calofmijuck/blog
1
0
Fork 0
mirror of https://github.com/calofmijuck/blog.git synced 2025-12-06 22:53:51 +00:00
Code Issues Packages Projects Releases Wiki Activity

feat: fixing equations and new post (#99)

Browse Source 
* [PUBLISHER] upload files #93

* [PUBLISHER] upload files #94

* PUSH NOTE : 03. Symmetric Key Cryptography (2).md

* PUSH ATTACHMENT : is-03-ecb-encryption.png

* PUSH ATTACHMENT : is-03-cbc-encryption.png

* PUSH ATTACHMENT : is-03-cfb-encryption.png

* PUSH ATTACHMENT : is-03-ofb-encryption.png

* PUSH ATTACHMENT : is-03-ctr-encryption.png

* [PUBLISHER] upload files #95

* PUSH NOTE : 03. Symmetric Key Cryptography (2).md

* PUSH ATTACHMENT : is-03-feistel-function.png

* PUSH ATTACHMENT : is-03-ecb-encryption.png

* PUSH ATTACHMENT : is-03-cbc-encryption.png

* PUSH ATTACHMENT : is-03-cfb-encryption.png

* PUSH ATTACHMENT : is-03-ofb-encryption.png

* PUSH ATTACHMENT : is-03-ctr-encryption.png

* [PUBLISHER] upload files #96

* PUSH NOTE : 03. Symmetric Key Cryptography (2).md

* PUSH ATTACHMENT : is-03-feistel-function.png

* PUSH ATTACHMENT : is-03-ecb-encryption.png

* PUSH ATTACHMENT : is-03-cbc-encryption.png

* PUSH ATTACHMENT : is-03-cfb-encryption.png

* PUSH ATTACHMENT : is-03-ofb-encryption.png

* PUSH ATTACHMENT : is-03-ctr-encryption.png

* [PUBLISHER] upload files #97

* [PUBLISHER] upload files #98

* style: tab to space
This commit is contained in:
Sungchan Yi
2023-10-06 21:59:54 +09:00
committed by GitHub
parent d0d95a00f8
commit 71d37da2a5
9 changed files with 274 additions and 24 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
_posts/Lecture Notes/Internet Security/2023-09-11-symmetric-key-cryptography-1.md
View File

@@ -7,8 +7,8 @@ categories:
- Internet Security
tags:
- security
- network
- lecture-note
- cryptography
title: 02. Symmetric Key Cryptography (1)
date: 2023-09-11
github_title: 2023-09-11-symmetric-key-cryptography-1
@@ -94,7 +94,7 @@ To attack this scheme, find the key length by *index of coincidence*. Then use f
#### Hill Cipher
- A polyalphabetic substitution
- A key is a *invertible* matrix $K = (k_{ij})_{m \times m}$ where $k_{ij} \in \mathbb{Z}_{26}$.
- A key is a *invertible* matrix $K = (k _ {ij}) _ {m \times m}$ where $k _ {ij} \in \mathbb{Z} _ {26}$.
- Encryption/decryption is done by multiplying $K$ or $K^{-1}$.
This scheme is vulnerable to known plaintext attack, since the equation can be solved for $K$.
@@ -218,7 +218,7 @@ To alleviate this problem, we can combine multiple LFSRs with a $k$-input binary
#### Encryption Overall
- Plaintext: Message +CRC
- Plaintext: Message + CRC
- CRC is padded to verify the integrity of the message.
- CRC is $32$ bits
- Not for attacks, but for error correction
@@ -256,13 +256,17 @@ To alleviate this problem, we can combine multiple LFSRs with a $k$-input binary
#### IV Collision
- The key is fixed, and the period of IV is $2^{24}$
- Same IV leads to same keystream.
- Same IV leads to same key stream.
- So if the adversary takes two frames with same IV to obtain the XOR of two plaintext messages.
- $c_1 \oplus c_2 = (p_1 \oplus k_s) \oplus (p_2 \oplus k_s) = p_1 \oplus p_2$
- Since network traffic contents are predictable, messages can be recovered.
- We are in the link layer, so HTTP, IP, TCP headers will be contained in the encrypted payload.
- The header formats are usually known.
#### CRC Algorithm
Given a bit string (defined in the specification), the sender performs long division on the data. The remainder is the result of the CRC, which is appended to the data. The receiver will check by performing long division, and the remainder should be $0$ if there were no bit errors during transmission.
### Message Modification
- CRC is actually a linear function.