The Missing Semester of Your CS Education¶

Info

Lecturer: Anish, Jon and Jose.

Course Website:

The Missing Semester of Your CS Education. (Chinese Version) [MIT 2020 version].

My Feedback and Things Needed to Know before learning this course

Generally, it's a course to teach you many useful tools, mostly based on command line. The environment is Mac OS / Linux based OS, and the shell they use is zsh. These tools help you doing things more efficiently and proficiently. However, I think having got a master of python and JSON will make you a better understanding of this course, which I haven't yet. :-<

Records on Youtube are really recomended, which also enables your learning skills through English. Because much content is not in the lecture notes.

By the way, Jose had quite an accent so English substitutions are recomended. :-)

1. Course Overview and the Shell¶

2. Shell Tools and Scripting¶

Script¶

Reference : Advanced Bash-Scripting Guide

Assignment foo=bar.
Access value $foo, $(foo), ${foo}.

Tip

Sometimes ${foo} is not allowed depending on shell. Thus $(foo) is usually used.

Space are the delimiters in shell. So foo = bar will be split to three arguments.

Difference between quote ' and "

Provided that foo=bar, then echo "$foo" prints bar and echo '$foo' prints $foo.

Return value
- Commands will ofter return output through STDOUT, errors through STDERR.
Special identifiers (selected, not all)
- $0 - Script name (command name).
- $1 to $9 - Arugments to the script.
- $@ - All the arguments.
- $# - Number of arguments.
- $? - Return code of the previous command. If the previous command executes successfully, $? will return 1, otherwise 0.
- $$ - Process identification number (PID) for the script
- !! - Entire last command. It's useful for sudo !!.
- $_ - Last argument from the last command.
Short-circuiting operators 短路运算符
- && and ||. The same meaning as in C language.
Substitution
- Command Substitution
  - $(CMD) will executes command CMD and its return value replaces $(CMD).
  - e.g. for file in $(ls) to iterate the files.
- Process Substitution
  - <(CMD) will executes command CMD and its return value will be stored in a temporary file. That's useful when the return value is passed by file instead of STDIN.
  - e.g. diff <(ls foo) <(ls bar).
Globbing 通配
- ? match one amount of characters, * match any amount of characters.
  - e.g. rm foo* will remove foo, foo1 and foo123. rm foo? will only remove foo1.
- {} expand the value in it.
  - e.g. touch {foo,bar}/{a..c} will expand to touch foo/a foo/b foo/c bar/a bar/b bar/c; convert image.{png,jpg} will exapand to convert image.png image.jpg.

Shebang

When writing bash script, you will commonly see #!/usr/bin... called shebang at the first line. When executed, it will run the script by the program this line specifies, not necessarily bash.

Use command env for shebang is a good pratice. e.g. #!/usr/bin/env python will let shell execute the script using python.

Example

The following script will iterate through the arguments of files and append # foobar if the file has no foobar.

#!/bin/bash

echo "Starting program at $(date)" # Date will be substituted

echo "Running program $0 with $# arguments with pid $$"

for file in "$@"; do
    grep foobar "$file" > /dev/null 2> /dev/null
    # When pattern is not found, grep has exit status 1
    # We redirect STDOUT and STDERR to a null register since we do not care about them
    if [[ $? -ne 0 ]]; then
        echo "File $file does not have any foobar, adding one"
        echo "# foobar" >> "$file"
    fi
done

Shell Tools¶

How to use commands?

man, CMD -h or CMD --help.
tldr (short for Too Long Don't Read) is also a good tool to search for frequently used methods of the command.

Finding Files¶

find

Simple usage
- find . -name src -type -d finds all the directories named srcin the current directory.
- find . -path '*/test/*.py' -type f finds all .py files that have a parent folder named testin the current directory.
- find . -mtime -1 finds all files modified in the last day.
- find . size +500k -size -10M -name '.tar.gz' finds all .tar.gz files with size ranging 500k to 10M.
Advanced usage
find . -name '*.tmp' -exec rm {} \; removes all .tmp files
find . -name '*.png' -exec convert {} {}.jpg \; convert all PNG files to JPG files.
Generally, PATTERN is used for match like find . -name 'PATTERN'. -iname is optional to ignore the letter case.

fd, a better tool than find.

locate

locate uses a database updated by updatedb.
It's faster to find files in some certain directories.

