMS will automatically change the state to enabled as soon as the version is ready.
    • Enabled (ENABLED)
      • is ready for use.
    • Disabled (DISABLED)
      • may not be used, but the key material is still available, and the version can be placed back into the enabled state.
    • Scheduled for destruction (DESTROY_SCHEDULED):
      • is scheduled for destruction, and will be destroyed soon.
      • can be placed back into the disabled state.
    • Destroyed (DESTROYED)
      • is destroyed, and the key material is no longer stored in Cloud KMS.
      • If the key version was used
        • for asymmetric or symmetric encryption, any ciphertext encrypted with this version is not recoverable.
        • for digital signing, new signatures cannot be created.
      • may not leave the destroyed state once entered.
  • A key version can only be used when it is enabled.

Google Cloud KMS Key States

Key Rotation

  • For symmetric encryption, periodically and automatically rotating keys is a recommended security practice
  • Cloud MS does not support automatic rotation of asymmetric keys and has to be done manually
  • With key rotation, data encrypted with previous key versions is not automatically re-encrypted with the new key version.
  • Rotating keys provides several benefits:
    • Limiting the number of messages encrypted with the same key version helps prevent brute-force attacks enabled by cryptanalysis.
    • In the event that a key is compromised, regular rotation limits the number of actual messages vulnerable to compromise.
    • If you suspect that a key version is compromised, disable it and revoke access to it as soon as possible.
    • Regular key rotation helps validate the key rotation procedures before a real-life security incident occurs.
    • Regular key rotation ensures that the system is resilient to manual rotation, whether due to a security breach or the need to migrate your application to a stronger cryptographic algorithm.

Key Hierarchy

Google Cloud KMS Key Hierarchy

  • Data Encryption Key (DEK)
    • A key used to encrypt data.
  • Key Encryption Key (KEK)
    • A key used to encrypt, or wrap, a DEK.
    • All Cloud KMS platform options (software, hardware, and external backends) allow you to control KEK.
  • KMS Master Key
    • The key used to encrypt the KEK.
    • This key is distributed in memory.
    • KMS Master Key is backed up on hardware devices.
  • Root KMS
    • Google’s internal key management service.

Cloud KMS Locations

  • Within a project, Cloud KMS resources can be created in one of many locations.
  • A key’s location impacts the performance of applications using the key
  • Regional
    • data centers exist in a specific geographical place
  • Dual-regional
    • data centers exist in two specific geographical places.
  • Multi-regional
    • data centers are spread across a general geographical area
  • Global
    • special multi-region with its data centers spread throughout the world
  • Reading and writing resources or associated metadata in dual-regional or multi-regional locations, including the global location may be slower than reading or writing from a single region.

GCP Certification Exam Practice Questions

  • Questions are collected from Internet and the answers are marked as per my knowledge and understanding (which might differ with yours).
  • GCP services are updated everyday and both the answers and questions might be outdated soon, so research accordingly.
  • GCP exam questions are not updated to keep up the pace with GCP updates, so even if the underlying feature has changed the question might not be updated
  • Open to further feedback, discussion and correction.

References

Google_Cloud_Key_Management_Service_KMS

Google Cloud Data Encryption

Google Cloud Data Encryption

  • Encryption is a process that takes legible data as input (often called plaintext) and transforms it into an output (often called ciphertext) that reveals little or no information about the plaintext
  • Encryption can be used to protect data in three states:
    • Encryption at Rest protects the data from a system compromise or data exfiltration by encrypting data while stored.
    • Encryption in Transit: protects the data if communications are intercepted while data moves between the site and the cloud provider or between two services.
    • Encryption in Use: protects the data when it is being used by servers to run computations, e.g. homomorphic encryption.

Encryption at Rest

  • Google uses several layers of encryption to protect customer data at rest.
  • All customer content stored at rest is encrypted, without any action required from the customer, using one or more encryption mechanisms.
  • All data stored in Google Cloud is encrypted at the storage level using AES256
  • Google encrypts data prior to it being written to disk.

