Final answer:
Private keys are stored securely in a Key Store. For Certificate Authorities, the private keys are stored in a Hardware Security Module (HSM). For end-users, private keys are stored on their devices or can be stored in hardware devices like USB tokens or smart cards.
Step-by-step explanation:
Private keys are cryptographic keys that are used in public key cryptography. The private keys are stored in a secure location known as the Key Store. In the case of a Certificate Authority (CA), the private keys are stored securely in a Hardware Security Module (HSM) or a specialized key storage device.
For end-users, the private keys are typically stored on their devices. It is common for web browsers to have a built-in key store where the private keys are stored securely. Additionally, end-users can also store their private keys in a dedicated hardware device such as a USB token or a smart card.