Key Distribution

About

Key distribution is the process of securely sharing cryptographic keys between parties to ensure secure communication and data integrity. Effective key distribution is crucial for maintaining the security of cryptographic systems, including symmetric and asymmetric encryption.

Key Concepts

1. Key Distribution Methods

• Symmetric Key Distribution: Involves the sharing of a single secret key between parties. Both parties use the same key for encryption and decryption. The challenge lies in securely distributing the secret key without exposing it to potential attackers.

• Asymmetric Key Distribution: Uses a pair of keys (public and private). The public key can be freely distributed, while the private key is kept secret. This method simplifies key distribution as the public key can be shared openly without compromising security.

2. Key Management Systems (KMS)

Key Management Systems are tools and services designed to create, distribute, store, and manage cryptographic keys securely. KMS solutions provide automated and centralized management of keys, ensuring they are securely handled throughout their lifecycle.

3. Public Key Infrastructure (PKI)

PKI is a framework that uses asymmetric cryptography for securing communications and transactions. It involves key pairs and digital certificates issued by trusted Certificate Authorities (CAs). PKI facilitates secure key distribution and management by leveraging hierarchical trust models.

Use Cases

1. Secure Web Communications (SSL/TLS)

Scenario: A company needs to secure its web applications to protect user data transmitted over the internet.

Asymmetric Key Distribution:

• Certificate Authorities (CAs): Companies obtain SSL/TLS certificates from trusted CAs. The CA verifies the company's identity and issues a certificate containing the public key. The private key remains securely stored on the company's server.

• Key Exchange: During the SSL/TLS handshake, the server presents its certificate to the client. The client uses the public key to establish a secure session key (symmetric key) for encrypting the communication.

Symmetric Key Distribution:

• Session Keys: After the initial handshake, symmetric keys (session keys) are used for the duration of the session to encrypt data. These session keys are ephemeral and are destroyed after the session ends, enhancing security.

2. API Security in RESTful Services

Scenario: A company provides a set of RESTful APIs for external partners and clients, requiring secure access and data protection.

Asymmetric Key Distribution:

• OAuth 2.0 and JWT: Companies use OAuth 2.0 for secure authorization. JWTs are often used to convey authorization information. JWTs are signed with the company's private key and verified by clients using the corresponding public key.

• API Gateway: An API gateway manages key distribution by handling SSL/TLS termination and token validation. The gateway securely stores the private keys used for signing JWTs.

Symmetric Key Distribution:

• Shared Secrets: For certain internal APIs, companies might use shared secrets (symmetric keys) stored in secure environments. These secrets are used to encrypt and decrypt API payloads.

• Secrets Management: Tools like HashiCorp Vault or AWS Secrets Manager are used to store and manage these symmetric keys securely. Keys are rotated regularly to minimize risk.

3. Secure File Transfer

Scenario: A company needs to transfer sensitive files between internal systems and external partners securely.

Asymmetric Key Distribution:

• PGP/GPG: Companies use PGP or GPG for encrypting files before transfer. Each party generates a key pair, and public keys are exchanged securely. Files are encrypted with the recipient's public key and decrypted with their private key.

• SSH Keys for SFTP: SSH keys (asymmetric) are used for authenticating and establishing secure SFTP connections. The server holds the public key, and the client uses the private key to authenticate.

Symmetric Key Distribution:

• Ephemeral Keys: For bulk file encryption, symmetric keys are used after an initial asymmetric key exchange. The symmetric keys are generated for each session and are not reused, ensuring each transfer is uniquely encrypted.

4. IoT Device Authentication

Scenario: A company deploys IoT devices that need to communicate securely with central servers.

Asymmetric Key Distribution:

• Device Certificates: Each IoT device is provisioned with a unique certificate and key pair. These certificates are issued by the company's internal CA or a trusted external CA. During initial setup, devices authenticate with the server using their private key.

• Mutual Authentication: Both the server and IoT devices authenticate each other using their respective certificates, ensuring mutual trust.

Symmetric Key Distribution:

• Session Keys: Once authenticated, IoT devices and servers establish symmetric session keys for ongoing communication. These keys are generated dynamically and used for encrypting data streams.

• Key Management Services: Tools like AWS IoT Core or Azure IoT Hub manage the distribution and rotation of symmetric keys, ensuring secure and efficient key management.

5. Cloud Application Security

Scenario: A company leverages cloud services for its applications and needs to secure data both in transit and at rest.

Asymmetric Key Distribution:

• Cloud KMS Integration: Cloud providers offer Key Management Services (e.g., AWS KMS, Google Cloud KMS) that manage asymmetric keys. Companies integrate these services to handle key generation, distribution, and storage securely.

• Envelope Encryption: Data is encrypted using a data encryption key (DEK), which is then encrypted with a master key managed by the KMS. This approach combines symmetric and asymmetric encryption for enhanced security.

Symmetric Key Distribution:

• Data Encryption Keys (DEKs): Symmetric DEKs are used for encrypting bulk data. These keys are generated and rotated by the KMS. Encrypted DEKs are stored with the data, and the KMS decrypts them as needed.

• Automated Key Rotation: Cloud KMS solutions provide automated key rotation policies, ensuring symmetric keys are regularly updated without manual intervention.

Example

sFTP Transfer

A company ABC drops a file at a sFTP location in Linux system of company PQR. Company PQR then process that file and reshares it to company ABC at their sFTP location. Both uses asymmteric key encryption decryption of the data files.

Company ABC and PQR generates the private-public key on the linux system with the help of ssh-keygen and then shares the public key over the email with each other. Then they use repective public keys to encrypt data before sharing with others. Respective companies uses their private keys to decrypt the data before file processing