Google Cloud Encryption At Rest Options

Google Cloud Default Encryption

  • Data for storage is split into chunks
  • Each chunk is encrypted with a unique Data Encryption Key (DEK)
  • Two chunks will not have the same encryption key, even if they are part of the same Cloud Storage object, owned by the same customer, or stored on the same machine
  • If a chunk of data is updated, it is encrypted with a new key, rather than by reusing the existing key
  • Data encryption keys are stored with the data because of the high volume of keys at Google, and the need for low latency and high availability
  • Backups are encrypted using a separate DEK
  • Data encryption keys are encrypted with (“wrapped” by) Key Encryption Keys (KEK) also referred to as Envelope Encryption
  • KEKs are stored centrally inside Google’s Key Management Service (KMS)
  • Having a smaller number of KEKs than DEKs and using a central KMS makes storing and encrypting data at Google scale manageable, and allows us to track and control data access from a central point.
  • KEKs are not exportable from Google’s KMS by design; all encryption and decryption with these keys must be done within KMS
  • KMS can automatically rotate KEKs at regular time intervals
  • KMS maintains an active key with a set of historical keys for decryption
  • Google uses a common cryptographic library, Tink, which incorporates the FIPS 140–2 validated module, BoringCrypto, to implement encryption consistently across almost all Google Cloud products.

Google Cloud Default Data Encryption

Google Cloud Default Decryption

  • Service makes a call to the storage system for the data it needs.
  • The storage system identifies the chunks in which that data is stored (the chunk IDs) and where they are stored.
  • For each chunk, the storage system pulls the wrapped DEK stored with that chunk and sends it to KMS for unwrapping.
  • The storage system verifies that the identified job is allowed to access that data chunk based on a job identifier, and using the chunk ID
  • KMS verifies that the storage system is authorized both to use the KEK associated with the service and to unwrap that specific DEK.
  • KMS passes the unwrapped DEK back to the storage system, which decrypts the data chunk and passes it to the service.

Google Cloud Decryption

Cloud Key Management Service – KMS

  • Cloud KMS help centralized management of encryption keys
  • Google’s Key Management Service is redundant and globally distributed.
  • Cloud KMS allows the customer to manage the encryption keys  (CMEK)
  • A CMEK or Customer Managed Encryption Key can be used in both server-side encryption (SSE) and client-side encryption (CSE).
  • CMEK key can be used with KMS encrypt/decrypt and also be attached to a bucket, GCE disk, etc.
  • CMEK supports importing your own key material, which is useful for migrations.

Customer Supplied Encryption Keys – CSEKs

  • Customer-Supplied Encryption Keys (CSEK) allows you to supply your own encryption keys, Google uses the key to protect the Google-generated keys used to encrypt and decrypt your data.
  • CSEK support only Google Cloud Storage and Google Compute Engine.
  • CSEK Encryption
    • User provides a raw CSEK as part of an API call.
    • The key is transmitted from the Google front end to the storage system’s memory
    • This key is used as the Key Encryption Key (KEK) in Google Cloud Storage for the data.
  • CSEK Decryption
    • Raw CSEK is used to unwrap wrapped chunk keys, to create raw chunk keys in memory.
    • These are used to decrypt data chunks stored in the storage systems.
    • These keys are used as the data encryption keys (DEK) in Google Cloud Storage for your data.
  • Raw CSEKCSEK-derived keys, and raw chunk/disk keys are never stored on disk unencrypted.
  • Raw chunk/disk keys are stored wrapped with CSEK-derived keys, and with Google keys where automatic restart is used. Google does not permanently store your keys on its servers.

Google Cloud Encryption At Rest Decision Tree

Encryption in Transit

  • Google applies several security measures to help ensure the authenticity, integrity, and privacy of data in transit.
    • Authentication: data source verification, either a human or a process, and destination.
    • Integrity: ensures data sent arrives at its destination unaltered.
    • Encryption: ensures data is unintelligible to keep it private.
  • Data in transit inside a physical boundary controlled by or on behalf of Google is generally authenticated but not necessarily encrypted.
  • Data is encrypted and authenticated in transit at one or more network layers when it moves outside physical boundaries not controlled by Google or on behalf of Google.
  • Depending on the connection that is being made, Google applies default protections to data in transit for e.g, communications are secured between the user and the Google Front End (GFE) using TLS.
  • Google Cloud customers with additional requirements for encryption of data over WAN can choose to implement further protections for data as it moves from a user to an application or VM to VM. These protections include IPSec tunnels, Gmail S/MIME, managed SSL certificates, and Istio.