Finding Code¶

grep

-C for getting context around the matching result.
-v for inverting the result.
-R for recursive finding.

rg (short for ripgrep)

Example

rg -t py 'import requests' finds all .py files using requestslib.
rg -u --files-without-match "^#!" finds all files (including hidden files) without a shebang line.
rg foo -A 5 finds all match of fooand prints the following 5 lines.
rg -stats PATTERN print statistics of matches.

Find Shell Commands¶

history with grep.
Ctrl + R performs backwards search through history. It can be used with fzf.

history-based autosuggestions

It's first introduced by fish shell. This feature dynamically autocompletes the current shell command with the most recent command.

alias for command short cut. ln -s creates symbolic links.
fasd or autojump finds frequent or recent files and directories.
tree or brootgive an overview of a directory structure.
nnn or ranger is full fledged file manager.

3. Editors (Vim)¶

Since I've learned about vim before. For the detail of basic operations please see the lecture notes and other resources. The following are some supplements.

Vim-mode in other programs¶

Shell.
Readline.
Vim in Browsers (Vimium-C), even in Jupyter notebooks.

Advanced Vim¶

Search and Replace¶

:s: %s/foo/bar/g to replace foo with bar globally in file. %s/\[.*\]($.*$)/\1/g is to replace named Markdown links with plain URLs.

Macro¶

q{character} to start recording a marcro in register {character}.
q to stop recording.
@{character} replays the macro
- {number}@{character} executes a macro {number} times.
Macros can be recursive.

Example : convert xml to json

File

Record a macro stored in register e to format a single element.
- Go to line with <name>
- qe^r"f>s": "<ESC>f<C"<ESC>q
Record a macro stored in registser p to format a person.
- Go to line with <person>
- qpS{<ESC>j@eA,<ESC>j@ejS},<ESC>q
Record a macro stored in register q to format a person and go to the next person.
- Go to line with <person>
- qq@pjq
Execute macro until end of file.
- 999@q
Manually remove last , and add [ and ] delimiters.

4. Data Wrangling¶

An example runs through this lecture : Wrangle the data from ssh myserver journalctl.

Regular Expressions (Regex)¶

Common patterns¶

. matches any singel character except newline \n or \r.
* zero or more of the preceding match.
+ one or more of the preceding match.
[abc] matches any one character of a, b and c.
(RX1|RX2) either matches RX1 or RX2.
^ the start of the line.
$ the end of the line.
By default, * and + are greedy. Suffix * or + with ? to take it non-greedy.

Capture group¶

Any match of parenthesis will stored in the capture group (unless ?: or other similar patterns are put in the front of the parenthesis). We can use \1, \2 to refer them.

More patterns and details for regex on Regular expression - Wikipedia or 正则表达式 – 教程 | 菜鸟教程.

A nice tool to check regex: regex101: build, test, and debug regex.

sed

sed is a stream editor building on top of the old ed editor. It supports regex for data wrangling.

Mostly used command are s (substitution). Its syntax is s/REGEX/SUBSTITUTION. REGEX is the regular expression, SUBSTITUTION is the text to substitute matching text with.

Regex of sed is a bit weird. It requires a \ before most of the character above to give them special meaning. Or more intuitively, pass -E.

But sed don't support non-greedy mode. Another tool supporting non-greedy is perl -pe.

At the last of these part, regex is used to wrangle data with the following command.

ssh myserver journalctl
| grep sshd
| grep "Disconnected from"
| sed -E 's/.*Disconnected from (invalid |authenticating )?user (.*) [^ ]+ port [0-9]+( \[preauth\])?$/\2/'

Other command for data wrangling¶

sort

By default, it sorts the data with the first column as a key word and ascending lexicographic order.
-n will sort in numeric order.
-r will reverse.
-u will take the unique value.
-k specifies the coloum as a key word.

uniq

filter repetitive lines
-c or --count will show a count of the number of occurrences.
-u will show the lines that only occur once.

wc

count something
-c or --bytes or --chars will show the count of bytes.
-l or --lines will show the count of lines.
-w or --words will show the count of words.

paste

-d<delimiter> or --delimiters=<delimiter> specifies the delimiter.
-s or --serial combines multiple lines into one line.

awk

awk is a programming language that just happens to be good at processing text streams. As with many other things here, only basic wll be gone through.

