What really protects your computer or smartphone when someone gains physical access to it? Is a login password enough? Digital Forensics — Part One: Password Security, Credential Protection and Boot-Level Compromise Across Modern Operating Systems goes beyond the familiar login screen to examine what actually protects the credentials, encryption keys and sensitive data inside modern computing devices. Covering Windows, Linux, Android and iOS, the book explores how operating systems store, verify and protect passwords, PINs and cryptographic material—and what happens when those protections are challenged by physical access, boot-level attacks or forensic examination. Designed for cybersecurity professionals, digital-forensics investigators, system administrators, lecturers and students, the book combines academically grounded concepts with practical laboratory exercises covering Windows SAM and TPM security, BitLocker, Ubuntu /etc/shadow and LUKS, Android hardware-backed authentication, iOS Secure Enclave and Data Protection, volatile memory, boot-level security, cryptanalysis principles and forensic evidence preservation. Readers also work with professional forensic tools and techniques, including CAINE, PALADIN, dislocker, cryptsetup and PowerShell, transforming theoretical knowledge into practical skills that can be applied in authorized forensic and cybersecurity laboratories. Published by KKKT Digital as Part One of the Computer Forensics Series, the book brings together the expertise of Geofrey A. Kilimba, cybersecurity researcher; Jacob Mtui, systems and infrastructure-security specialist; and Dr. Kosmas Kapis, applied-cryptography specialist. At TZS 35,000, the package includes three selected digital-forensics tools for buyers, making this more than an eBook. It is a practical learning resource for understanding how operating-system security can fail, how modern security technologies resist compromise, and how forensic investigators can examine digital evidence responsibly.