Digital Certificate
A digital certificate is an electronic credential used within z/OS to verify the identity of users, applications, or systems, and to enable secure, encrypted communication. It binds a public key to an entity's identity, issued and digitally signed by a trusted Certificate Authority (CA). In the mainframe context, they are crucial for establishing trust and confidentiality for network services and data. A Digital Certificate is an electronic credential used in z/OS and mainframe environments to cryptographically bind a public key to an identity, such as a user, server, or application. Its primary purpose is to verify identity, ensure data integrity, and enable secure communication channels, typically through protocols like TLS/SSL.
Key Characteristics
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- X.509 Standard: Digital certificates on z/OS adhere to the globally recognized X.509 standard, defining their format and content.
- Identity Binding: Each certificate contains an entity's public key, identity information (e.g., hostname, user ID, organization), and the digital signature of the issuing CA.
- Trust Chain: Certificates form a chain of trust, linking back to a root CA certificate, which must be trusted by the z/OS system or application.
- Managed by ESMs: On z/OS, digital certificates and their associated private keys are primarily managed by External Security Managers (ESMs) like RACF, ACF2, or Top Secret, often stored in key rings.
- Validity Period: Certificates have a defined start and end date, after which they expire and must be renewed or replaced.
- Public/Private Key Pair: A digital certificate contains the public key, which is part of a cryptographic key pair where the corresponding private key is securely stored and managed on the z/OS system.
Use Cases
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- Secure TCP/IP Communication (SSL/TLS): Enabling secure connections for services like z/OSMF, CICS Web Services, DB2 Distributed Data Facility (DDF), FTP, TN3270E, and HTTP servers (e.g., IBM HTTP Server for z/OS).
- Client/Server Authentication: Verifying the identity of clients connecting to z/OS applications or z/OS systems authenticating to external services.
- Digital Signatures: Providing non-repudiation and integrity for data, ensuring that data has not been tampered with and originated from a verified source.
- Code Signing: Verifying the authenticity and integrity of executable code or modules deployed on z/OS.
- VPN and Secure Shell (SSH): Used by z/OS components like OpenSSH for z/OS for secure remote access and data tunneling.
Related Concepts
Digital certificates are foundational to Public Key Infrastructure (PKI), with z/OS providing its own PKI Services. They are intrinsically linked to RACF (Resource Access Control Facility), which provides the RACDCERT command set for managing certificates and key rings where certificates and private keys are stored. Certificates are essential for System SSL (part of z/OS Communications Server) to establish secure SSL/TLS sessions, enabling encrypted communication for various z/OS applications and services.
- Secure Private Keys: Ensure that private keys associated with certificates are stored securely within the ESM (e.g., RACF) and protected from unauthorized access, potentially using hardware security modules (HSMs).
- Manage Certificate Lifecycle: Implement robust processes for issuing, renewing, and revoking certificates, ensuring timely renewal before expiration and immediate revocation of compromised certificates.
- Use Trusted Certificate Authorities: Only use certificates issued by reputable and trusted CAs, or maintain a well-managed internal CA for enterprise-specific needs.
- Regular Auditing: Periodically review certificate usage, key ring definitions, and security configurations (e.g.,
RACDCERTsettings) to ensure compliance and identify potential vulnerabilities. - Strong Cryptographic Algorithms: Configure z/OS applications and System SSL to use strong cryptographic algorithms and key lengths for certificate generation and secure communication.