$0 is set to the entire line. $1 through $n are set to the n-th field of that line, when separated by awk field separator (white space by default, change with -F).
So | awk '{print $2}' will print the second part from STDIN.
Compute the number of single used usernames that match some regex pattern (start with c and end with e) from STDIN: | awk '$1 == 1 && $2 ~ /^c[^ ]*e$/ {print $2}' | wc -l. wc -l is also not needed for it if we rewrite the awk part to awk 'BEGIN {rows = 0} $1 == 1 && $2 ~ /^c[^ ]*e$/ {rows += $1} END {print rows}'. BEGIN and END are patterns that match the start and the end of the input respectively.

ssh myserver journalctl
 | grep sshd
 | grep "Disconnected from"
 | sed -E 's/.*Disconnected from (invalid |authenticating )?user (.*) [^ ]+ port [0-9]+( \[preauth\])?$/\2/'
 | sort | uniq -c
 | sort -nk1,1 | tail -n10
 | awk '{print $2}' | paste -sd,

Analyzing Data¶

bc

A simple caculator which support +-*/^% and sqrt().
Other feature
- set decimal digits: echo 'scale=2; (4.3 - 1.2) / 2' | bc returns 1.55.
- specify base: echo 'ibase=2; 111' | bc returns 7.
- change base : echo 'obase=2; 5 | bc returns 101.

Plot the Data

R language or gnuplot for simpler plot.

ssh myserver journalctl
 | grep sshd
 | grep "Disconnected from"
 | sed -E 's/.*Disconnected from (invalid |authenticating )?user (.*) [^ ]+ port [0-9]+( \[preauth\])?$/\2/'
 | sort | uniq -c
 | sort -nk1,1 | tail -n10
 | gnuplot -p -e 'set boxwidth 0.5; plot "-" using 1:xtic(2) with boxes'

Wrangling Binary Data¶

Notice that - takes the output to STDIN or takes the input from STDIN.

ffmpeg -loglevel panic -i /dev/video0 -frames 1 -f image2 - 
| convert - -colorspace gray -

5. Command-line Environment¶

Job Control¶

Signal¶

Shell uses a UNIX communication mechanism called a signal to communicate information to the process. When a process receives a signal, it stops its execution, deals with the signal and potentially changes the flow of execution. For this reason, signals are software interrupts.

Use man signal or kill -l to learn more about it.

Killing a process¶

Ctrl + C will deliver a SIGINT signal to the process.
Ctrl + \ will deliver a SIGNQUIT signal to the process.

Although SIGINT and SIGQUIT are both usually associated with terminal related requests, a more generic signal for asking a process to exit gracefully is the SIGTERM signal. We can use kill command, with the syntax kill -TERM <PID>.

SIGKILL is a special signal. It cannot be captured by the process and will always terminate it immediately. But it can have bad side effects such as leaving orphaned children processes.

Pausing and backgrouding processes¶

STIGSTOP pauses a process. In the terminal, Ctrl + Z will prompt the shell to send a SIGTSTP signal, short for Terminal Stop. (i.e. the terminal's version of SIGSTOP)

fg and bg can continue the paused job in the foreground or in the background respectively.

Note

To run the program in the background, suffix & with the command. But it will still use the shell's STDOUT, or we can use shell redirections.

To background an already running program, we can do Ctrl + Z and then execute bg. Note the background process are still children processes of the terminal and will die if the terminal will closed. Because closing the terminal sends a SIGHUP signal.

To prevent it, we can run the program with nohup or use disown for the already running program. Or we can use a terminal multiplexer.

Terminal Multiplexers¶

tmux

the config file is ~/.tmux.conf.
a hierarchy of three layers : session, window and pane.
detail in tmux and then press <C-b>?.

Alias, dotfiles and SSH¶

I've learn about it before. So this part is just for some supplements.

Dotfile Version Control¶

It's nice to put all the dotfiles together in a folder with version control. And symbolically link them to its own place.

Execute command directly from ssh device¶

e.g. ssh foobar@server ls will execute ls in the home folder of foobar.

Copy files over SSH¶

ssh + tee
scp
rsync

SSH config¶

Config file is in ~/.ssh/config.

Host vm
    User foobar
    HostName 172.16.174.141
    Port 2222
    IdentityFile ~/.ssh/id_ed25519
    LocalForward 9999 localhost:8888

# wildcards 通配符 are also OK!
Host *.mit.edu
    User foobaz

Shell & Framework and Terminal Emulators¶

zsh is a superset of bash with the following features.

Smarter globbing
Inline globbing
Spelling correction
Better completion/selection
Path expansion

For framework of shell, the following is some attainable features. - Right prompt - Command syntax highlighting - History substring search - Prompt themes

Configuration of terminal emulators¶

A look at terminal emulators

Font
Theme
Keyboard shortcuts
Scrollback
Performance (alacritty of kitty offer GPU acceleration)

6. Version Control (Git)¶

Info

Snapshot

In git terminology, a file is called a blob and a directory is called a tree. A snapshot is the top-level tree that is being tracked.

History Model

In git, a history is a directed acyclic graph (DAG, 有向无环图) of snapshots.

Structure and Model of git¶

All git command line commands are manipulations of either the references data or the objects data.

Pseudo Code of git model

// pseudocode

type blob = array<byte>
type tree = map<string, tree | blob>
type commit = struct {
    parents: array<commit>
    author: string
    message: string
    snapshot: tree
}

type object = blob | tree | commit
objects = map<string, object>
# The key of `objects` is the sha-1 of object, which is a hexadecimal string of 40 characters.

def store(o):
    id = sha1(o)
    object[id] = o

def load(id):
    return object[id]

references = map<string, string>    # <name, sha-1 string>
# Name is immutable but sha-1 string not.

7. Debugging and Profiling¶

Debugging¶

Print debugging and Logging¶

Here is an example code that logs messages.

Color the Log¶

For better readability, we can color them. If the terminal supports true color (真彩色), then echo -e '\e[38;2;255;0;0mThis is read\e[0m' will print out a red message This is red.

The following script shows how to print many RGB colors into the terminal.

#!/usr/bin/env bash
for R in $(seq 0 20 255); do
    for G in $(seq 0 20 255); do
        for B in $(seq 0 20 255); do
            printf "\e[38;2;${R};${G};${B}m█\e[0m";
        done
    done
done

Third party logs¶

System uses a system log, which is increasingly where all log messages go. Most Linux system use systemd. systemd places the logs under /var/log/journal in a specialized format and use journalctl to display the messages.

logger shell program supports logging under the system logs.

Debugger¶

Debuggers are programs that let you interact with the execution of a program.

Many programming languages come with some form of debugger. In Python this is pdb, or ipdb for better performance.

For more low level programming, gdb and lldb may be a good choice.

Even if trying to debug a black box binary, there are tools to help. strace in LInux can trace the system call the program uses.

Static Analysis

Static analysis programs take source code as input and analyze it using coding rules to reason about its correctness.

pyflakes and mypy for python and shellcheck for shell scripts.

Most editors and IDEs support displaying the output of these tools within the editor, highlighting the locations of warning and errors. This is called code linting.

Profiling¶

Timing¶

Real time
- Wall clcok elapsed time from start to finish of the program, including the time taken by other processes and time taken while blocked ( e.g. waiting for I/O or network ).
User time
- Amount of time spent in the CPU running user code.
Sys time
- Amount of time spent in the CPU running kernel code.

Profiler¶

CPU
- Two main types of CPU profilers : tracing and sampling profilers.
  - Tracing profilers keep a record of every function call the program makes.
  - Sampling profilers probe the program periodically and record the program's stack.
- e.g. cProfiler for python.
Memory
- e.g. memory_profiler for python.
Event Profileing

Visualization

For CPU sampling profilers is to use a Flame Graph.

Resource Monitoring

General Monitoring htop
I/O operations iotop
Dis usage df
Memory Usage free
Open Files lsof
Network Connections and Config ss
Network Usage `nethogs and iftop

hyperfine can quickly benchmark command line programs.

8. Metaprogramming¶

Build systems¶

make is one of the most common build systems. It has its warts, but works quite well for simple-to-moderate projects. When we run make, it consult a file called Makefile in the current directory.

Dependency Management¶

Different distros have differnet package manager and repository. But there are some common concepts of them.

Versioning¶

Most projects that other projects depend on issue a version number with every release.

The relatively common standard is semantic versioning. For its rules, every version number is of the form: major.minor.patch.

