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Encryption is a process that takes plaintext as input and transforms it into an output (ciphertext) that reveals no information about the plaintext. Encryption adds a layer of defense for protecting data and ensures that if the data accidentally falls into an attacker’s hands, they cannot access the data without having access to the encryption keys. Even if an attacker obtains the storage devices containing your data, they will not be able to understand or decrypt it.

Data Encryption Options

Cloud storage encrypts data on the server-side before it is written to disk, at no additional charge. Besides this standard, there are additional ways to encrypt the data while using Cloud Storage.

Below are the available encryption options for Google Cloud:

Server-side encryption

Google Cloud Storage performs server-side encryption by default on all uploaded objects. All data is broken into chunks which can be up to several GB in size. Using envelope encryption, each chunk of data is encrypted with a unique Data Encryption Key (DEK) that is also encrypted with a Key Encryption Key (KEK). The encrypted version of the DEK is then stored alongside the encrypted data, and the encrypted chunks of data are distributed across Google’s storage systems

Google Cloud Storage supports server-side encryption with two key options:
Customer-supplied encryption keys

With the customer-supplied encryption key (CSEK) option, users must generate their own AES 256
symmetric key and provide it to google cloud storage for encryption/decryption operations. The CSEK is only stored in storage system memory and never persisted on any Google Cloud device

Cloud storage does not permanently store user’s key on Google’s servers or otherwise manage user’s key. Instead, the user provide key for each cloud storage operation, and the key is purged from Google’s server after completion of the operation. The customer-supplied encryption key is hashed and then purged from the storage system. The cryptographic hash is used to validate (future requests) but cannot be used to decrypt data or to reconstruct a key When the customer supplies the encryption key, cloud storage uses the key while encrypting

  • the object data
  • the object’s checksum
  • the object’s hash

Cloud Storage uses standard server-side keys to encrypt the remaining metadata for the object, including the object’s name.Encryption and Decryption workflow mentioned below:

  1. The CSEK is provided to Google Cloud Storage along with the data upload
  2. Data is broken into sub-file chunks
  3. A Google Cloud Storage system calls a common cryptographic library that Google maintains, called CrunchyCrypt, to generate a unique, one-time key called DEK
  4. Each data chunk is encrypted using a DEK
  5. The storage system then uses the CSEK as the KEK and encrypts the DEK
  6. The encrypted DEK is stored alongside the ciphertext chunk it encrypted in Google Cloud Storage while the plaintext version of the DEK is deleted from memory
  7. The customer-supplied encryption key is hashed and then purged from the storage system. The cryptographic hash is used to validate future requests but cannot be used to decrypt data or reconstruct the key
  8. The client or application requests data from Google Cloud Storage while supplying the CSEK
  9. Google Cloud Storage identifies the chunks in which the data is stored and where the chunks reside and retrieves the chunks
  10. For each data chunk, the storage system retrieves the encrypted DEK and decrypts it using the CSEK
  11. Once the decryption is done using DEK, the storage system discards the DEK and sends the decrypted data to the client or application that requested the data
Customer-managed encryption keys:

Customer-managed encryption keys are keys generated for users by Cloud Key Management Service (KMS), that the user manages themselves. These keys act as an additional encryption layer on top of the standard Cloud Storage encryption.The encryption and decryption workflow:

  1. Data is broken into sub-file chunks after being uploaded to Google Cloud
  2. A Google Cloud Storage system calls a common cryptographic library that Google maintains, called CrunchyCrypt, to generate a unique one-time use DEK
  3. Each data chunk is encrypted using a DEK
  4. The storage system then sends the DEK to Google’s Key Management Service (KMS) to be encrypted using that storage system’s associated Key Encryption Key (KEK)
  5. The encrypted DEK is stored alongside the ciphertext chunk it encrypted in Google Cloud Storage while the plaintext version of the DEK is deleted from memory
  6. When data is requested, Google Cloud Storage identifies the chunks in which the data is stored and where the chunks reside and retrieves the chunks
  7. For each data chunk, the storage system retrieves the encrypted DEK and sends it to Google’s KMS for decryption
  8. KMS sends the decrypted DEK to the storage system where it is used to decrypt the data
  9. The storage system discards the DEK and sends the decrypted data to the client that requested the data

Client-side encryption:

With this option, Users create and manages its own encryption keys. Users must encrypt the data before sending it to cloud storage. The encrypted data on the client side arrives at cloud storage in an encrypted state. When cloud storage receives the data, one more time the data will be encrypted. This second encryption is called server-side encryption, which Cloud Storage manages. While retrieving the data, cloud storage removes the server-side layer of encryption, but user must decrypt the client-side layer by themselves.

