A private key is the secret half of a public-key cryptographic pair. Its owner must protect it, while the associated public key can be shared. Depending on the primitive, the private key helps derive a shared secret, decrypt messages, or create signatures. section 1.4.1 section 1.4.2 section 1.4.3
Private keys support several distinct asymmetric-cryptography operations:
- Key exchange: combine your private key with a peer’s public key to derive the same shared secret the peer obtains with the reciprocal pair. section 5.1
- Asymmetric encryption: decrypt ciphertext created by anyone using the corresponding public key; decryption can fail for incoherent ciphertext. section 6.1
- Digital signatures: sign a message so others can verify it with the public key, message, and signature. section 1.4.3
- Asset control: sign transactions to authorize spending associated with the public key, making private-key security central to protecting funds. section 12.2.1
Sending and signing
A sender encrypts a message with a recipient’s public key; only the recipient’s associated private key should decrypt it. Separately, a signer uses a private key to produce a signature, which anyone can verify with the public key and original message. Sharing the public key does not reveal the private key. section 1.4.2 section 1.4.3
A private key does not by itself authenticate the public key received from another party. An unauthenticated key exchange can remain vulnerable to an active man-in-the-middle attacker, who impersonates both participants. section 5.1
