# Find the private key when you know the public key

Public Key Encryption: If you have access to the public keys n and e, it is possible to reverse the public keys from them. One approach is to factor the value of n to discover p and q, then to determine d by finding a value k such that k(p-1)(q-1) + 1 divides evenly by e, the quotient being d.

If you have n = 77 and e = 7 for public keys, what are the private keys (n and d)?

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https://brainmass.com/computer-science/data-encryption/finding-private-public-key-542296

#### Solution Preview

Answer:

First, we need to factor n=77. For 77, there are only 2 prime factors of 77: 7 and 11. So let p=7 and q=11. You can also let ...

#### Solution Summary

The solution gives detailed steps on finding the private key when you know the public key using an example.

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