Types Of Keys
Delmy Moonsommy
To help with string manipulation around template string literals, TypeScript includes a set of types which can be used in string manipulation within the type system. You can find those in the Template Literal Types documentation.
We use a key for defining various types of integrity constraints in a database. A table, on the other hand, represents a collection of the records of various events for any relation. Now, there might be thousands of these records, and some of these might even be duplicated.
The keys in DBMS can be a combination of multiple attributes (or columns), or they can be just one single attribute. The primary motive of the keys is to provide every record with a unique identity of its own.
A super key refers to the set of all those keys that help us uniquely identify all the rows present in a table. It means that all of these columns present in a table that can identify the columns of that table uniquely act as the super keys.
The candidate keys refer to those attributes that identify rows uniquely in a table. In a table, we select the primary key from a candidate key. Thus, a candidate key has similar properties as that of the primary keys that we have explained above. In a table, there can be multiple candidate keys.
As we have stated above, any table can consist of multiple choices for the primary key. But, it can only choose one. Thus, all those keys that did not become a primary key are known as alternate keys.
2. A relation X consists of eight attributes BADCFEHG. The fields of X consist of just atomic values. E = DG ? H, B ? AD, A ? DEG, F ? B, E ? FH refers to a set of FDs (functional dependencies) so that E+ is exactly the set of functional dependencies that hold for X. Here, the relation X consists of how many candidate keys?
AWS KMS keys (KMS keys) are the primary resource in AWS KMS. You can use a KMS key to encrypt, decrypt, and re-encrypt data. It can also generate data keys that you can use outside of AWS KMS. Typically, you'll use symmetric encryption KMS keys, but you can create and use asymmetric KMS keys for encryption or signing, and create and use HMAC KMS keys to generate and verify HMAC tags.
You can create a KMS key with cryptographic key material generated in AWS KMS FIPS validated hardware security modules. The key material for symmetric KMS keys and the private keys of asymmetric KMS key never leaves AWS KMS unencrypted. To use or manage your KMS keys, you must use AWS KMS. For information about creating and managing KMS keys, see Managing keys. For information about using KMS keys, see the AWS Key Management Service API Reference.
By default, AWS KMS creates the key material for a KMS key. You cannot extract, export, view, or manage this key material. The only exception is the public key of an asymmetric key pair, which you can export for use outside of AWS. Also, you cannot delete this key material; you must delete the KMS key. However, you can import your own key material into a KMS key, or use a custom key store to create KMS keys that use key material in your AWS CloudHSM cluster, or key material in an external key manager that you own and manage outside of AWS.
The KMS keys that you create are customer managed keys. AWS services that use KMS keys to encrypt your service resources often create keys for you. KMS keys that AWS services create in your AWS account are AWS managed keys. KMS keys that AWS services create in a service account are AWS owned keys.
AWS services that integrate with AWS KMS differ in their support for KMS keys. Some AWS services encrypt your data by default with an AWS owned key or an AWS managed key. Some AWS services support customer managed keys. Other AWS services support all types of KMS keys to allow you the ease of an AWS owned key, the visibility of an AWS managed key, or the control of a customer managed key. For detailed information about the encryption options that an AWS service offers, see the Encryption at Rest topic in the user guide or the developer guide for the service.
The KMS keys that you create are customer managed keys. Customer managed keys are KMS keys in your AWS account that you create, own, and manage. You have full control over these KMS keys, including establishing and maintaining their key policies, IAM policies, and grants, enabling and disabling them, rotating their cryptographic material, adding tags, creating aliases that refer to the KMS keys, and scheduling the KMS keys for deletion.
Customer managed keys appear on the Customer managed keys page of the AWS Management Console for AWS KMS. To definitively identify a customer managed key, use the DescribeKey operation. For customer managed keys, the value of the KeyManager field of the DescribeKey response is CUSTOMER.
Customer managed keys incur a monthly fee and a fee for use in excess of the free tier. They are counted against the AWS KMS quotas for your account. For details, see AWS Key Management Service Pricing and Quotas.
You have permission to view the AWS managed keys in your account, view their key policies, and audit their use in AWS CloudTrail logs. However, you cannot change any properties of AWS managed keys, rotate them, change their key policies, or schedule them for deletion. And, you cannot use AWS managed keys in cryptographic operations directly; the service that creates them uses them on your behalf.
