135cf1ff01
- 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.
59 lines
1.9 KiB
Markdown
59 lines
1.9 KiB
Markdown
### HOW TO DECRYPT — STEP BY STEP (by hand)
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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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3. When it asks, type the PAD groups from the appropriate page:
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`VLGKU` then `JXCYH` then `LYMDC` then `ETLUB`
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4. Then type the CIPHERTEXT groups:
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`HLXIB` then `JACJP` then `ERXHN` then `EFM`
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5. The machine will instantly print the plaintext!
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#### RESULT YOU SHOULD SEE:
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```
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MARYHADALITTLELAMB
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```
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(Add spaces by hand: “Mary had a little lamb”)
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This is perfect secrecy — no computer on Earth can read it without this exact Day Book page.
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