Log .

2023-03-08 · 6분

Terraform Basics

Terraform basics — a full AWS web service provisioning example: VPC, subnets, IGW/NAT, security groups, IAM, S3, RDS, ALB, ECR, ECS and CloudWatch, resource by resource.

cloudterraform

2023-03-06 · 2분

AWS SSM (Systems Manager) — Patch Manager

What Patch Manager does and which OS fleets it covers, then a hands-on: a custom Amazon Linux 2 patch baseline, a maintenance window, and a registered Run Command task that patches on schedule.

cloudawsssm

2023-03-06 · 3분

AWS SSM (Systems Manager) — Run Command

Using Systems Manager Run Command to manage EC2 without SSH or a bastion host: creating the IAM role, launching an instance, updating the SSM Agent, and running a shell script to install nginx.

cloudawsssm

2023-02-28 · 5분

AWS SSM (Systems Manager) — Session Manager

How Systems Manager works, then replacing SSH with Session Manager: an IAM role with AmazonSSMManagedInstanceCore on a private EC2, plus the 2023 Default Host Management Configuration (DHMC) that removes the need for instance profiles.

cloudawsssm

cloudawscloudwatchcloudtrail

2023-02-22 · 8분

AWS Cloud Service Logs (CloudWatch & CloudTrail)

The four kinds of AWS logs, monitoring metrics and billing alarms with CloudWatch, and auditing account activity with CloudTrail — concepts plus hands-on practice.

2023-02-22 · 7분

AWS Organizations & AWS IAM

How Organizations and IAM differ (accounts vs users, SCP precedence), IAM's feature set — shared access, granular permissions, MFA, federation, PCI DSS — plus the ways to access IAM and Organizations' OU/SCP/consolidated-billing features.

cloudawsiam

2023-02-17 · 4분

Vim

A quick Vim reference: what Vim is and why it beats plain shortcuts, NORMAL/INSERT modes, navigation and editing commands, plus the Command + Object grammar (d3w, dit, daw) for advanced use.

vimlinux

2023-01-12 · 5분

AWS EFS (Elastic File System)

EFS concepts — availability, scaling, storage classes, lifecycle, performance/throughput modes, backup options — then a hands-on: NFS security group, file system creation, and mounting it from two EC2 instances across AZs.

cloudaws

2023-01-11 · 8분

AWS EC2 (Elastic Compute Cloud)

What EC2 is and why it helps, then a full hands-on: launching an instance with key pairs, security groups and user-data, assigning an EIP, connecting over SSH, and cloning it with an AMI.

cloudawsec2

2023-01-11 · 5분

VPC, Subnet, Internet Gateway & Route Table

From VPN to VPC: what VPCs, subnets, internet gateways, and route tables are, then building them by hand — a 10.0.0.0/16 VPC, public/private subnets across two AZs, IGW attachment, and routing that keeps private subnets offline.

cloudvpc

2023-01-10 · 4분

AWS CloudFront (CDN)

What a CDN is, why it helps, and how CloudFront works — Origin and Edge servers, cache TTL and invalidation, plus a hands-on speed test against S3.

cloudaws

2023-01-10 · 4분

Amazon S3 (Simple Storage Service)

What S3 is, its characteristics and core terms (object, bucket, versioning, RRS, Glacier), then a hands-on: hosting a static website on a bucket, including fixing 403s with public-access settings and a getObject bucket policy.

cloudawss3

2023-01-04 · 2분

Pentest Practice — SQL Injection

A payload cheatsheet from SQLi practice: error-based, union-based, blind, and time-based injection, plus quick notes on sqlmap, hashcat, SSRF bypasses, and Log4j JNDI strings.

securityweb

2022

2022-11-15 · 9분

Network Study 2 — DNS, DHCP & DMVPN

A hands-on lab building a Debian DNS (bind9) and DHCP server, then wiring a hub-and-spoke network with mGRE/DMVPN and NHRP (disabling EIGRP split-horizon), and finally issuing an SSL certificate via a router CA over FTP.

2022-11-14 · 6분

Network Study 1 — GRE & IPSec

Study notes on network security: symmetric vs asymmetric crypto and certificates (Issuer, CDP/CRL), the GRE tunneling protocol and its header/MTU concerns, and a step-by-step IPSec VPN configuration flow (IKE phase 1/2, transform-set, crypto map).

2022-11-01 · 4분

Docker Basics

A working note on Docker essentials: installing it, pulling OS images, running containers with systemctl support and port forwarding, and managing custom networks with docker network create and inspect.

docker

2022-04-09 · 23분

[영어] 2021 11월 고2 영어 모의고사

학교 중간고사 공부를 위해 정리하므로, 21~24번, 29~34번만 올립니다.

englishstudy

2022-04-09 · 4분

Korean Poem — "Spring Snow" (Chunseol)

A literary study of Jeong Ji-yong's poem "Chunseol (Spring Snow)": the poem itself, a stanza-by-stanza analysis of its synesthetic imagery (visual→tactile/olfactory), exclamation, irony and paradox, and its theme of spring's vitality felt through unseasonal snow.

koreanstudy

2022-02-11 · 3분

Shell Script

A shell-script cheatsheet: basic form and variables, conditionals (if/elif/else/fi), a numeric/string/file comparison-operator table, case, loops (for/while), and worked examples — a host-name loop, seq loop, and an nginx start/restart/stop/status service script.

linuxshell

2022-02-09 · 3분

VLAN & Inter-VLAN

What VLANs and Inter-VLAN routing are, Access vs Trunk ports, a Packet Tracer lab configuring VLAN 10/20 with trunk uplinks and router sub-interfaces, and a packet analysis showing 802.1Q tagging.

