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upstream: document ed25519-sk pubkey, private key and certificate

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OpenBSD-Commit-ID: 795a7c1c80315412e701bef90e31e376ea2f3c88
This commit is contained in:
djm@openbsd.org 2019-11-18 04:34:47 +00:00 committed by Damien Miller
parent 71856e1142
commit 1306643448
1 changed files with 40 additions and 5 deletions
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45
PROTOCOL.u2f
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@ -36,15 +36,18 @@ in conjunction with a small per-device secret that is unique to the
hardware, thus requiring little on-device storage for an effectively
unlimited number of supported keys. This drives the requirement that
the key handle be supplied for each signature operation. U2F tokens
primarily use ECDSA signatures in the NIST-P256 field.
primarily use ECDSA signatures in the NIST-P256 field, though the FIDO2
standard specified additional key types include one based on Ed25519.
SSH U2F Key formats
-------------------
OpenSSH integrates U2F as a new key and corresponding certificate type:
OpenSSH integrates U2F as new key and corresponding certificate types:
sk-ecdsa-sha2-nistp256@openssh.com
sk-ecdsa-sha2-nistp256-cert-v01@openssh.com
sk-ssh-ed25519@openssh.com
sk-ssh-ed25519-cert-v01@openssh.com
These key types are supported only for user authentication with the
"publickey" method. They are not used for host-based user authentication
@ -72,7 +75,22 @@ The corresponding private key contains:
string key_handle
string reserved
The certificate form of a SSH U2F key appends the usual certificate
The format of a sk-ssh-ed25519@openssh.com public key is:
string "sk-ssh-ed25519@openssh.com"
string public key
string application (user-specified, but typically "ssh:")
With a private half consisting of:
string "sk-ssh-ed25519@openssh.com"
string public key
string application (user-specified, but typically "ssh:")
uint32 flags
string key_handle
string reserved
The certificate form for SSH U2F keys appends the usual certificate
information to the public key:
string "sk-ecdsa-sha2-nistp256-cert-v01@openssh.com"
@ -92,6 +110,22 @@ information to the public key:
string signature key
string signature
string "sk-ssh-ed25519-cert-v01@openssh.com"
string nonce
string public key
string application
uint64 serial
uint32 type
string key id
string valid principals
uint64 valid after
uint64 valid before
string critical options
string extensions
string reserved
string signature key
string signature
During key generation, the hardware also returns attestation information
that may be used to cryptographically prove that a given key is
hardware-backed. Unfortunately, the protocol required for this proof is
@ -187,8 +221,9 @@ OpenSSH integration
U2F tokens may be attached via a number of means, including USB and NFC.
The USB interface is standardised around a HID protocol, but we want to
be able to support other transports as well as dummy implementations for
regress testing. For this reason, OpenSSH shall perform all U2F operations
via a dynamically-loaded middleware library.
regress testing. For this reason, OpenSSH shall support a dynamically-
loaded middleware libraries to communicate with security keys, but offer
support for the common case of USB HID security keys internally.
The middleware library need only expose a handful of functions: