privatekey:
Private key that occurs in asymmetric cryptography algorithms such as RSA and Diffie-Hellman as the counterpart to a public key. The private key must never be divulged while the public key can be made available to everyone. If your question is not pertaining specifically to the private key (usage/encoding/etc.), you should use more appropriate tags such as [public-key-encryption], [digital-signature], [diffie-hellman] or even [cryptography].