2022-02-03 · 2분

Server Build 4

A VMware lab extending the previous topology — adding router2, Vmnet2, and a client-server (cloning existing VMs), redoing Vmnet/IP and netplan settings, static routing between zones, and DNS zones for sunrin.com / skills.com / cs.com.

2022-02-02 · 5분

MAC Address & RIP

A Packet Tracer lab on dynamic routing with RIP/RIPv2, then a PDU-level packet analysis tracing how the destination MAC address changes hop-by-hop through routers (including HDLC framing) between two PCs on different networks.

2022-01-28 · 5분

Server Build 3

The third server-build lab: Linux account management (groups, useradd options, chage password aging), restricting SSH to the semiAdmin group via sshd_config, and setting up a bind9 DNS server with forward/reverse zones for sunrin.com.

2022-01-27 · 5분

About NAT

What NAT is and why it exists (IPv4 exhaustion + private/public addressing), then Packet Tracer labs for static NAT, dynamic NAT with ACLs and an address pool, and PAT sharing one interface address by port.

2022-01-27 · 7분

Server Build 2

The second server-build lab: NAT masquerade so clients reach the servers but not vice-versa, enabling SSH and root login via sshd_config, serving web with Apache2 and nginx (and changing their document roots), and an iptables reference.

2022-01-25 · 4분

Server Build 1

The first server-build lab: composing virtual networks and VMs in VMware, configuring the network adapters and IPs of the main/slave servers and clients to match the topology, and getting pings to pass through the router.

2022-01-18 · 9분

Information Security — System Security (Part 2)

System-security study notes: malware taxonomy (viruses, trojans, worms, mail bombs, jokes, spyware), trojan capabilities and detection, real trojan/rootkit cases (NetBus, Back Orifice, rootkits), and public hacking tools — cracking and port scanning (NMap scan types).

securitycertificate

2022-01-13 · 2분

Dedicated Registers

Study notes on the CPU's dedicated registers — accumulator, program counter, instruction register, MAR, MBR, status, data, and address registers — and which are user-visible versus user-invisible.

2022-01-13 · 27분

Information Security — System Security (Part 1)

System-security study notes: CPU components and registers, the instruction execution cycle, interrupts, the memory hierarchy and management (paging/segmentation/virtual memory), I/O management and channels, an OS overview (kernel, dual mode, scheduling, deadlock), and secure-OS topics (access control, security kernel, TCB, TPM).

securitycertificate

2021

2021-12-21 · 18분

[영어] 2019 고1 11월 모의고사 해석

시험대비로 공부하기에 20, 21, 22, 29, 33, 37, 38, 41번만 진행합니다.

englishstudy

2021-12-15 · 17분

[영어] 2021 고1 9월 모의고사 해석

시험대비로 공부하기에 35번부터 41번까지 진행합니다.

englishstudy

2021-11-07 · 1분

What's the Stack Frame?

What a stack frame is — the per-function stack region holding parameters, return address, and local variables — and how the function prologue (push rbp; mov rbp, rsp) and epilogue (pop rbp; ret) set it up and tear it down.

2021-09-09 · 2분

Buffer Overflow (BOF)

An intro to the buffer overflow vulnerability: what it is, how HackCTF #1's fgets(s, 45, ...) into a size-40 buffer overwrites past s[40] to control v5, and how an unbounded scanf("%s") lets you overwrite the SFP and return address.

2021-09-09 · 2분

FSB (Format String Bug)

An intro to the Format String Bug: how a missing argument to printf lets you leak the stack with %p and %[n]$p, corrupt memory with %n, a table of printf format characters, and using pwntools' fmtstr_payload for exploitation.

2021-09-09 · 2분

GrabCON CTF — Can You write-up

A GrabCON pwnable write-up (cancancan): after chasing a stack-canary leak red herring, realizing printf(buf) has an FSB at offset 6 and overwriting read's GOT entry with the win function.

2021-09-09 · 1분

GrabCON CTF — Easy Bin write-up

A GrabCON pwnable write-up: a trivial 64-bit BOF where the payload is dummy[48] + sfp[8] + vuln, solved out of 4 challenges (3 solved).

2021-09-09 · 1분

GrabCON CTF — Pwn write-up

The last GrabCON pwnable: main is hidden so you trace from start to find sub_1357, and since NX is disabled (despite PIE) you exploit the vulnerability in sub_103D with shellcode.

2021-09-09 · 1분

HackCTF Basic_BOF #1 write-up

A HackCTF Basic_BOF write-up: a size-40 buffer s read with fgets up to 45 bytes overflows into v5, so the payload dummy[40] + 0xDEADBEEF sets v5 and triggers system("/bin/dash").

