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Re: an small question about RSA algorithm
If e = 1, then the ciphertext is the same as the plaintext, making the algorithm useless.
It's required that e is coprime to φ(n) = (p - 1)(q - 1), so that there exists d such that ed = 1 mod φ(n). However, if p and q are distinct primes, then one of them is odd, so φ(n) is even. Thus e can't be 2.
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