Google Cloud Encryption In Transit

  • [Connection A] – User to Google Front End
    • Google accepts requests from around the world using a globally distributed system called the Google Front End (GFE)
    • GFE terminates traffic for incoming HTTP(S), TCP, and TLS proxy traffic, provides DDoS attack countermeasures, and routes and load balances traffic to the Google Cloud services themselves.
    • User requests to customer applications can be routed through a Google Cloud HTTP(S) or TCP/SSL Proxy Load Balancer external load balancer
    • Google automatically encrypts traffic between GFEs and the backends load balancers that reside within VPC networks
  • [Connection B] – User to customer application hosted on Google Cloud
    • Cloud VPN or Interconnect can help secure a direct connection to a VM using an external IP or network load balancer IP. As the connection does not go through GFE, it’s not encrypted by default.
  • [Connection C] – Virtual Machine to Virtual Machine
    • VM to VM connections is encrypted if they leave a physical boundary, and are authenticated within the physical boundary.
    • VM to VM traffic, using external IP addresses, is not encrypted by default, and its security is provided at the user’s discretion
  • [Connection D] – Virtual Machine to Google Cloud Service
    • Connectivity to Google APIs and services can be protected using private google access or private service access
    • From the VM to the GFE, Google Cloud services support protecting these connections with TLS by default
  • [Connection E] – Google Cloud Service to Google Cloud Service
    • Routing from one Google service to another takes place on Google Cloud network backbone and may require routing traffic outside of physical boundaries controlled by or on behalf of Google
    • Connections between these services are encrypted if they leave a physical boundary, and authenticated within the physical boundary.

GCP Certification Exam Practice Questions

  • Questions are collected from Internet and the answers are marked as per my knowledge and understanding (which might differ with yours).
  • GCP services are updated everyday and both the answers and questions might be outdated soon, so research accordingly.
  • GCP exam questions are not updated to keep up the pace with GCP updates, so even if the underlying feature has changed the question might not be updated
  • Open to further feedback, discussion and correction.

References

AWS Key Management Service – KMS – Overview

AWS Key Management Service – KMS

  • AWS KMS is a managed encryption service that allows creation and control of encryption keys to enable encryption of data easily
  • KMS provides a highly available key storage, management, and auditing solution to encrypt the data across AWS services & within applications
  • Customer master keys (CMK) are protected by hardware security modules (HSMs) that are validated by the FIPS 140-2 Cryptographic Module Validation Program
  • KMS is seamlessly integrated with several AWS services to make encrypting data in those service easy
  • KMS is also integrated with AWS CloudTrail to provide encryption key usage logs to help meet auditing, regulatory and compliance needs.
  • KMS Keys are only stored and used in the region in which they are created. They cannot be transferred to another region
  • KMS enforces usage and management policies, to control which IAM user, role from the account or other accounts who can manage and use keys
  • KMS supports
    • Encrypt, decrypt, and re-encrypt data
    • Generate data encryption keys that can be exported from the service in plaintext or encrypted under a master key that doesn’t leave the service
    • Generate random numbers suitable for cryptographic applications

Envelope encryption

  • AWS cloud services integrated with AWS KMS use a method called envelope encryption to protect the data.
  • Envelope encryption is an optimized method for encrypting data that uses two different keys (Master key and Data key)
  • With Envelop encryption
    • A data key is generated and used by the AWS service to encrypt each piece of data or resource.
    • Data key is encrypted under a master key defined in AWS KMS.
    • Encrypted data key is then stored by the AWS service.
    • For data decryption by the AWS service, the encrypted data key is passed to AWS KMS and decrypted under the master key that was originally encrypted under so the service can then decrypt the data.
  • KMS does support sending data less than 4 KB to be encrypted, envelope encryption can offer significant performance benefits
  • When the data is encrypted directly with KMS it must be transferred over the network.
  • Envelope encryption reduces the network load for the application or AWS cloud service as Only the request and fulfillment of the data key through KMS must go over the network