Benefits

Customer-managed keys provide the following benefits:

  • More Control over Data Access:
    • Customer-managed keys provide an extra level of security for customers with sensitive data.
    • When the customer decides to disable access, data can no longer be decrypted
  • Stop Data Breaches:
    • In this case, disabling customer-managed keys will allows customers to stop ongoing exfiltration of their data
  • More Control over Data Lifecycle:
    • Using customer-managed keys, sensitive data is encrypted with the customer’s key. Without customer’s/users consent no one can decrypt the data
    • The customer has full control over the data’s lifecycle
  • Secure
    • Compute assets are encrypted using the industry-leading AES-256 standard, and Google never retains users’ keys, meaning Google cannot decrypt user’s data at rest.
  • Comprehensive
    • Customer-Supplied Encryption Keys cover all forms of data at rest for Compute Engine, including boot and data persistent disks.
  • Fast
    • Google Compute Engine is already encrypting user’s data at rest, and Customer-Supplied Encryption Keys gives user greater control, without additional overhead.

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In this article, we will take a closer look at Google’s Cloud Key Management Services. When users store data into Google Cloud, the data is automatically encrypted at rest. We use Google’s Cloud Key Management service to gain better control over managing the encrypted data-at-rest and encryption keys.

Source and Control of cryptographic keys

Cloud KMS lets users manage cryptographic keys in a central cloud service for direct use or use with other resources and applications. The keys that have to be used must be from one of these sources:

  • Cloud KMS’s software backed key gives users the ability to encrypt data with either a symmetric or asymmetric key that the users control.
  • CloudHSM provides hardware keys. Symmetric and asymmetric keys are only used in FIPS 140-2 Level 3 validated Hardware Security Modules(HSMs).
  • Bring Your Own Key(BYOK) is also available for users to import their cryptographic keys into Cloud KMS.
  • Cloud External Key Manager (Cloud EKM), which uses external Key Managers such as Thales or Fortanix can also be used.


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Figure: Cloud EKM providing bridge between KMS and External Key Manager

Cryptographic keys in Cloud KMS

This section describes keys, key versions, and the grouping of keys into keyrings. The following diagram illustrates key groupings.


Key: A named object which represents a cryptographic key. It is a pointer to a key, and the actual bits or the key may change as we rotate the keys or create newer versions of the keys.

CloudKMS supports both asymmetric keys and symmetric keys. A symmetric key is used for symmetric encryption to protect some corpus of data, such as using AES-256 in GCM mode to encrypt a block of plaintext. An asymmetric key can be used for asymmetric encryption or for creating digital signatures.

Keyring: Keys are grouped into one keyring to organize the keys better. A keyring belongs to a specific Google Cloud project and resides in a particular location. Key inherit IAM policies from the keyrings that contains them.Grouping keys with related permissions in a keyring lets you grant, revoke, or modify permissions to those keys at the keyring level, without needing to act on each key individually. Keyrings provide convenience and categorization, but if the grouping of keyrings is not useful to you, you can manage permissions directly on keys.Key metadata: Resource names, properties of KMS resources such as IAM policies, key type, key size, key state, and any data derived from the above. Key metadata can be managed differently than the key material.

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CloudKMS components

In this section, we discuss a few points about additional parameters associated to Google CloudKMS resources such as keys and keyrings.

  • ProjectGoogle Cloud KMS resources belong to Google Cloud Project, like all other Google Cloud Resources. Users can host data in a project that is different from the project in which Cloud KMS keys reside. This capability supports the best practice of separation of duties between the key administrators and data administrators.
  • LocationsWithin a project, Cloud KMS resources are created in one location.

