Cross-account encryption access in AWS refers to the ability to share encrypted resources between different AWS accounts while maintaining security and proper access controls. This is particularly important when organizations need to collaborate across multiple accounts or when implementing a multi…Cross-account encryption access in AWS refers to the ability to share encrypted resources between different AWS accounts while maintaining security and proper access controls. This is particularly important when organizations need to collaborate across multiple accounts or when implementing a multi-account architecture strategy.
When working with AWS Key Management Service (KMS), cross-account access requires configuring both the KMS key policy and IAM policies in the target account. The KMS key policy must explicitly grant permissions to the external account's principals, allowing them to perform operations like Encrypt, Decrypt, GenerateDataKey, and DescribeKey.
For encrypted S3 buckets, cross-account access involves updating the bucket policy to allow the external account access, configuring the KMS key policy to permit the external account to use the encryption key, and ensuring the IAM user or role in the external account has appropriate permissions.
With encrypted EBS snapshots, sharing across accounts requires modifying the snapshot permissions to include the target account ID and granting KMS key access to the target account. The receiving account must have permissions to use the shared KMS key for decryption.
Key considerations for cross-account encryption access include using customer-managed KMS keys rather than AWS-managed keys since AWS-managed keys cannot be shared across accounts. Additionally, implementing the principle of least privilege ensures accounts only receive necessary permissions.
For encrypted RDS snapshots, you must first share the snapshot with the target account and then share the KMS key used for encryption. The target account can then copy the snapshot using their own KMS key.
Best practices include regularly auditing cross-account permissions, using AWS Organizations service control policies for additional governance, implementing CloudTrail logging to monitor key usage across accounts, and considering using AWS Resource Access Manager for simplified resource sharing where applicable.
Cross-Account Encryption Access
Why Cross-Account Encryption Access is Important
In modern cloud architectures, organizations frequently need to share encrypted resources across multiple AWS accounts. This is essential for scenarios like consolidated billing structures, development and production environment separation, or multi-team collaboration. Understanding how to properly configure cross-account access to encrypted resources is crucial for both security compliance and operational efficiency.
What is Cross-Account Encryption Access?
Cross-account encryption access refers to the ability to share AWS resources that are encrypted with AWS Key Management Service (KMS) keys across different AWS accounts. When resources like S3 objects, EBS snapshots, RDS snapshots, or Lambda functions are encrypted, the consuming account must have appropriate permissions to both the resource AND the encryption key used to protect it.
How Cross-Account Encryption Access Works
There are two main components required for cross-account encrypted resource access:
1. Resource-Based Permissions: The resource itself (S3 bucket, snapshot, etc.) must have a policy allowing access from the target account.
2. KMS Key Policy Permissions: The KMS key used to encrypt the resource must have a key policy that grants the target account permissions to use the key for decryption operations.
Key Policy Configuration: The KMS key policy in the source account must include: - kms:Decrypt - Allows decryption of data - kms:DescribeKey - Allows viewing key metadata - kms:GenerateDataKey (if re-encryption is needed)
IAM Policy in Target Account: The IAM principal in the target account must have an IAM policy that allows it to use the KMS key in the source account via the key's ARN.
Common Use Cases: - Sharing encrypted S3 objects between accounts - Copying encrypted EBS snapshots across accounts - Sharing encrypted RDS snapshots - Cross-account access to encrypted SQS queues - Lambda functions accessing encrypted resources in other accounts
Important Considerations:
- AWS Managed Keys cannot be shared cross-account - You must use Customer Managed Keys (CMKs) for cross-account scenarios - Both key policy AND IAM policy must grant permissions for access to work - The KMS key and the resource must be in the same region for most services - Key grants can also be used as an alternative to key policies for temporary access
Exam Tips: Answering Questions on Cross-Account Encryption Access
1. Remember the Two-Part Requirement: When a question involves accessing encrypted resources across accounts, always consider that BOTH the resource policy AND the KMS key policy need to allow access. Missing either one results in access denied errors.
2. AWS Managed Keys vs Customer Managed Keys: If a scenario describes using AWS managed keys (aws/s3, aws/ebs, etc.) for cross-account access, this is a red flag. Cross-account access requires Customer Managed Keys.
3. Look for IAM Policy Requirements: The target account's IAM principal needs permissions to call KMS APIs on the source account's key. Questions may present scenarios where the key policy is correct but IAM permissions are missing.
4. Key Policy Principal Format: Cross-account key policies specify the target account or specific IAM principals using ARN format. Watch for questions testing correct ARN syntax.
5. Grants vs Policies: Grants provide temporary, programmatic access to KMS keys and are useful for cross-account scenarios where you need to delegate key usage. Key policies are for more permanent access patterns.
6. Error Scenarios: Questions describing AccessDenied errors when accessing encrypted cross-account resources are typically testing whether you understand that KMS permissions are separate from resource permissions.
7. Re-encryption Scenarios: When copying encrypted resources to another account, the target account may need to re-encrypt with their own key, requiring GenerateDataKey and Encrypt permissions.