Encryption is an evasion technique that is a function of ransomware, which is a type of malware that encrypts the victim's files or system and demands a ransom for the decryption key. Encryption is used by ransomware to prevent the victim from accessing their data and to avoid detection by antivirus or other security tools.
Encryption can also be used by other types of malware to hide their communication, configuration, or payload from analysis. References:
* Understanding Cisco Cybersecurity Operations Fundamentals (CBROPS) v1.0, Module 3: Network Intrusion Analysis, Lesson 3.4: Malware
* Cisco Certified CyberOps Associate Overview, Exam Topics, 3.4 Compare and contrast types of malware

The Cuckoo report indicates that the file has been identified by Yara rules as being capable of detecting a sandbox environment, which is a security mechanism for isolating and analyzing suspicious code. The presence of the "vmdetect" and "anti_dog" Yara rules suggests that the file may have mechanisms to avoid executing its malicious behavior when it detects that it is being analyzed in a sandbox. This is a common evasion technique used by malware to prevent detection and analysis by security researchers or automated systems.

The unauthorized usage of "Tcpdump" tool indicates that the malicious insider was attempting to obtain all information within datagrams passing through a specific interface on the network. Tcpdump allows users to capture packet data from a live network or read packets from a previously saved capture file. References :
= Cisco CyberOps - Module 3: Network Data and Event Analysis

Corroborative evidence is the type of evidence that supports a theory or an assumption that results from initial evidence. It provides additional support to the initial findings, strengthening the theory or assumption by confirming the same facts or pointing towards the same conclusion with independent pieces of evidence4567.
References := Types of evidence (article) | Lessons | Khan Academy, Evidence: Fundamental Concepts and the Phenomenal Conception, Navigating Scientific Evidence: Types and Definitions, How Courts Work - American Bar Association