KMS Service Concepts

  • Customer Master Keys (CMKs)
    • AWS KMS customer master keys (CMKs) are 256-bit Advanced Encryption Standard (AES) symmetric keys that are not exportable.
    • CMKs are created in AWS KMS and never leave AWS KMS unencrypted.
    • CMK to encrypt and decrypt up to 4 KB (4096 bytes) of data
    • CMKs to generate, encrypt, and decrypt the data keys that are used outside of AWS KMS to encrypt the data [Envelope Encryption]
  • Key Material
    • CMK is a logical representation of a master key in AWS KMS.
    • CMK contains the key material used to encrypt and decrypt data.
    • CMK also includes master key’s identifiers and other metadata including its creation date, description, and key state,
    • By default AWS KMS generates the key material for a newly created CMK. But a CMK can be created without key material and then import your own key material into that CMK.
  • Data Keys
    • Data keys are encryption keys that you can use to encrypt data, including large amounts of data and other data encryption keys.
    • AWS KMS does not store, manage, or track your data keys.
    • Data keys must be used by services outside of AWS KMS.
  • Encryption & Decryption Process
    • Use KMS to get encrypted and plaintext data key using CMK
    • Use the plaintext data key to encrypt the data and store the encrypted data key with the data.
    • Use KMS decrypt to get the plaintext data key and decrypt the data
    • Remove the plaintext data key from memory, once operation completed.
  • Key Policies
    • help determine who can use and manage that CMK
    • add, remove, or change permissions at any time for a customer managed CMK,
    • cannot edit the key policy for an AWS managed CMK
  • Grants
    • provides permissions, an alternative to the key policy.
    • helps to give long-term access that allows AWS principals to use the customer managed CMKs
    • permissions specified in the grant might not take effect immediately due to eventual consistency
  • Grant Tokens
    • help mitigate the potential delay with grant
    • use the grant token received in the response to CreateGrant API request to make the permissions in the grant take effect immediately

KMS Working

  • KMS centrally manages and securely stores the keys
  • Keys can be generated or imported from the key management infrastructure
  • Keys can be used from within the applications and supported AWS services to protect the data, but the key never leaves KMS AWS.
  • Data is submitted to AWS KMS to be encrypted, or decrypted, under keys that you control.
  • Usage policies on these keys can be set that determine which users can use them to encrypt and decrypt data.

KMS Access Control

  • Primary way to manage access to AWS KMS CMKs is with policies.
  • AWS KMS required you attach resource-based policies to the customer master keys (CMKs), called key policies
  • All KMS CMKs have a key policy
  • KMS CMKs access can be controlled using
    • Use the key policy – use the key policy to control access to a CMK.
    • Use IAM policies with the key policy – use IAM policies in combination with the key policy to control access to a CMK. Controlling access this way enables you to manage all of the permissions for your IAM identities in IAM.
    • Use grants in combination with the key policy – use grants in combination with the key policy to allow access to a CMK. Controlling access this way enables you to allow access to the CMK in the key policy, and to allow users to delegate their access to others.
  • To allow access to a KMS CMK, key policy MUST be used, either alone or in combination with IAM policies or grants. IAM policies by themselves are not sufficient to allow access to a CMK, though they can be used in combination with a CMK’s key policy.

Rotating Customer Master Keys

  • AWS KMS managed CMK
    • automatically rotated every 3 years
  • CMKs with generated key material
    • supports automatic key rotation
    • keys are rotated every year
  • CMKs with imported key material or keys generated in an CloudHSM cluster using the KMS custom key store feature
    • do not support automatic key rotation
    • provides flexibility to manual rotate keys as required
  • for keys rotated automatically by KMS, data does not need to be re-encrypted. KMS keeps previous versions of keys to use for decryption of data encrypted under an old version of a key. All new encryption requests against a key in AWS KMS are encrypted under the newest version of the key.
  • For manually rotated keys, data has to be re-encrypted depending on the application’s configuration

