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ProfAvery/rsa.py

Last active October 21, 2025 04:19
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Toy RSA implementation (Understanding Cryptography, Second Edition, pp. 206-208)
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rsa.py
#!/usr/bin/env python3
import math, random
# RSA Key Generation, p. 208
p = int(input("p? "))
q = int(input("q? "))
n = p * q
phi = (p - 1) * (q - 1)
e = random.choice([e for e in range(1, phi) if math.gcd(e, phi) == 1])
d = next(iter([d for d in range(1, phi) if ((d * e) % phi) == 1]))
k_pub = (n, e)
k_pr = d
print(f"{k_pub = }, {k_pr = }")
# RSA Encryption (7.1), p. 206
x = int(input("x? "))
y = pow(x, e, n)
print(f"{y = }")
# RSA Decryption (7.2), p. 207
print(f"pow({y}, {d}, {n}) = {pow(y, d, n)}")
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