168 lines
4.8 KiB
Markdown
168 lines
4.8 KiB
Markdown
# Tasks for beginners
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This document contains some tasks for Python beginners. It does not aim to teach general
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programming techniques, only how to use Python. I try to avoid unrealistic tasks.
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In case you have somehow gotten this document from another source,
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[this](https://git.cscherr.de/PlexSheep/py-basic/src/branch/master/Tasks.md) is the original
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source, where the links should hopefully work. If something does not work feel free to contact
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me at [software@cscherr.de](mailto:admin@cscherr.de).
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## MD5 Hashchecker
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### Produce a single MD5 Hash
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Difficulty: 1/5
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1. Hash the string `foobar19` with the MD5 hashing algorithm.
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<details>
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<summary>Hints</summary>
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- Use Pythons `hashlib`.
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- Your hashing function does not take strings for input, only raw data (bytes).
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- You need to explicitly tell your hash to actually process the input.
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- When printing your results, the result may be interpreted as data for characters.
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You want the numeric value of the result in Hexadecimal.
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</details>
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<details>
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<summary>Solution</summary>
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The MD5 hash of `foobar19` is `fa5c65d5438f849387d3fdda2be4dd65`.
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[Example Code](src/md5.py)
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</details>
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### Hash multiple values and search for specific ones.
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Difficulty: 2/5
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1. Find a way to produce strings with the basis `foobar` with appended numbers from `000000` to
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`999999`.
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```text
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1. `foobar000000`
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2. `foobar000001`
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3. `foobar000002`
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...
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999998. `foobar999998`
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999999. `foobar999999`
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```
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2. Hash all these with the MD5 hashing algorithm.
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3. Find the exact numbers, how many of these hashes start with `00`
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4. **Bonus**:
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1. If MD5 was a good / perfect Hashing algorithm (it is definitely not),
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how many matches for a `00` prefix should exist? Why?
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2. How many matches for $0$ to $50000$? How many matches for $0$ to $50.000.000$?
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<details>
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<summary>Testvectors</summary>
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Last 5 Matches
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```text
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999384 | 009671fd23fa783df1fff63516e5d115
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999751 | 00ec2ade58f75c44b7300294497f7fb1
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999844 | 009cfd7949b577a3311d9db3ee49c15d
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999852 | 006fe04f7d3f710f93d3e6324506154a
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999902 | 00c063364ddffa1bdf338dfcf0319424
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```
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</details>
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<details>
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<summary>Hints</summary>
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- Use a for loop to do the thing X times
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- Use Pythons string formatting to put the numbers and string together
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- Use Options for the `%d` Placeholder to get $0$ to be displayed as `000000`
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- After hashing, check if your current hash matches the search.
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Print it if that is the case to see if the match is a false positive.
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- Increment a number on each match. The value of that number after the loop is how many
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Hashes start with `00` for this task.
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</details>
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<details>
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<summary>Solution</summary>
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There are 3889 hashes for `foobar000000` to `foobar999999` that start with `00`.
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[Code Example](src/md5range.py)
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**Bonus**
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We want $N/16^2$ occurrences for an ideal hashing algorithm, where $N$ is the maximum of our range
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$+ 1$.
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$16^2$ comes from $2$ characters in a range of `0` to `e` (Hexadecimal).
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We want the hashing algorithm to spread out as much as possible, no value should be more common
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than any other value. This is essential for the security of the hashing algorithm.
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| Value | Ideal Occurences |
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|--------------|------------------|
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| $1.000.000$ | $\approx 3906$ |
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| $500.000$ | $\approx 1953$ |
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| $50.000.000$ | $\approx 195312$ |
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</details>
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### Find earliest hash that fits criteria
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Difficulty: 2/5
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1. Find the earliest integer $X$ for `foobarXXXXXX` (where $X$ is an iterator as in the last
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subtask) that starts with `2718`.
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<details>
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<summary>Hints</summary>
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- You can reuse most code from the last subtask.
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- Match against the new prefix, but stop when you find it.
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- Display the index number in each loop iteration.
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</details>
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<details>
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<summary>Solution</summary>
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The first hash with prefix `2718` occurs at $i=70559$.
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```text
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070559 | 2718e5ee6d05091ce6dad023e55ee19c
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```
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[Code Example](src/md5range-4.py)
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</details>
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## Super basic web server
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Difficulty: 3/5
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1. Program a Python web server that writes "Python is not so hard" in your Browser (or in `cURL`).
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Use `http.server`.
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<details>
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<summary>Hints</summary>
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- Use `http.server.SimpleHTTPRequestHandler` and `io.BytesIO`.
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- Define your own class that inherits `SimpleHTTPRequestHandler`.
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- You don't need to implement `do_GET()`.
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- Implement your own `send_head()` method. This is the method that writes your response (not
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completely on it's own, but unless you feel like inspecting standard libraries, just do what
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I'm saying.).
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- `send_head()` should take no arguments (other than `self`) and return some readable buffer.
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- Don't forget to set the headers for HTTP before sending the body.
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- Your OS might block hosting to ports < 1000. Try to host your web server to `localhost:8080`.
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</details>
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<details>
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<summary>Solution</summary>
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Take a look at the provided Code Example.
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[Code Example](src/miniweb.py)
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</details>
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