Glossary
What is a private key?
Private keyey is the secret half of a key pair. It creates your digital signatures and must stay under your control, because anyone who holds it can sign as you.
The private key does the signing. It never needs to be shown to anyone, and a well-built system never shows it.
On a phone, the key can live in secure hardware that signs on request and will not hand the key out. Unlocking it with a fingerprint or face adds a second barrier.
Under the Electronic Transactions Act, 2063, a certificate holder must take reasonable care to keep control of the private key and prevent its disclosure.