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Add FIDO/U2F Security Key (SK) support #1496

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Add FIDO/U2F Security Key (SK) support #1496

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79591aa
feat: add support for security keys
MathiasDPX May 15, 2026
d18489a
fix: ed25519 keygen parsing for Node 22 PKCS#8 output
MathiasDPX May 15, 2026
6c037f3
fix: correct SK signature slicing in auth handlers
MathiasDPX May 15, 2026
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4 changes: 4 additions & 0 deletions .github/workflows/ci.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,10 @@ jobs:
uses: actions/setup-node@v4
with:
node-version: ${{ matrix.node-version }}
- name: Install Python 3.11
uses: actions/setup-python@v5
with:
python-version: '3.11'
- name: Check Node.js version
run: node -pe process.versions
- name: Check npm version
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14 changes: 13 additions & 1 deletion lib/keygen.js
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Expand Up @@ -311,7 +311,19 @@ function parseDERs(keyType, pub, priv) {
// - Attributes (absent)

reader = new Ber.Reader(reader.readString(Ber.OctetString, true));
const privBin = reader.readString(Ber.OctetString, true);
let privBin = reader.readString(Ber.OctetString, true);
if (privBin.length !== 32) {
if (privBin.length === 64
&& privBin.subarray(32).equals(pubBin)) {
privBin = privBin.subarray(0, 32);
} else if (privBin.length > 2
&& privBin[0] === 0x04
&& privBin[1] + 2 === privBin.length) {
privBin = privBin.subarray(2);
}
}
if (privBin.length !== 32)
throw new Error('Malformed ED25519 private key');

/*
OpenSSH ed25519 private key:
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5 changes: 5 additions & 0 deletions lib/protocol/constants.js
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Expand Up @@ -73,7 +73,12 @@ if (eddsaSupported)
DEFAULT_SERVER_HOST_KEY.unshift('ssh-ed25519');
const SUPPORTED_SERVER_HOST_KEY = DEFAULT_SERVER_HOST_KEY.concat([
'ssh-dss',
// FIDO/U2F security keys (e.g. YubiKey). Not enabled by default for
// host keys (rare in practice) but recognized for client publickey auth.
'sk-ecdsa-sha2-nistp256@openssh.com',
]);
if (eddsaSupported)
SUPPORTED_SERVER_HOST_KEY.push('sk-ssh-ed25519@openssh.com');


const canUseCipher = (() => {
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4 changes: 2 additions & 2 deletions lib/protocol/handlers.misc.js
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Expand Up @@ -258,7 +258,7 @@ module.exports = {
if (signature !== undefined) {
if (signature.length > (4 + keyAlgo.length + 4)
&& signature.utf8Slice(4, 4 + keyAlgo.length) === keyAlgo) {
// Skip algoLen + algo + sigLen
// Skip algoLen + algo + sigLen (leave the sigblob intact)
signature = bufferSlice(signature, 4 + keyAlgo.length + 4);
}

Expand Down Expand Up @@ -320,7 +320,7 @@ module.exports = {
if (signature !== undefined) {
if (signature.length > (4 + keyAlgo.length + 4)
&& signature.utf8Slice(4, 4 + keyAlgo.length) === keyAlgo) {
// Skip algoLen + algo + sigLen
// Skip algoLen + algo + sigLen (leave the sigblob intact)
signature = bufferSlice(signature, 4 + keyAlgo.length + 4);
}

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