2021-09-09 · 1분

HackCTF Basic_BOF #2 write-up

A HackCTF Basic_BOF write-up: overflow via fgets to fill dummy[128] and overwrite the v5 function pointer with the shell function's address, so the v5() call runs shell — reading the code beats blindly applying known techniques.

2021-09-09 · 1분

HackCTF Basic_FSB write-up

A HackCTF Basic_FSB write-up: the vuln function's snprintf(format, 0x400, s) has a format string bug at offset 2, which is used to overwrite printf's GOT with the flag function.

2021-07-14 · 4분

rev-basic 0~3 write-up

Write-ups for Dreamhack rev-basic 0 through 3: analyzing the compare routine with radare2/IDA to recover string, character, and array flags, and reversing an XOR+arithmetic transform in Python for the final one.

2021-07-14 · 4분

rev-basic 4~6 write-up

Write-ups for Dreamhack rev-basic 4 through 6: a nibble-swap transform reversed in Python, a running-sum transform reversed from the back, and a simple key-lookup mapping for the final flag.

2021-07-10 · 4분

CPU Registers

A reversing reference on x86 registers: general-purpose registers (EAX/EDX/ECX/EBX/ESI/EDI), the stack/base/instruction pointers, endianness, operand types and common instructions, the flags register, and the call / leave-ret function epilogue.

2021-07-10 · 1분

Getting Started with Hacking

An intro to hacking: what it is (and how it differs from cracking), the types (technical vs social engineering), the categories (war, money & honor, career, hobby), the relationship between development and hacking, and how to study for CTFs.

security

2021-07-10 · 1분

Getting Started with Reversing

An intro to reverse engineering for CTFs: the three steps (analyze structure, reimplement, get the flag via inverse operations), the base knowledge needed (Linux, programming, C), and how source compiles through .i/.s/.o stages to a binary.

2021-06-27 · 3분

What is CSS?

A beginner's intro to CSS: what it is, the three ways to apply it to HTML (inline/internal/external) and their priority, the main selector types, id vs class, and fun pseudo-selector examples like ::selection and :hover.

cssweb

2021-06-20 · 1분

BOJ 11047 — Coin 0

A short write-up for BOJ 11047 (Coin 0), a greedy coin problem.

2021-06-16 · 2분

BOJ 7569 — Tomato

A short write-up for BOJ 7569 (Tomato), a 3D BFS problem.

2021-06-06 · 4분

LOS #1 gremlin write-up

A write-up for the first level of Lord of SQL Injection (gremlin): understanding the PHP preg_match filter and GET query, then a basic ' or 1=1 %23 injection to make the id condition true, with notes on URL encoding and why # comments in MySQL.

2021-06-06 · 1분

LOS #2 cobolt write-up

A write-up for the second Lord of SQL Injection level (cobolt): the query now checks $result['id'] == 'admin', so instead of plain ' or 1=1, inject id=admin' %23 to force the id to admin and comment out the rest.

2021-06-06 · 1분

LOS #3 goblin write-up

A write-up for the third Lord of SQL Injection level (goblin): id is fixed to guest and only no= is user-controlled, and special characters are filtered — so use ASCII codes (CHAR) to inject and turn the id into admin.

2021-06-06 · 6분

Regular Expressions Cheatsheet

A regex reference: what a regular expression is, the meta characters (^x, x$, x+, x?, x*, groups, quantifiers), character-class/escape sequences ([xy], \b, \d, \s, \w), and the g/i/m flags.

regextil

2021-06-04 · 2분

C Pointers

A beginner's explanation of pointers in C/C++: what a pointer is (a variable holding a memory address), how to declare and initialize one with &, and the crucial distinction between *p (the value at the address) and p (the address itself).

ctil

2021-06-03 · 2분

BOJ 1158 — Josephus Problem

Solving BOJ 1158 with a queue: the Josephus problem defined, and the approach of push-then-pop N-1 times and front-then-pop on the Nth to produce the elimination order.

2021-06-03 · 1분

BOJ 9012 — Parentheses

Solving BOJ 9012 with a stack: what a Valid PS (VPS) is, and the approach of pushing on '(', popping on ')' (FALSE if empty), and returning FALSE if the stack isn't empty at the end.

2021-06-03 · 2분

Data Structure — Queue

What a queue is (a FIFO structure, the opposite of a stack), its operations (push/pop/front/back/size/empty/swap), typical use cases like BFS and process management, and how to use C++'s STL queue — with BOJ 10845 as the practice problem.

algorithm

2021-06-03 · 3분

Data Structure — Stack

What a stack is (a LIFO structure), its core operations (push/pop/top/size/empty), why use it over an array, and how to use C++'s STL stack — with BOJ 10828 as the practice problem.

algorithm

2021-06-03 · 4분

SQL Injection

An overview of SQL Injection: what it is, and the major attack types — logical-error (' or 1=1--), Union-based, Blind, Time-based, Stored Procedure, and Error-based — plus a reference table of characters commonly used in injections.

securityweb