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3

Short Answer: NO, it is not safe, do NOT do this. Longer Answer: You are true that you can use your RSA keypair for both operations. This approach is used in many applications and scenarios. There are Web Services or Single Sign-On implementations, which enforce you to use the same key pair for both operations. X.509 certificates do not allow you (by ...

2

We don't say this can't happen, we just say it won't happen. The only value that will decrypt to $p_2$ under $(e_2,n_2)$ is $p_2^{d_2}$, which we can call $s_2$. So, your problem comes down to asking what is the probability that $s_1=s_2$? If we assume that they're random, and that the moduli are similar enough sizes that this is even a realistic ...

1

If you use the raw RSA operation ($M^d \bmod n$ or $M^e \bmod n$), then no, it is unsafe to use the same key, because an attacker could trick the private key holder into signing a message $M$ (i.e. generating $M^d$) which is actually an encrypted message ($M = P^e$), thus allowing the attacker to recover the original plaintext ($(P^e)^d = P$). (The dual ...

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