Most modern encryption (like Bitcoin, Ethereum, and SSH) uses Elliptic Curve Cryptography (ECC).
- Your Private Key is essentially just a very large random number.
- To get the Public Key, that number is multiplied by a defined “Generator Point” on a specific mathematical curve.
- The result is a set of coordinates $(x, y)$ on that curve, which becomes your Public Key.
Practical Methods to Extract Your Public Key
The method depends on what kind of key you have. Here are the most common ways to do it locally:
1. For SSH Keys
If you have an SSH private key (usually named id_rsa or id_ed25519) and need the .pub file:
- Open your terminal.
Run the following command:
ssh-keygen -y -f /path/to/your/private_key > public_key.pub- This will read the private key and output the corresponding public key into a new file.
2. For OpenSSL (General Encryption)
If your key is in a standard RSA or ECC format (often .pem or .key files):
For RSA keys:
openssl rsa -in private.pem -pubout -out public.pemFor Elliptic Curve (EC) keys:
openssl ec -in private.pem -pubout -out public.pem
openssl ec -in private.pem -pubout -out public.pem3. For Cryptocurrency (Python Example)
If you are trying to find a Bitcoin or Ethereum public key from a hex string, you can use a library like ecdsa. Do not do this if you aren’t comfortable with code.
from ecdsa import SigningKey, SECP256k1
# Replace with your hex private key
private_key_hex = "your_private_key_here"
priv = SigningKey.from_string(bytes.fromhex(private_key_hex), curve=SECP256k1)
pub = priv.get_verifying_key()
print("Public Key (hex):", pub.to_string().hex())
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