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add support for ssh certificates #1486

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48 changes: 43 additions & 5 deletions lib/client.js
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Original file line number Diff line number Diff line change
Expand Up @@ -84,6 +84,7 @@ class Client extends EventEmitter {
username: undefined,
password: undefined,
privateKey: undefined,
certificate: undefined,
tryKeyboard: undefined,
agent: undefined,
allowAgentFwd: undefined,
Expand Down Expand Up @@ -209,6 +210,10 @@ class Client extends EventEmitter {
|| Buffer.isBuffer(cfg.privateKey)
? cfg.privateKey
: undefined);
this.config.certificate = (typeof cfg.certificate === 'string'
|| Buffer.isBuffer(cfg.certificate)
? cfg.certificate
: undefined);
this.config.localHostname = (typeof cfg.localHostname === 'string'
? cfg.localHostname
: undefined);
Expand Down Expand Up @@ -254,6 +259,7 @@ class Client extends EventEmitter {
this._agent = (this.config.agent ? this.config.agent : undefined);
this._remoteVer = undefined;
let privateKey;
let certificate;

if (this.config.privateKey) {
privateKey = parseKey(this.config.privateKey, cfg.passphrase);
Expand All @@ -270,6 +276,24 @@ class Client extends EventEmitter {
}
}

// SSH certificate authentication support (RFC 4252, OpenSSH PROTOCOL.certkeys)
// We store both the parsed certificate (for validation) and the raw string
// (needed by authPK to extract the full certificate blob for transmission)
let certificateRaw;
if (this.config.certificate) {
certificateRaw = this.config.certificate;
certificate = parseKey(this.config.certificate);
if (certificate instanceof Error)
throw new Error(`Cannot parse certificate: ${certificate.message}`);
if (Array.isArray(certificate))
certificate = certificate[0];
if (!certificate.type.includes('-cert-')) {
throw new Error(
'certificate value is not a valid OpenSSH certificate'
);
}
}

let hostVerifier;
if (typeof cfg.hostVerifier === 'function') {
const hashCb = cfg.hostVerifier;
Expand Down Expand Up @@ -388,7 +412,8 @@ class Client extends EventEmitter {
);
return;
case 'publickey':
proto.authPK(curAuth.username, curAuth.key, keyAlgo);
proto.authPK(curAuth.username, curAuth.key, keyAlgo,
undefined, curAuth.certificateRaw);
return;
case 'hostbased':
proto.authHostbased(curAuth.username,
Expand Down Expand Up @@ -471,7 +496,7 @@ class Client extends EventEmitter {
return tryNextAuth();
}
cb(signature);
});
}, curAuth.certificateRaw);
}
},
USERAUTH_INFO_REQUEST: (p, name, instructions, prompts) => {
Expand Down Expand Up @@ -882,7 +907,7 @@ class Client extends EventEmitter {
nextAuth = { type, username, password: this.config.password };
break;
case 'publickey':
nextAuth = { type, username, key: privateKey };
nextAuth = { type, username, key: privateKey, certificate, certificateRaw };
break;
case 'hostbased':
nextAuth = {
Expand Down Expand Up @@ -941,7 +966,19 @@ class Client extends EventEmitter {
return skipAuth('Skipping invalid key auth attempt');
if (!key.isPrivateKey())
return skipAuth('Skipping non-private key');
nextAuth = { type, username, key };
let cert;
let certRaw;
if (nextAuth.certificate) {
certRaw = nextAuth.certificate; // Keep raw string
cert = parseKey(nextAuth.certificate);
if (cert instanceof Error)
return skipAuth('Skipping invalid certificate');
if (Array.isArray(cert))
cert = cert[0];
if (!cert.type.includes('-cert-'))
return skipAuth('Skipping non-certificate');
}
nextAuth = { type, username, key, certificate: cert, certificateRaw: certRaw };
break;
}
case 'hostbased': {
Expand Down Expand Up @@ -1009,7 +1046,8 @@ class Client extends EventEmitter {
);
}
}
proto.authPK(username, curAuth.key, keyAlgo);
proto.authPK(username, curAuth.key, keyAlgo,
undefined, curAuth.certificateRaw);
break;
}
case 'hostbased': {
Expand Down
55 changes: 43 additions & 12 deletions lib/protocol/Protocol.js
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Original file line number Diff line number Diff line change
Expand Up @@ -628,16 +628,41 @@ class Protocol {

