feat(cipher): add manual OTP decryption instructions and pad generator
- Expand instructions.md with step-by-step manual encryption/decryption example using modular addition. - Add padgen.py script to generate random one-time pads from /dev/urandom, formatted in groups. - Add cleanup of temporary audio file in numbers_station.sh. - Minor title update in site/index.html for clarity.
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Gregory Gauthier
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## HOW TO DECRYPT — STEP BY STEP (using your 8-bit machine)
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### HOW TO DECRYPT — STEP BY STEP (by hand)
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1. Type in the NERDLETTER DECRYPTOR BASIC program (see below)
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1. **Key Generation**
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- You generate a **truly random key** that is **exactly as long as the plaintext message**.
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- The key must be purely random (each bit or character has equal probability and no patterns).
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- The key is shared securely between sender and receiver **in advance** (this is the hard part in practice).
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2. **Encryption**
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- Take the plaintext message.
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- Combine it with the key using a reversible operation. The two most common methods are:
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- **Bitwise XOR** (for binary data — the standard modern way)
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- **Modular addition** (for letters, e.g., A=0, B=1, ..., Z=25 — the classic "pad" method)
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**Example with letters (Vigenère-style addition mod 26):**
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Plaintext: `H E L L O`
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→ Numbers: `7 4 11 11 14`
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One-time pad: `X M C K L`
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→ Numbers: `23 12 2 10 11`
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Ciphertext: `(7+23) (4+12) (11+2) (11+10) (14+11) mod 26`
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→ `4 16 13 21 25`
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→ Letters: `E Q N V Z`
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3. **Decryption**
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- The receiver does the **inverse operation** with the same key.
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- For modular addition: subtract the key (mod 26).
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- For XOR: XOR the ciphertext with the key again (XOR is its own inverse).
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Ciphertext: `E Q N V Z`
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Key: `X M C K L`
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Plaintext: `H E L L O`
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### HOW TO DECRYPT — STEP BY STEP (using your 8-bit machine)
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1. Type in the NERDLETTER DECRYPTOR BASIC program (provided with your subscription)
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2. RUN
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2. RUN
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3. When it asks, type the PAD groups from the appropriate page:
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3. When it asks, type the PAD groups from the appropriate page:
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@ -12,7 +47,7 @@
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5. The machine will instantly print the plaintext!
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5. The machine will instantly print the plaintext!
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## RESULT YOU SHOULD SEE:
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#### RESULT YOU SHOULD SEE:
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```
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```
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MARYHADALITTLELAMB
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MARYHADALITTLELAMB
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34
cipher/padgen.py
Normal file
34
cipher/padgen.py
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#!/usr/bin/env python3
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"""Generate a one-time pad of uppercase letters from /dev/urandom."""
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import sys
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def generate_daybook(weeks: int = 52):
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for week in range(1, weeks + 1):
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with open(f"daybook_week_{week:02d}.txt", "w") as f:
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f.write(f"WEEK {week:02d}\n\n")
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f.write(format_pad(generate_pad(500)))
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def generate_pad(num_letters: int) -> str:
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"""Read raw bytes from /dev/urandom and map them uniformly to A-Z."""
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letters = []
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with open("/dev/urandom", "rb") as f:
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while len(letters) < num_letters:
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b = f.read(1)[0]
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# Reject bytes >= 234 to avoid modulo bias.
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# 234 = 9 * 26, so bytes 0..233 map uniformly to 0..25.
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if b < 234:
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letters.append(chr((b % 26) + 65))
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return "".join(letters)
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def format_pad(text: str, group_size: int = 5, groups_per_line: int = 10) -> str:
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"""Format as 5-letter groups, 10 groups per line — classic OTP layout."""
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groups = [text[i:i + group_size] for i in range(0, len(text), group_size)]
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lines = [" ".join(groups[i:i + groups_per_line])
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for i in range(0, len(groups), groups_per_line)]
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return "\n".join(lines)
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if __name__ == "__main__":
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n = int(sys.argv[1]) if len(sys.argv) > 1 else 500
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print(format_pad(generate_pad(n)))
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@ -119,4 +119,6 @@ drawtext=font='Courier':fontsize=44:fontcolor=lime@0.95:text='${MESSAGE}':x=(w-t
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drawtext=font='Courier':fontsize=30:fontcolor=green@0.75:text='DESTROY PAGE AFTER USE — SUBSCRIBERS ONLY':x=(w-text_w)/2:y=640" \
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drawtext=font='Courier':fontsize=30:fontcolor=green@0.75:text='DESTROY PAGE AFTER USE — SUBSCRIBERS ONLY':x=(w-text_w)/2:y=640" \
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-c:v libx264 -pix_fmt yuv420p -c:a aac -shortest "$OUTFILE" -y
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-c:v libx264 -pix_fmt yuv420p -c:a aac -shortest "$OUTFILE" -y
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rm "${TMPDIR}/final_audio.wav"
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echo "Done: ${OUTFILE}"
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echo "Done: ${OUTFILE}"
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@ -3,7 +3,7 @@
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<head>
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<head>
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<meta charset="UTF-8">
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>The Nerdletter • Retro-Modern Fusion</title>
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<title>The Nerdletter • Retro-Modern Fusion Newsletter</title>
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<style>
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<style>
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@import url('https://fonts.googleapis.com/css2?family=VT323&display=swap'); /* Perfect CRT font */
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@import url('https://fonts.googleapis.com/css2?family=VT323&display=swap'); /* Perfect CRT font */
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body {
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body {
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