KMS Features

  • Create keys with a unique alias and description
  • Import your own keys
  • Control which IAM users and roles can manage keys
  • Control which IAM users and roles can use keys to encrypt & decrypt data
  • Choose to have AWS KMS automatically rotate keys on an annual basis
  • Temporarily disable keys so they cannot be used by anyone
  • Re-enable disabled keys
  • Delete keys that you no longer use
  • Audit use of keys by inspecting logs in AWS CloudTrail

AWS Certification Exam Practice Questions

  • Questions are collected from Internet and the answers are marked as per my knowledge and understanding (which might differ with yours).
  • AWS services are updated everyday and both the answers and questions might be outdated soon, so research accordingly.
  • AWS exam questions are not updated to keep up the pace with AWS updates, so even if the underlying feature has changed the question might not be updated
  • Open to further feedback, discussion and correction.
  1. You are designing a personal document-archiving solution for your global enterprise with thousands of employee. Each employee has potentially gigabytes of data to be backed up in this archiving solution. The solution will be exposed to he employees as an application, where they can just drag and drop their files to the archiving system. Employees can retrieve their archives through a web interface. The corporate network has high bandwidth AWS DirectConnect connectivity to AWS. You have regulatory requirements that all data needs to be encrypted before being uploaded to the cloud. How do you implement this in a highly available and cost efficient way?
    1. Manage encryption keys on-premise in an encrypted relational database. Set up an on-premises server with sufficient storage to temporarily store files and then upload them to Amazon S3, providing a client-side master key. (Storing temporary increases cost and not a high availability option)
    2. Manage encryption keys in a Hardware Security Module (HSM) appliance on-premise server with sufficient storage to temporarily store, encrypt, and upload files directly into amazon Glacier. (Not cost effective)
    3. Manage encryption keys in amazon Key Management Service (KMS), upload to amazon simple storage service (s3) with client-side encryption using a KMS customer master key ID and configure Amazon S3 lifecycle policies to store each object using the amazon glacier storage tier. (With CSE-KMS the encryption happens at client side before the object is upload to S3 and KMS is cost effective as well)
    4. Manage encryption keys in an AWS CloudHSM appliance. Encrypt files prior to uploading on the employee desktop and then upload directly into amazon glacier (Not cost effective)
  2. An AWS customer is deploying an application that is composed of an Auto Scaling group of EC2 Instances. The customers security policy requires that every outbound connection from these instances to any other service within the customers Virtual Private Cloud must be authenticated using a unique x 509 certificate that contains the specific instance-id. In addition an x 509 certificates must be designed by the customer’s Key management service in order to be trusted for authentication.
    Which of the following configurations will support these requirements?
    1. Configure an IAM Role that grants access to an Amazon S3 object containing a signed certificate and configure the Auto Scaling group to launch instances with this role. Have the instances bootstrap get the certificate from Amazon S3 upon first boot.
    2. Embed a certificate into the Amazon Machine Image that is used by the Auto Scaling group Have the launched instances generate a certificate signature request with the instance’s assigned instance-id to the Key management service for signature.
    3. Configure the Auto Scaling group to send an SNS notification of the launch of a new instance to the trusted key management service. Have the Key management service generate a signed certificate and send it directly to the newly launched instance.
    4. Configure the launched instances to generate a new certificate upon first boot. Have the Key management service poll the AutoScaling group for associated instances and send new instances a certificate signature that contains the specific instance-id.
  3. A company has a customer master key (CMK) with imported key materials. Company policy requires that all encryption keys must be rotated every year. What can be done to implement the above policy?
    1. Enable automatic key rotation annually for the CMK.
    2. Use AWS Command Line interface to create an AWS Lambda function to rotate the existing CMK annually.
    3. Import new key material to the existing CMK and manually rotate the CMK.
    4. Create a new CMK, import new key material to it, and point the key alias to the new CMK.
  4. An organization policy states that all encryption keys must be automatically rotated every 12 months. Which AWS Key Management Service (KMS) key type should be used to meet this requirement?
    1. AWS managed Customer Master Key (CMK)
    2. Customer managed CMK with AWS generated key material
    3. Customer managed CMK with imported key material
    4. AWS managed data key