Increase the patch version, if a new release does not change the API, such as security improvement.
Increase the minor version, if an API is added in a backwards-compatible (向下兼容) way.
Increase the major version, if the API is changed in a non-backwaraeds-compatible way.

Lock File¶

A lock file is simply a file that lists the exact version you are currently depending on of each dependency. Usually, an update program should be run explicitly to upgrade the newer versions of the dependencies.

Continuous Integration Systems¶

Continuous, or CI is an umbrella term for stuff that runs whenever your code changes.

By far the most common one is a rule like 「when someone pushes code, run the test suite」.

9. Security and Cryptography¶

Entropy

Entropy is a measure of randomness. It's useful when determining the strength of a password.

Entropy is measured in bits. When selecting uniformly at random from a set of possible outcomes (均匀分布的随机离散变量), the entropy is equal to $log_2(\text{\# of possibilities})$.

For on-line guessing, around 40 bits of entropy is pretty good. To be resistant to off-line guessing, a stronger password would be necessary (e.g. 80 bits or more).

Hash Function¶

hash(value: array<byte>) -> vector<byte, N> (for some fixed N)

Example

An example is SHA-1, which used in git. It maps arbitrary-sized inputs to 160-bit outputs. We can try out SHA-1 with sha1sum command,

$ printf 'hello' | sha1sum
aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d
$ printf 'hello' | sha1sum
aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d
$ printf 'Hello' | sha1sum
f7ff9e8b7bb2e09b70935a5d785e0cc5d9d0abf0

At a high level, a hash function can be thought of as a hard-to-invert random-looking (but deterministic) function.

Properties

Deterministic 确定性 : the same input always generates the same output.
Non-invertible 不可逆性 : it's hard to find an input m such that hash(m) = h for desired output h.
Target collision resistant 目标碰撞抵抗性（弱无碰撞）: given an input m1, it's hard to find a different input m2, such that hash(m1) = hash(m2).
Collision resistant 碰撞抵抗性（强无碰撞）: it's hard to find two inputs m1 and m2 such that hash(m1) = hash(m2). (strictly stronger than target collision resistant)

Note

Although it may work for certain purpose (like implementing directory by hash table), SHA-1 is no longer considered a strong cryptographic hash function.

Applications

Git, for content-addressed storage 内容寻址存储. Hash function is not only cryptographic, it's used in git to avoid content-address conflict.
Message digest 文件信息摘要. The official sites usually post hashes alongside the download links. Software can be downloaded from mirrors and be checked after downloading the file.
Commitment schemes 承诺机制.

Example

Suppose you want to commit to a particular value, but reveal the value itself later. For example, I want to do a fair coin toss “in my head”, without a trusted shared coin that two parties can see. I could choose a value r = random(), and then share h = sha256(r). Then, you could call heads or tails (we’ll agree that even r means heads, and odd r means tails). After you call, I can reveal my value r, and you can confirm that I haven’t cheated by checking sha256(r) matches the hash I shared earlier.

Key Derivation Functions (KDFs)¶

Properties

Slow : To slow down off-line brute-force attacks.

Applications

Storing login credentials. Generate and store a random salt salt = random() for each user, store KDF(password + salt) and verify by KDF(input + salt).
Producing keys from pass-phrases for use in other cryptographic algorithms.

flowchart LR
    p[passphrase] --> KDF --> k[key] --> encrypt
    pt[plaintext] --> encrypt
    encrypt --> ct[ciphertext]
    style p fill:#FFF, stroke-width:0px
    style k fill:#FFF, stroke-width:0px
    style pt fill:#FFF, stroke-width:0px
    style ct fill:#FFF, stroke-width:0px

Symmetric Cryptography¶

keygen() -> key (this function is randomized)

encrypt(plaintext: array<byte>, key) -> ciphertext: array<byte>
decrypt(ciphertext: array<byte>, key) -> plaintext: array<byte>

An example of a symmetric cryptosystem in wide use today is AES.

$ openssl aes-256-cbc -salt -in note.md -out note.enc.md
enter aes-256-cbc encryption password:
Verifying - enter aes-256-cbc encryption password:
$ openssl aes-256-cbc -d -in note.enc.md -out note.dec.md
enter aes-256-cbc encryption password:
$ cmp note.md note.dec.md
$ echo $?
0

Properties

given ciphertext, it's hard to figure out plaintext without key.
decrypt(encrypt(m, k), k) = m

Applications

Encrypting files for storage in an untrusted cloud service.

