Operating System Core Functions and Digital Signature Essentials

Operating System Core Functions

A program in execution requires resources for its tasks. The Operating System (OS) is responsible for managing these resources through various core functions.

Process Management

The OS is responsible for:

• Creating and destroying processes.
• Pausing and resuming processes.
• Providing mechanisms to communicate and synchronize processes.

Memory Management

Memory is a table of words, each referenced using a unique address. The OS is accountable for:

• Knowing which parts of memory are used and by whom.
• Deciding which processes are loaded into memory when space is available.
• Assigning and reclaiming memory space when needed.

Secondary Storage Management

Secondary storage is necessary because main memory is volatile and often too small to store all programs and data. The OS is responsible for:

• Disk scheduling and planning.
• Managing free space.
• Assigning storage.

File System Management

Files are collections of related information defined by their creators. The OS is responsible for:

• Creating and deleting files and directories.
• Providing functions to manipulate files and directories.
• Establishing the correspondence between files and physical storage.
• Backing up files.

Protective Systems

Protective systems are mechanisms that control access to system resources. The OS is responsible for:

• Distinguishing between authorized and unauthorized use.
• Specifying the security controls to be performed.
• Enforcing the use of protection mechanisms.

Understanding Digital Signatures

What is a Digital Signature?

A digital signature refers to a cryptographic method that associates the identity of a person with a message or a document. It can be used to identify the author, to signify conformity (e.g., if you have read it), or to ensure that the content cannot be modified.

How Digital Signatures Work

The digital signature of a document is the result of applying a mathematical algorithm (often called a hash function) to its content, and subsequently applying a signature algorithm using the signer's private key. The software must also perform various validations, including:

• Validity of the signer's digital certificate.
• Revocation status of the signer's digital certificate.
• Inclusion of a timestamp.

Types of Digital Signatures

• Basic Signature: Includes the result of the hash operation and the private key encryption.
• Dated Signature: Adds a timestamp from a Trusted Timestamping Authority (TSA) after calculating the document's hash. This proves the document existed in its signed form at a specific time.
• Full Signature: Adds comprehensive information regarding the certificate's validity, often obtained from a Certificate Revocation List (CRL) query, ensuring long-term validity and non-repudiation.