AWS S3 Data Protection

AWS S3 Data Protection

  • Amazon S3 provides a S3 data protection using highly durable storage infrastructure designed for mission-critical and primary data storage.
  • Objects are redundantly stored on multiple devices across multiple facilities in an S3 region.
  • S3 PUT and PUT Object copy operations synchronously store the data across multiple facilities before returning SUCCESS.
  • Once the objects are stored, S3 maintains its durability by quickly detecting and repairing any lost redundancy.
  • S3 also regularly verifies the integrity of data stored using checksums. If  S3 detects data corruption, it is repaired using redundant data.
  • In addition, S3 calculates checksums on all network traffic to detect corruption of data packets when storing or retrieving data
  • Data protection against accidental overwrites and deletions can be added by enabling Versioning to preserve, retrieve and restore every version of the object stored
  • S3 also provides the ability to protect data in-transit (as it travels to and from S3) and at rest (while it is stored in S3)

S3 Data Protection

Data in-transit

  • S3 allows protection of data in-transit by enabling communication via SSL or using client-side encryption

Data at Rest

  • S3 supports both client side encryption and server side encryption for protecting data at rest
  • Using Server-Side Encryption, S3 encrypts the object before saving it on disks in its data centers and decrypt it when the objects are downloaded
  • Using Client-Side Encryption, data is encrypted at client-side and uploaded to S3. In this case, the encryption process, the encryption keys, and related tools are managed by the user.

Server-Side Encryption

  • Server-side encryption is about data encryption at rest
  • Server-side encryption encrypts only the object data. Any object metadata is not encrypted.
  • S3 handles the encryption (as it writes to disks) and decryption (when objects are accessed) of the data objects
  • There is no difference in the access mechanism for both encrypted or unencrypted objects and is handled transparently by S3

Server-Side Encryption with S3-Managed Keys (SSE-S3)

  • Each object is encrypted with a unique data key employing strong multi-factor encryption.
  • SSE-S3 encrypts the data key with a master key that is regularly rotated.
  • S3 server-side encryption uses one of the strongest block ciphers available, 256-bit Advanced Encryption Standard (AES-256), to encrypt the data.
  • Whether or not objects are encrypted with SSE-S3 can’t be enforced when they are uploaded using pre-signed URLs, because the only way server-side encryption can be specified is through the AWS Management Console or through an HTTP request header

Server-Side Encryption with AWS KMS-Managed Keys (SSE-KMS)

Server-Side Encryption with AWS KMS-Managed Keys (SSE-KMS)

  • SSE-KMS is similar to SSE-S3, but it uses AWS Key management Services (KMS) which provides additional benefits along with additional charges
    • KMS is a service that combines secure, highly available hardware and software to provide a key management system scaled for the cloud.
    • KMS uses customer master keys (CMKs) to encrypt the S3 objects.
    • Master key is never made available
    • KMS enables you to centrally create encryption keys, define the policies that control how keys can be used
    • Allows audit use of key usage to prove they are being used correctly, by inspecting logs in AWS CloudTrail
    • Allows keys to temporarily disabled and re-enabled
    • Allows keys to be rotated regularly
    • Security controls in AWS KMS can help meet encryption-related compliance requirements.
  • SSE-KMS enables separate permissions for the use of an envelope key (that is, a key that protects the data’s encryption key) that provides added protection against unauthorized access of the objects in S3.
  • SSE-KMS provides the option to create and manage encryption keys yourself, or use a default customer master key (CMK) that is unique to you, the service you’re using, and the region you’re working in.
  • Creating and Managing CMK gives more flexibility, including the ability to create, rotate, disable, and define access controls, and to audit the encryption keys used to protect the data.
  • Data keys used to encrypt your data are also encrypted and stored alongside the data they protect and are unique to each object
  • Process flow
    • An application or AWS service client requests an encryption key to encrypt data and passes a reference to a master key under the account.
    • Client requests are authenticated based on whether they have access to use the master key.
    • A new data encryption key is created, and a copy of it is encrypted under the master key.
    • Both the data key and encrypted data key are returned to the client.
    • Data key is used to encrypt customer data and then deleted as soon as is practical.
    • Encrypted data key is stored for later use and sent back to AWS KMS when the source data needs to be decrypted.

