A protected object version can’t be overwritten or deleted by any user, including the root user in the AWS account.
Object retention mode can’t be changed, and its retention period can’t be shortened.
Object versions can’t be overwritten or deleted for the duration of the retention period.
S3 Access Points
S3 access points simplify data access for any AWS service or customer application that stores data in S3.
Access points are named network endpoints that are attached to buckets and can be used to perform S3 object operations, such as GetObject and PutObject.
Each access point has distinct permissions and network controls that S3 applies for any request that is made through that access point.
Each access point enforces a customized access point policy that works in conjunction with the bucket policy, attached to the underlying bucket.
An access point can be configured to accept requests only from a VPC to restrict S3 data access to a private network.
Custom block public access settings can be configured for each access point.
S3 VPC Gateway Endpoint
A VPC endpoint enables connections between a VPC and supported services, without requiring that you use an internet gateway, NAT device, VPN connection, or AWS Direct Connect connection.
VPC is not exposed to the public internet.
A Gateway Endpoint is a gateway that is a target for a route in your route table used for traffic destined to either S3.
S3 Block Public Access
S3 Block Public Access provides controls across an entire AWS Account or at the individual S3 bucket level to ensure that objects never have public access, now and in the future.
S3 Block Public Access provides settings for access points, buckets, and accounts to help manage public access to S3 resources.
By default, new buckets, access points, and objects don’t allow public access. However, users can modify bucket policies, access point policies, or object permissions to allow public access.
S3 Block Public Access settings override these policies and permissions so that public access to these resources can be limited.
S3 Block Public Access allows account administrators and bucket owners to easily set up centralized controls to limit public access to their S3 resources that are enforced regardless of how the resources are created.
S3 doesn’t support block public access settings on a per-object basis.
S3 Block Public Access settings when applied to an account apply to all AWS Regions globally.
S3 Access Analyzer
S3 Access Analyzer monitors the access policies, ensuring that the policies provide only the intended access to your S3 resources.
S3 Access Analyzer evaluates the bucket access policies and enables you to discover and swiftly remediate buckets with potentially unintended access.
S3 Security Best Practices
S3 Preventative Security Best Practices
Ensure S3 buckets use the correct policies and are not publicly accessible
Use S3 block public access
Identify Bucket policies and ACLs that allow public access
AWS S3 Encryption supports both data at rest and data in transit encryption.
S3 allows protection of data in transit by enabling communication via SSL or using client-side encryption
Data at Rest
S3 encrypts the object before saving it on disks in its data centers and decrypt it when the objects are downloaded
data is encrypted at the client-side and uploaded to S3.
the encryption process, the encryption keys, and related tools are managed by the user.
S3 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 and unencrypted objects and is handled transparently by S3
Server-Side Encryption with S3-Managed Keys – SSE-S3
Encryption keys are handled and managed by AWS
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.
Request must set header x-amz-server-side-encryption to AES-256
For enforcing server-side encryption for all of the objects that are stored in a bucket, use a bucket policy that denies permissions to upload an object unless the request includes x-amz-server-side-encryption header to request server-side encryption.
Server-Side Encryption with AWS KMS-Managed Keys – SSE-KMS
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.
The master key is never made available.
KMS enables you to centrally create encryption keys, and define the policies that control how keys can be used.
Allows audit of keys used to prove they are being used correctly, by inspecting logs in AWS CloudTrail.
Allows keys to be 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 to 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 audit the encryption keys used to protect the data.
Data keys used to encrypt the data are also encrypted and stored alongside the data they protect and are unique to each object.
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.
S3 only supports symmetric keys and not asymmetric keys.
Must set header x-amz-server-side-encryption to aws:kms
Server-Side Encryption with 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 it matches the object is decrypted 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 requests must be done through HTTPS and S3 will reject any requests made over HTTP when using SSE-C.
For security considerations, AWS recommends considering any key sent erroneously using HTTP to be compromised and it should be discarded or rotated.
S3 does not store the encryption key provided. Instead, a randomly salted HMAC value of the encryption key is stored which can be used to validate future requests. The salted HMAC value cannot be used to decrypt the contents of the encrypted object or to derive the value of the encryption key. That means, if you lose the encryption key, you lose the object.
Client-side encryption refers to encrypting data before sending it to 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
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 cypher 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
AWS Client first downloads the encrypted object 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 the Client-side
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 S3 and also saves the encrypted data key and its material description as object metadata ( x-amz-meta-x-amz-key) in S3 by default
Client first downloads the encrypted object from 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
Enforcing S3 Encryption
S3 Encryption in Transit
S3 Bucket Policy can be used to enforce SSL communication with S3 using the effect deny with condition aws:SecureTransport set to false.
S3 Default Encryption
helps set the default encryption behaviour for an S3 bucket so that all new objects are encrypted when they are stored in the bucket.
Objects are encrypted using SSE with either S3-managed keys (SSE-S3) or AWS KMS keys stored in AWS KMS (SSE-KMS).
S3 Bucket Policy
can be applied that denies permissions to upload an object unless the request includes x-amz-server-side-encryption header to request server-side encryption.
is not required, if S3 default encryption is enabled
are evaluated before the default encryption.
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.
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
Use Amazon S3 server-side encryption with AWS Key Management Service managed keys
Use Amazon S3 server-side encryption with customer-provided keys
Use Amazon S3 server-side encryption with EC2 key pair.
Use Amazon S3 bucket policies to restrict access to the data at rest.
Encrypt the data on the client-side before ingesting to Amazon S3 using their own master key
Use SSL to encrypt the data while in transit to Amazon S3.
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?
The user should use the same encryption key for all versions of the same object
It is possible to have different encryption keys for different versions of the same object
AWS S3 does not allow the user to upload his own keys for server side encryption
The SSE-C does not work when versioning is enabled
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?
The admin should upload his secret key to the AWS console and let S3 decrypt the objects
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
S3 does not support client supplied encryption keys for server side encryption
The admin should send the keys and encryption algorithm with each API call
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?
User should not use his own security key as it is not secure
Configure S3 to rotate the user’s encryption key at regular intervals
Configure S3 to store the user’s keys securely with SSL
Keep rotating the encryption key manually at the client side
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?
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?
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)
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)
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)
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)
A user has enabled server side encryption with S3. The user downloads the encrypted object from S3. How can the user decrypt it?
S3 does not support server side encryption
S3 provides a server side key to decrypt the object
The user needs to decrypt the object using their own private key
S3 manages encryption and decryption automatically
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?
A company must ensure that any objects uploaded to an S3 bucket are encrypted. Which of the following actions should the SysOps Administrator take to meet this requirement? (Select TWO.)
Implement AWS Shield to protect against unencrypted objects stored in S3 buckets.
Implement Object access control list (ACL) to deny unencrypted objects from being uploaded to the S3 bucket.
Implement Amazon S3 default encryption to make sure that any object being uploaded is encrypted before it is stored.
Implement Amazon Inspector to inspect objects uploaded to the S3 bucket to make sure that they are encrypted.
Implement S3 bucket policies to deny unencrypted objects from being uploaded to the buckets.