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Challenges are the core problems that participants solve in CTF competitions. GZCTF supports multiple challenge types to accommodate different scenarios and requirements.

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Challenge Types

GZCTF provides four distinct challenge types, each designed for specific use cases:

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Static Attachment

Static attachment challenges use shared files and flags across all teams.
Use case: Traditional challenges where all teams work with the same files and submit the same flag.
Characteristics:
  • Single attachment file shared by all teams
  • Any configured flag can be accepted
  • No team-specific differentiation
  • Ideal for reverse engineering, cryptography, and forensics challenges

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Dynamic Attachment

Dynamic attachment challenges distribute unique attachments and flags to each team.
The number of flags and attachments must be at least equal to the number of participating teams.
Characteristics:
  • Each team receives a unique attachment
  • Flags are distributed according to teams
  • Prevents flag sharing between teams
  • Suitable for challenges requiring flag uniqueness

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Static Container

Static container challenges use shared Docker containers without dynamic flag generation. Characteristics:
  • All teams use the same container template
  • No dynamic flags issued
  • Any configured flag can be submitted
  • Container resource limits apply
Container Configuration:
  • Memory Limit: Default 64 MB
  • Storage Limit: Default 256 MB
  • CPU Count: Default 0.1 CPUs (1 = 1 CPU core)
  • Exposed Port: Default port 80

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Dynamic Container

Dynamic container challenges automatically generate unique flags for each team via container environment variables.
Flags are generated using the flag template and passed to containers as environment variables at runtime.
Characteristics:
  • Each team receives a unique container instance
  • Flags are automatically generated and unique per team
  • Prevents flag sharing
  • Supports traffic capture for monitoring
Network Modes:
  • Open: Container can access external networks including the internet
  • Isolated: Container cannot access external networks (internal only)
  • Custom: Uses user-defined network configuration (Docker network or K8s label)

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Challenge Categories

GZCTF supports the following challenge categories:

Misc

Crypto

Pwn

Web

Reverse

Blockchain

Forensics

Hardware

Mobile

PPC

AI

Pentest

OSINT

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Challenge Properties

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Basic Information

PropertyDescription
TitleChallenge name (required)
ContentChallenge description and instructions (required)
CategoryChallenge category (default: Misc)
TypeChallenge type - cannot be changed after creation
IsEnabledWhether the challenge is currently active
HintsOptional list of hints for participants

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Constraints

Deadline Challenges can have an optional deadline. After the deadline, submissions are no longer accepted. 
DateTimeOffset? DeadlineUtc
Submission Limit Limit the number of flag submissions per team. Set to 0 for unlimited submissions. 
int SubmissionLimit // 0 = no limit

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Container Challenges

For container-based challenges, additional properties are available:
PropertyDefaultDescription
ContainerImage-Docker image name and tag
MemoryLimit64 MBMemory allocation
StorageLimit256 MBDisk storage
CPUCount1 (0.1 CPU)CPU allocation in 0.1 CPU units
ExposePort80Container port to expose
NetworkModeOpenNetwork isolation level

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Flag Templates

Dynamic challenges use flag templates to generate unique flags for each team. 
flag{[TEAM_HASH]_welcome_to_gzctf}
The [TEAM_HASH] placeholder is replaced with a team-specific hash generated from:
  • Game’s team hash salt
  • Challenge ID
  • Team participation token
Flag templates support leet speak transformations and custom placeholders for advanced use cases.

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Challenge Model Reference

The Challenge model is located at: 
~/workspace/source/src/GZCTF/Models/Data/Challenge.cs

public class Challenge
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    public ChallengeCategory Category { get; set; }
    public ChallengeType Type { get; set; }
    public List<string>? Hints { get; set; }
    public bool IsEnabled { get; set; }
    public DateTimeOffset? DeadlineUtc { get; set; }
    public int SubmissionLimit { get; set; }
    
    // Container properties
    public string? ContainerImage { get; set; }
    public int? MemoryLimit { get; set; }  // MB
    public int? StorageLimit { get; set; } // MB
    public int? CPUCount { get; set; }     // 0.1 CPUs
    public int? ExposePort { get; set; }
    public NetworkMode? NetworkMode { get; set; }
    
    // Flag configuration
    public string? FlagTemplate { get; set; }
    public string? FileName { get; set; }
    
    // Relationships
    public Attachment? Attachment { get; set; }
    public Container? TestContainer { get; set; }
    public List<FlagContext> Flags { get; set; }
}

Dynamic Scoring

Learn how challenge scores decrease as more teams solve them

Container Management

Understand container lifecycle and management

Games

Explore how challenges are organized in games

Teams

See how teams participate in challenges

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