Server-Side Encryption with Customer-Provided Keys (SSE-C)

AWS S3 Server Side Encryption using Customer Provided Keys SSE-C

  • Encryption keys can be managed and provided by the Customer and S3 manages the encryption, as it writes to disks, and decryption, when you access the objects
  • When you upload an object, the encryption key is provided as a part of the request and S3 uses that encryption key to apply AES-256 encryption to the data and removes the encryption key from memory.
  • When you download an object, the same encryption key should be provided as a part of the request. S3 first verifies the encryption key and if matches decrypts the object before returning back to you
  • As each object and each object’s version can be encrypted with a different key, you are responsible for maintaining the mapping between the object and the encryption key used.
  • SSE-C request must be done through HTTPS and S3 will reject any requests made over HTTP when using SSE-C.
  • For security considerations, AWS recommends to consider any key sent erroneously using HTTP to be compromised and discarded or rotated
  • S3 does not store the encryption key provided. Instead, it stores a randomly salted HMAC value of the encryption key which can be used to validate future requests. The salted HMAC value cannot be used to derive the value of the encryption key or to decrypt the contents of the encrypted object. That means, if you lose the encryption key, you lose the object.

Client-Side Encryption

Client-side encryption refers to encrypting data before sending it to Amazon S3 and decrypting the data after downloading it

AWS KMS-managed Customer Master Key (CMK)

  • Customer can maintain the encryption CMK with AWS KMS and can provide the CMK id to the client to encrypt the data
  • Uploading Object
    • AWS S3 encryption client first sends a request to AWS KMS for the key to encrypt the object data
    • AWS KMS returns a randomly generated data encryption key with 2 versions a plain text version for encrypting the data and cipher blob to be uploaded with the object as object metadata
    • Client obtains a unique data encryption key for each object it uploads.
    • AWS S3 encryption client uploads the encrypted data and the cipher blob with object metadata
  • Download Object
    • AWS Client first downloads the encrypted object from S3 along with the cipher blob version of the data encryption key stored as object metadata
    • AWS Client then sends the cipher blob to AWS KMS to get the plain text version of the same, so that it can decrypt the object data.

Client-Side master key

  • Encryption master keys are completely maintained at Client-side
  • Uploading Object
    • S3 encryption client ( for e.g. AmazonS3EncryptionClient in the AWS SDK for Java) locally generates randomly a one-time-use symmetric key (also known as a data encryption key or data key).
    • Client encrypts the data encryption key using the customer provided master key
    • Client uses this data encryption key to encrypt the data of a single S3 object (for each object, the client generates a separate data key).
    • Client then uploads the encrypted data to Amazon S3 and also saves the encrypted data key and its material description  as object metadata (x-amz-meta-x-amz-key) in Amazon S3 by default
  • Downloading Object
    • Client first downloads the encrypted object from Amazon S3 along with the object metadata.
    • Using the material description in the metadata, the client first determines which master key to use to decrypt the encrypted data key.
    • Using that master key, the client decrypts the data key and uses it to decrypt the object
  • Client-side master keys and your unencrypted data are never sent to AWS
  • If the master key is lost the data cannot be decrypted

