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39 lines
923 B
Markdown
39 lines
923 B
Markdown
# Challenge 6: Digital Signature Forgery
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**Level:** Advanced
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**Description:**
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Provide a digital signature scheme with a weakness (e.g., using a small prime number). Forge a digital signature for a new message.
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**Challenge Text:**
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```
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Signature scheme: RSA with n = 391, e = 3, d = 107
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Signed message: ("HELLO", signature = 220)
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Challenge: Forge a signature for the message "WORLD"
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```
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**Instructions:**
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1. Understand the weakness in the provided RSA signature scheme.
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2. Forge a signature for the new message.
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3. Validate the forged signature.
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**Answer:**
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For the message "WORLD," a forged signature could be 115.
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**Code:**
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```python
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n = 391
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e = 3
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message = "WORLD"
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# Compute numeric representation of message
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message_numeric = sum([ord(c) * (256 ** i) for i, c in enumerate(message[::-1])])
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# Compute forged signature
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forged_signature = message_numeric ** e % n
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print("Forged signature:", forged_signature)
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```
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