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Asked: 2026-05-11T11:31:47+00:00

From whatever little I understand by reading various material, public-private key pair are the

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From whatever little I understand by reading various material, public-private key pair are the basis of asymmetric encryption and also something about choosing 2 prime numbers (which is roughly your private key) and multiplying them (which is roughly your public key). It appears to me that it is possible to generate a public key if you know the private key. Is it correct or I am mistaking something?

What made me more confusing was that it is not possible to serialize the RSA key to XML with only private key (using .NET class RSACryptoServiceProvider). Not sure whether this limitation is intentional or not!

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  1. That depends on the crypto system.

    In RSA, we have (citing Wikipedia):

    The public key consists of the modulus n and the public (or encryption) exponent e. The private key consists of the modulus n and the private (or decryption) exponent d which must be kept secret.

    Now if we have n and d (the private key), we are only missing e for the public key. But e is often fairly small (less than three digits), or even fixed (a common value is 65537). In these cases getting the public key is trivial.

    For Elliptic Curve Diffie-Hellman, the private key is d, and the public key dG (with G also public), so it’s trivial as well.

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