AWS Certification Exam Practice Questions

  • Questions are collected from Internet and the answers are marked as per my knowledge and understanding (which might differ with yours).
  • AWS services are updated everyday and both the answers and questions might be outdated soon, so research accordingly.
  • AWS exam questions are not updated to keep up the pace with AWS updates, so even if the underlying feature has changed the question might not be updated
  • Open to further feedback, discussion and correction.
  1. A company is storing data on Amazon Simple Storage Service (S3). The company’s security policy mandates that data is encrypted at rest. Which of the following methods can achieve this? Choose 3 answers
    1. Use Amazon S3 server-side encryption with AWS Key Management Service managed keys
    2. Use Amazon S3 server-side encryption with customer-provided keys
    3. Use Amazon S3 server-side encryption with EC2 key pair.
    4. Use Amazon S3 bucket policies to restrict access to the data at rest.
    5. Encrypt the data on the client-side before ingesting to Amazon S3 using their own master key
    6. Use SSL to encrypt the data while in transit to Amazon S3.
  2. A user has enabled versioning on an S3 bucket. The user is using server side encryption for data at Rest. If the user is supplying his own keys for encryption (SSE-C) which of the below mentioned statements is true?
    1. The user should use the same encryption key for all versions of the same object
    2. It is possible to have different encryption keys for different versions of the same object
    3. AWS S3 does not allow the user to upload his own keys for server side encryption
    4. The SSE-C does not work when versioning is enabled
  3. A storage admin wants to encrypt all the objects stored in S3 using server side encryption. The user does not want to use the AES 256 encryption key provided by S3. How can the user achieve this?
    1. The admin should upload his secret key to the AWS console and let S3 decrypt the objects
    2. The admin should use CLI or API to upload the encryption key to the S3 bucket. When making a call to the S3 API mention the encryption key URL in each request
    3. S3 does not support client supplied encryption keys for server side encryption
    4. The admin should send the keys and encryption algorithm with each API call
  4. A user has enabled versioning on an S3 bucket. The user is using server side encryption for data at rest. If the user is supplying his own keys for encryption (SSE-C), what is recommended to the user for the purpose of security?
    1. User should not use his own security key as it is not secure
    2. Configure S3 to rotate the user’s encryption key at regular intervals
    3. Configure S3 to store the user’s keys securely with SSL
    4. Keep rotating the encryption key manually at the client side
  5. A system admin is planning to encrypt all objects being uploaded to S3 from an application. The system admin does not want to implement his own encryption algorithm; instead he is planning to use server side encryption by supplying his own key (SSE-C.. Which parameter is not required while making a call for SSE-C?
    1. x-amz-server-side-encryption-customer-key-AES-256
    2. x-amz-server-side-encryption-customer-key
    3. x-amz-server-side-encryption-customer-algorithm
    4. x-amz-server-side-encryption-customer-key-MD5
  6. A customer is leveraging Amazon Simple Storage Service in eu-west-1 to store static content for a web-based property. The customer is storing objects using the Standard Storage class. Where are the customers objects replicated?
    1. A single facility in eu-west-1 and a single facility in eu-central-1
    2. A single facility in eu-west-1 and a single facility in us-east-1
    3. Multiple facilities in eu-west-1
    4. A single facility in eu-west-1
  7. You are designing a personal document-archiving solution for your global enterprise with thousands of employee. Each employee has potentially gigabytes of data to be backed up in this archiving solution. The solution will be exposed to he employees as an application, where they can just drag and drop their files to the archiving system. Employees can retrieve their archives through a web interface. The corporate network has high bandwidth AWS DirectConnect connectivity to AWS. You have regulatory requirements that all data needs to be encrypted before being uploaded to the cloud. How do you implement this in a highly available and cost efficient way?
    1. Manage encryption keys on-premise in an encrypted relational database. Set up an on-premises server with sufficient storage to temporarily store files and then upload them to Amazon S3, providing a client-side master key. (Storing temporary increases cost and not a high availability option)
    2. Manage encryption keys in a Hardware Security Module(HSM) appliance on-premise server with sufficient storage to temporarily store, encrypt, and upload files directly into amazon Glacier. (Not cost effective)
    3. Manage encryption keys in amazon Key Management Service (KMS), upload to amazon simple storage service (s3) with client-side encryption using a KMS customer master key ID and configure Amazon S3 lifecycle policies to store each object using the amazon glacier storage tier. (with CSE-KMS the encryption happens at client side before the object is upload to S3 and KMS is cost effective as well)
    4. Manage encryption keys in an AWS CloudHSM appliance. Encrypt files prior to uploading on the employee desktop and then upload directly into amazon glacier (Not cost effective)
  8. A user has enabled server side encryption with S3. The user downloads the encrypted object from S3. How can the user decrypt it?
    1. S3 does not support server side encryption
    2. S3 provides a server side key to decrypt the object
    3. The user needs to decrypt the object using their own private key
    4. S3 manages encryption and decryption automatically
  9. When uploading an object, what request header can be explicitly specified in a request to Amazon S3 to encrypt object data when saved on the server side?
    1. x-amz-storage-class
    2. Content-MD5
    3. x-amz-security-token
    4. x-amz-server-side-encryption