AWS managed keys appear on the AWS managed keys page of the AWS Management Console for AWS KMS. You can also identify AWS managed keys by their aliases, which have the format aws/service-name, such as aws/redshift. To definitively identify an AWS managed keys, use the DescribeKey operation. For AWS managed keys, the value of the KeyManager field of the DescribeKey response is AWS.
There is no monthly fee for AWS managed keys. They can be subject to fees for use in excess of the free tier, but some AWS services cover these costs for you. For details, see the Encryption at Rest topic in the user guide or developer guide for the service. For details, see AWS Key Management Service Pricing.
AWS managed keys do not count against resource quotas on the number of KMS keys in each Region of your account. But when used on behalf of a principal in your account, the KMS keys count against request quotas. For details, see Quotas.
AWS owned keys are a collection of KMS keys that an AWS service owns and manages for use in multiple AWS accounts. Although AWS owned keys are not in your AWS account, an AWS service can use an AWS owned key to protect the resources in your account.
Some AWS services let you choose an AWS owned key or a customer managed key. In general, unless you are required to audit or control the encryption key that protects your resources, an AWS owned key is a good choice. AWS owned keys are completely free of charge (no monthly fees or usage fees), they do not count against the AWS KMS quotas for your account, and they're easy to use. You don't need to create or maintain the key or its key policy.
The rotation of AWS owned keys varies across services. For information about the rotation of a particular AWS owned key, see the Encryption at Rest topic in the user guide or developer guide for the service.
In AWS KMS, a symmetric encryption KMS key represents a 256-bit AES-GCM encryption key, except in China Regions, where it represents a 128-bit SM4 encryption key. Symmetric key material never leaves AWS KMS unencrypted. To use a symmetric encryption KMS key, you must call AWS KMS. Symmetric encryption keys are used in symmetric encryption, where the same key is used for encryption and decryption. Unless your task explicitly requires asymmetric encryption, symmetric encryption KMS keys, which never leave AWS KMS unencrypted, are a good choice.
AWS services that are integrated with AWS KMS use only symmetric encryption KMS keys to encrypt your data. These services do not support encryption with asymmetric KMS keys. For help determining whether a KMS key is symmetric or asymmetric, see Identifying asymmetric KMS keys.
You can use a symmetric encryption KMS key in AWS KMS to encrypt, decrypt, and re-encrypt data, and generate data keys and data key pairs. You can create multi-Region symmetric encryption KMS keys, import your own key material into a symmetric encryption KMS key, and create symmetric encryption KMS keys in custom key stores. For a table comparing the operations that you can perform on KMS keys of different types, see Key type reference.
You can create asymmetric KMS keys in AWS KMS. An asymmetric KMS key represents a mathematically related public key and private key pair. The private key never leaves AWS KMS unencrypted. To use the private key, you must call AWS KMS. You can use the public key within AWS KMS by calling the AWS KMS API operations, or you can download the public key and use it outside of AWS KMS. You can also create multi-Region asymmetric KMS keys.
You can create asymmetric KMS keys that represent RSA key pairs or SM2 key pairs (China Regions only) for public key encryption or signing and verification, or elliptic curve key pairs for signing and verification.
Data keys are symmetric keys you can use to encrypt data, including large amounts of data and other data encryption keys. Unlike symmetric KMS keys, which can't be downloaded, data keys are returned to you for use outside of AWS KMS.
When AWS KMS generates data keys, it returns a plaintext data key for immediate use (optional) and an encrypted copy of the data key that you can safely store with the data. When you are ready to decrypt the data, you first ask AWS KMS to decrypt the encrypted data key.
AWS KMS generates, encrypts, and decrypts data keys. However, AWS KMS does not store, manage, or track your data keys, or perform cryptographic operations with data keys. You must use and manage data keys outside of AWS KMS. For help using the data keys securely, see the AWS Encryption SDK.
This effect is particularly important for the many AWS services that use data keys to protect the resources that the service manages. The following example uses Amazon Elastic Block Store (Amazon EBS) and Amazon Elastic Compute Cloud (Amazon EC2). Different AWS services use data keys in different ways. For details, see the Data protection section of the Security chapter for the AWS service.
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