Key Hierarchy

The following diagram illustrates the key hierarchy of Google’s internal Key Management Service. Cloud KMS leverages Google’s internal KMS in that Cloud KMS-encrypted keys are wrapped by Google KMS. Cloud KMS uses the same root of trust as Google KMS.

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

CloudKMS platform overview

The Cloud KMS platform supports multiple cryptographic algorithms and provides methods to encrypt and digitally sign using both hardware and software-backed keys.


The diagram shows the main components of the Cloud KMS platform.Administrators access key management services by using the Google Cloud Console, the gcloud command-line tool, or through applications implementing the REST or gRPC APIs.Applications access key management services using a REST API or gRPC.

Applications can use Google services that are enabled to use customer-managed encryption keys (CMEK). CMEK, in turn, uses the Cloud KMS API. The Cloud KMS API lets users use either software (Cloud KMS) or hardware (Cloud HSM) keys. Both software and hardware-based keys leverage Google’s redundant backup protections.

With the Cloud KMS platform, users can choose a protection level when creating a key to determine which key backend creates the key and performs all future cryptographic operations on that key.

The Cloud KMS platform provides two backends (excluding Cloud EKM), which are exposed in the Cloud KMS API as

  • Software Protection Level The protection level software applies to keys that may be unwrapped by a software security module to perform cryptographic operations.
  • HSM protection Level The protection level HSM applies to keys that can only be unwrapped by Hardware Security Modules that perform all cryptographic operations with the keys.

Google Cloud supports CMEK for several services, including

  • Cloud Storage
  • BigQuery
  • Compute Engine.

CMEK lets users use the Cloud KMS platform to manage the encryption keys that these services use to help protect their data.Cloud KMS cryptographic operations are performed by FIPS 140-2 validated modules.

  • Keys with protection level software, and the cryptographic operations performed with them, comply with FIPS 140-2 Level 1.
  • Keys with protection level HSM, and the cryptographic operations performed with them, comply with FIPS 140-2 Level 3.

References

www.cloud.google.com/kms/docs

www.cloud.google.com/security-key-management

www.cloud.google.com/sdk/gcloud/reference/kms

www.googleapis.dev/python/cloudkms/latest/UPGRADING.html

About the Author

Anish Bhattacharya is a Consultant at Encryption Consulting, working with PKIs, HSMs, creating Google Cloud applications, and working as a consultant with high-profile clients.

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Application Programming Interface (API) is a software intermediatory which allows two separate applications to communicate with each other. These two applications might be totally different and are built using two different languages but can communicate in a defined format that both understand. Everything we play a video on YouTube or stream music, we are essentially using an API for this purpose.

When a client communicates with a server or a different application to retrieve information that can be shown to a user, the communication happens via an intermediatory, which is often an API. An API makes it possible to exchange information between an application and the server or for two separate applications to exchange information.

Does API provide more security?

API never exposes a server to the application or vice versa. API carries the request from the client, and the server processes that request and sends the information accordingly. API also carries some rules which make only the necessary information with a certain format viable. If the format is not fulfilled or all necessary information isn’t provided, then API may fail to carry back any relevant information, which can reduce data exposure or other such attacks.
Most companies provide paid API for other developers to use. API such as stripe can provide developers with the tools to quickly develop an app with a payment gateway by using stripe’s API. Google, eBay, and Amazon also expose such APIs, which can generate revenue for the company without being a security risk.

Features of an API

API provides some characteristics and features which make it more developer-friendly, secure, and accessible throughout the web. Some of them include:

  • APIs adhere to strict standards (such as HTTP, Rest, or GraphQL), which makes API developer-friendly, and easily understood by many.
  • API are treated as mini-applications or products and is targeted towards web or mobile developers. APIs are usually well documented and are versioned and updated. API developers also listen to the community and keep updating, maintaining the API throughout its lifecycle.
  • API do carry heavier security, governance over the access of the service. There are API keys associated which are required to access the API. APIs are also monitored and managed, as well as scaled according to the performance being monitored.

About the Author

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A collection of Encryption related products and resources that every organization should have!

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Datasheet of Encryption Consulting Services

Encryption Consulting is a customer focused cybersecurity firm that provides a multitude of services in all aspects of encryption for our clients.

Download

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