sendPacket(this, this._packetRW.write.finalize(packet));
}
authPK(username, pubKey, keyAlgo, cbSign) {
authPK(username, pubKey, keyAlgo, cbSign, certificate) {
if (this._server)
throw new Error('Client-only method called in server mode');

pubKey = parseKey(pubKey);
if (pubKey instanceof Error)
throw new Error('Invalid key');

const keyType = pubKey.type;
pubKey = pubKey.getPublicSSH();
let keyType = pubKey.type;
// For certificate auth, signatures use the underlying key algorithm
// (e.g., 'ssh-ed25519'), not the certificate type
const underlyingKeyType = keyType;
let pubKeyBlob = pubKey.getPublicSSH();

// SSH certificate authentication (OpenSSH PROTOCOL.certkeys)
// When a certificate is provided, we send the full certificate blob
// instead of the raw public key, and use the certificate type
// (e.g., 'ssh-ed25519-cert-v01@openssh.com') as the key algorithm
if (certificate) {
// Parse certificate from OpenSSH format: "type base64-blob [comment]"
let certStr = certificate;
if (Buffer.isBuffer(certificate))
certStr = certificate.toString('utf8');

const certParts = certStr.trim().split(/\s+/);
if (certParts.length < 2)
throw new Error('Invalid certificate format');

keyType = certParts[0];
pubKeyBlob = Buffer.from(certParts[1], 'base64');

// this._debug && this._debug(
// `authPK: certificate auth, type=${keyType}, blobLen=${pubKeyBlob.length}`
// );
}

if (typeof keyAlgo === 'function') {
cbSign = keyAlgo;
Expand All @@ -648,7 +673,7 @@ class Protocol {

const userLen = Buffer.byteLength(username);
const algoLen = Buffer.byteLength(keyAlgo);
const pubKeyLen = pubKey.length;
const pubKeyLen = pubKeyBlob.length;
const sessionID = this._kex.sessionID;
const sesLen = sessionID.length;
const payloadLen =
Expand Down Expand Up @@ -684,7 +709,7 @@ class Protocol {
packet.utf8Write(keyAlgo, p += 4, algoLen);

writeUInt32BE(packet, pubKeyLen, p += algoLen);
packet.set(pubKey, p += 4);
packet.set(pubKeyBlob, p += 4);

if (!cbSign) {
this._authsQueue.push('publickey');
Expand All @@ -697,15 +722,20 @@ class Protocol {
}

cbSign(packet, (signature) => {
signature = convertSignature(signature, keyType);
// For certificate auth, the signature algorithm must be the underlying
// key type (e.g., 'ssh-ed25519'), not the certificate type
signature = convertSignature(signature, underlyingKeyType);
if (signature === false)
throw new Error('Error while converting handshake signature');

const sigLen = signature.length;
const sigAlgo = underlyingKeyType;
const sigAlgoLen = Buffer.byteLength(sigAlgo);

p = this._packetRW.write.allocStart;
packet = this._packetRW.write.alloc(
1 + 4 + userLen + 4 + 14 + 4 + 9 + 1 + 4 + algoLen + 4 + pubKeyLen + 4
+ 4 + algoLen + 4 + sigLen
+ 4 + sigAlgoLen + 4 + sigLen
);

// TODO: simply copy from original "packet" to new `packet` to avoid
Expand All @@ -727,14 +757,15 @@ class Protocol {
packet.utf8Write(keyAlgo, p += 4, algoLen);

writeUInt32BE(packet, pubKeyLen, p += algoLen);
packet.set(pubKey, p += 4);
packet.set(pubKeyBlob, p += 4);

writeUInt32BE(packet, 4 + algoLen + 4 + sigLen, p += pubKeyLen);
// Signature blob uses underlying key algorithm, not certificate type
writeUInt32BE(packet, 4 + sigAlgoLen + 4 + sigLen, p += pubKeyLen);

writeUInt32BE(packet, algoLen, p += 4);
packet.utf8Write(keyAlgo, p += 4, algoLen);
writeUInt32BE(packet, sigAlgoLen, p += 4);
packet.utf8Write(sigAlgo, p += 4, sigAlgoLen);

writeUInt32BE(packet, sigLen, p += algoLen);
writeUInt32BE(packet, sigLen, p += sigAlgoLen);
packet.set(signature, p += 4);

// Servers shouldn't send packet type 60 in response to signed publickey
Expand Down