On-card key generation.
Creating an OpenPGP keypair directly on a hardware security key — a YubiKey, a Token2 — so the private key is born on the card and never touches the computer or phone. Sometimes called "born on card."
On-card key generation is when the random keypair is computed by the smartcard's own secure element rather than by the host. The private key material is created inside the card and is never exportable — only the public key and on-card operations (sign, decrypt) leave the device.
What it is.
A hardware OpenPGP key can hold a private key in two ways. You can generate a key elsewhere and import it onto the card, or you can ask the card to generate the key itself. The second path is on-card generation: the secure element produces the random key internally and stores it where it can never be read back out.
The difference matters for the threat model. An imported key existed, however briefly, as bytes on a computer or phone — somewhere it could in principle have been copied. A key born on the card has no such window: there is no off-card copy, ever, because the private half is never emitted.
Why it matters.
Non-extractability is the strongest version of the hardware-key promise. For a high-value identity — a maintainer's release key, a journalist's source key — "the private key has never left this token, not even at creation" is a meaningfully stronger statement than "the private key lives on this token now." A seized or compromised host has nothing to surrender.
The cost is symmetrical: a born-on-card key cannot be backed up. If the card fails, is lost, or is reset, the key is gone and so is anything encrypted only to it. Choose on-card generation when you specifically want non-extractability; choose on-device generation with an encrypted backup when recoverability matters more.
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