Asymmetric Keys: Private Key Security & Public Key Visibility

TL;DR

No, you can’t securely share your private key and hide your public key with asymmetric encryption. Sharing the private key defeats the purpose of asymmetric cryptography. Your public key needs to be publicly available for others to encrypt messages for you.

Understanding Asymmetric Encryption

Asymmetric encryption (also known as public-key cryptography) uses a pair of keys: a private key and a public key. Think of it like this:

• Public Key: A lock anyone can use to secure a box.
• Private Key: The only key that opens the box locked with your public key.

Here’s what each key does:

• Encryption: Anyone can use your public key to encrypt a message.
• Decryption: Only you, with your private key, can decrypt that message.

Why Sharing Your Private Key is a Disaster

1. Compromised Security: If someone else has your private key, they can read all messages encrypted for you. They can also forge digital signatures as if they were you.
2. No More Trust: Asymmetric encryption relies on the secrecy of the private key. Sharing it breaks that trust entirely.

Imagine giving everyone a copy of your house key! That’s what sharing your private key is like.

Why Your Public Key Needs to Be Public

1. Encryption Requirement: People need your public key to encrypt messages they want only you to read. If they can’t get it, they can’t send you secure communications.
2. Verification of Identity: Your public key is often used to verify digital signatures. Others use it to confirm that a message genuinely came from you.

Think about the lock and box analogy again. If nobody has the lock (your public key), they can’t secure anything for you.

How to Securely Distribute Your Public Key

Instead of trying to hide your public key, focus on making sure it’s distributed securely and verifying its authenticity:

1. Public Key Infrastructure (PKI): Use a trusted Certificate Authority (CA) to issue a digital certificate for your public key. This verifies that the key belongs to you.
2. Key Servers: Publish your public key on a well-known key server. These servers help others find and verify your key.
3. Web of Trust: In systems like PGP, rely on a network of trusted individuals to sign each other’s keys.
4. Out-of-Band Verification: Share your public key through a separate, secure channel (e.g., in person or via a verified email) and have others verify it independently. For example:
   • Fingerprint Comparison: Get the fingerprint of your public key (a short hash value). Share this fingerprint with someone you trust through a different communication method. They can then compare it to the fingerprint of the key they receive from you directly.

   gpg --fingerprint [email protected]

In Summary

Asymmetric encryption’s strength lies in keeping the private key secret and making the public key accessible. Trying to hide the public key undermines the entire system. Focus on secure distribution methods instead.