Asymmetric Cryptography¶

keygen() -> (public key, private key)

encrypt(plaintext: array<byte>, public key) -> ciphertext: array<byte>
decrypt(ciphertext: array<byte>, private key) -> plaintext: array<byte>

sign(message: array<byte>, private key) -> signature: array<byte>
verify(message: array<byte>, signature: array<byte>, public key) -> bool (the signature is valid or not)

An example of an asymmetric cryptosystem is RSA.

Properties

hard to get plaintext from ciphertext without private key.
decrypt(encrypt(m, k), k) = m

Applications

PGP email encryption.
Private messaging. Apps like Signal or Keybase.
Signing software. Git can have GPG-signed commit and tags. With a posted public key, anyone can verify the authenticity of downloaded software.

Key Distribution

It's a big challenge of distributing public keys / mapping public keys to real-world identities.

Solutions

for Signal : trust on first use, and support out-of-band 线下 public key exchange and safety number 面对面交换公钥.
for PGP : web of trust 信任网络
for Keybase : social proof 社交网络证明

Hybrid Encrytion¶

Sender End¶

flowchart LR
    m[plaintext] --> se[symmetric encryption]
    sk[symmetric keygen] --> key --> se --> ct[ciphertext]
    key --> ae
    pk[public key] --> ae[asymmetric encryption] --> ek[encrypted key]
    style m fill:#FFF, stroke-width:0px
    style key fill:#FFF, stroke-width:0px
    style ct fill:#FFF, stroke-width:0px
    style ek fill:#FFF, stroke-width:0px
    style pk fill:#FFF, stroke-width:0px

Receiver End¶

flowchart LR
    ek[encrypted key] --> ad[asymmetric decryption]
    pk[private key] --> ad[asymmetric decryption] --> key --> sd[symmetric decryption]
    ct[ciphertext] --> sd[symmetric decryption] --> m[plaintext]
    style m fill:#FFF, stroke-width:0px
    style pk fill:#FFF, stroke-width:0px
    style ek fill:#FFF, stroke-width:0px
    style key fill:#FFF, stroke-width:0px
    style ct fill:#FFF, stroke-width:0px

Case Studies

Password managers: KeePassXC, Pass, 1Password
Two-factor authentication
Full disk encryption
- Linux : cryptsetup + LUKS
- Windows : BitLocker
- macOS : FileVault
Private messaging
Signal and Keybase. End-to-end security is bootstrapped from asymmetric-key encryption.
SSH

10 & 11. Pot-pourri and Q&A¶

最后更新: 2023.11.21 17:00:13 CST
创建日期: 2023.01.25 16:27:57 CST

The Missing Semester of Your CS Education¶

1. Course Overview and the Shell¶

2. Shell Tools and Scripting¶

Script¶

Shell Tools¶

Finding Files¶

Finding Code¶

Find Shell Commands¶

Directory Navigation¶

3. Editors (Vim)¶

Vim-mode in other programs¶

Advanced Vim¶

Search and Replace¶

Macro¶

4. Data Wrangling¶

Regular Expressions (Regex)¶

Common patterns¶

Capture group¶

Other command for data wrangling¶

Analyzing Data¶

Wrangling Binary Data¶

5. Command-line Environment¶

Job Control¶

Signal¶

Killing a process¶

Pausing and backgrouding processes¶

Terminal Multiplexers¶

Alias, dotfiles and SSH¶

Dotfile Version Control¶

Execute command directly from ssh device¶

Copy files over SSH¶

SSH config¶

Shell & Framework and Terminal Emulators¶

Configuration of terminal emulators¶

6. Version Control (Git)¶

Structure and Model of git¶

7. Debugging and Profiling¶

Debugging¶

Print debugging and Logging¶

Color the Log¶

Third party logs¶

Debugger¶

Profiling¶

Timing¶

Profiler¶

8. Metaprogramming¶

Build systems¶

Dependency Management¶

Versioning¶

Lock File¶

Continuous Integration Systems¶

9. Security and Cryptography¶

Hash Function¶

Key Derivation Functions (KDFs)¶

Symmetric Cryptography¶

Asymmetric Cryptography¶

Hybrid Encrytion¶

Sender End¶

Receiver End¶

10 & 11. Pot-pourri and Q&A¶