Added export_allowed file to make repository visible in cgit

1 files changed, 752 insertions, 0 deletions

diff --git a/node_modules/sshpk/lib/formats/x509.js b/node_modules/sshpk/lib/formats/x509.js
new file mode 100644
index 0000000..0144c44
--- /dev/null
+++ b/node_modules/sshpk/lib/formats/x509.js
@@ -0,0 +1,752 @@
+// Copyright 2017 Joyent, Inc.
+
+module.exports = {
+	read: read,
+	verify: verify,
+	sign: sign,
+	signAsync: signAsync,
+	write: write
+};
+
+var assert = require('assert-plus');
+var asn1 = require('asn1');
+var Buffer = require('safer-buffer').Buffer;
+var algs = require('../algs');
+var utils = require('../utils');
+var Key = require('../key');
+var PrivateKey = require('../private-key');
+var pem = require('./pem');
+var Identity = require('../identity');
+var Signature = require('../signature');
+var Certificate = require('../certificate');
+var pkcs8 = require('./pkcs8');
+
+/*
+ * This file is based on RFC5280 (X.509).
+ */
+
+/* Helper to read in a single mpint */
+function readMPInt(der, nm) {
+	assert.strictEqual(der.peek(), asn1.Ber.Integer,
+	    nm + ' is not an Integer');
+	return (utils.mpNormalize(der.readString(asn1.Ber.Integer, true)));
+}
+
+function verify(cert, key) {
+	var sig = cert.signatures.x509;
+	assert.object(sig, 'x509 signature');
+
+	var algParts = sig.algo.split('-');
+	if (algParts[0] !== key.type)
+		return (false);
+
+	var blob = sig.cache;
+	if (blob === undefined) {
+		var der = new asn1.BerWriter();
+		writeTBSCert(cert, der);
+		blob = der.buffer;
+	}
+
+	var verifier = key.createVerify(algParts[1]);
+	verifier.write(blob);
+	return (verifier.verify(sig.signature));
+}
+
+function Local(i) {
+	return (asn1.Ber.Context | asn1.Ber.Constructor | i);
+}
+
+function Context(i) {
+	return (asn1.Ber.Context | i);
+}
+
+var SIGN_ALGS = {
+	'rsa-md5': '1.2.840.113549.1.1.4',
+	'rsa-sha1': '1.2.840.113549.1.1.5',
+	'rsa-sha256': '1.2.840.113549.1.1.11',
+	'rsa-sha384': '1.2.840.113549.1.1.12',
+	'rsa-sha512': '1.2.840.113549.1.1.13',
+	'dsa-sha1': '1.2.840.10040.4.3',
+	'dsa-sha256': '2.16.840.1.101.3.4.3.2',
+	'ecdsa-sha1': '1.2.840.10045.4.1',
+	'ecdsa-sha256': '1.2.840.10045.4.3.2',
+	'ecdsa-sha384': '1.2.840.10045.4.3.3',
+	'ecdsa-sha512': '1.2.840.10045.4.3.4',
+	'ed25519-sha512': '1.3.101.112'
+};
+Object.keys(SIGN_ALGS).forEach(function (k) {
+	SIGN_ALGS[SIGN_ALGS[k]] = k;
+});
+SIGN_ALGS['1.3.14.3.2.3'] = 'rsa-md5';
+SIGN_ALGS['1.3.14.3.2.29'] = 'rsa-sha1';
+
+var EXTS = {
+	'issuerKeyId': '2.5.29.35',
+	'altName': '2.5.29.17',
+	'basicConstraints': '2.5.29.19',
+	'keyUsage': '2.5.29.15',
+	'extKeyUsage': '2.5.29.37'
+};
+
+function read(buf, options) {
+	if (typeof (buf) === 'string') {
+		buf = Buffer.from(buf, 'binary');
+	}
+	assert.buffer(buf, 'buf');
+
+	var der = new asn1.BerReader(buf);
+
+	der.readSequence();
+	if (Math.abs(der.length - der.remain) > 1) {
+		throw (new Error('DER sequence does not contain whole byte ' +
+		    'stream'));
+	}
+
+	var tbsStart = der.offset;
+	der.readSequence();
+	var sigOffset = der.offset + der.length;
+	var tbsEnd = sigOffset;
+
+	if (der.peek() === Local(0)) {
+		der.readSequence(Local(0));
+		var version = der.readInt();
+		assert.ok(version <= 3,
+		    'only x.509 versions up to v3 supported');
+	}
+
+	var cert = {};
+	cert.signatures = {};
+	var sig = (cert.signatures.x509 = {});
+	sig.extras = {};
+
+	cert.serial = readMPInt(der, 'serial');
+
+	der.readSequence();
+	var after = der.offset + der.length;
+	var certAlgOid = der.readOID();
+	var certAlg = SIGN_ALGS[certAlgOid];
+	if (certAlg === undefined)
+		throw (new Error('unknown signature algorithm ' + certAlgOid));
+
+	der._offset = after;
+	cert.issuer = Identity.parseAsn1(der);
+
+	der.readSequence();
+	cert.validFrom = readDate(der);
+	cert.validUntil = readDate(der);
+
+	cert.subjects = [Identity.parseAsn1(der)];
+
+	der.readSequence();
+	after = der.offset + der.length;
+	cert.subjectKey = pkcs8.readPkcs8(undefined, 'public', der);
+	der._offset = after;
+
+	/* issuerUniqueID */
+	if (der.peek() === Local(1)) {
+		der.readSequence(Local(1));
+		sig.extras.issuerUniqueID =
+		    buf.slice(der.offset, der.offset + der.length);
+		der._offset += der.length;
+	}
+
+	/* subjectUniqueID */
+	if (der.peek() === Local(2)) {
+		der.readSequence(Local(2));
+		sig.extras.subjectUniqueID =
+		    buf.slice(der.offset, der.offset + der.length);
+		der._offset += der.length;
+	}
+
+	/* extensions */
+	if (der.peek() === Local(3)) {
+		der.readSequence(Local(3));
+		var extEnd = der.offset + der.length;
+		der.readSequence();
+
+		while (der.offset < extEnd)
+			readExtension(cert, buf, der);
+
+		assert.strictEqual(der.offset, extEnd);
+	}
+
+	assert.strictEqual(der.offset, sigOffset);
+
+	der.readSequence();
+	after = der.offset + der.length;
+	var sigAlgOid = der.readOID();
+	var sigAlg = SIGN_ALGS[sigAlgOid];
+	if (sigAlg === undefined)
+		throw (new Error('unknown signature algorithm ' + sigAlgOid));
+	der._offset = after;
+
+	var sigData = der.readString(asn1.Ber.BitString, true);
+	if (sigData[0] === 0)
+		sigData = sigData.slice(1);
+	var algParts = sigAlg.split('-');
+
+	sig.signature = Signature.parse(sigData, algParts[0], 'asn1');
+	sig.signature.hashAlgorithm = algParts[1];
+	sig.algo = sigAlg;
+	sig.cache = buf.slice(tbsStart, tbsEnd);
+
+	return (new Certificate(cert));
+}
+
+function readDate(der) {
+	if (der.peek() === asn1.Ber.UTCTime) {
+		return (utcTimeToDate(der.readString(asn1.Ber.UTCTime)));
+	} else if (der.peek() === asn1.Ber.GeneralizedTime) {
+		return (gTimeToDate(der.readString(asn1.Ber.GeneralizedTime)));
+	} else {
+		throw (new Error('Unsupported date format'));
+	}
+}
+
+function writeDate(der, date) {
+	if (date.getUTCFullYear() >= 2050 || date.getUTCFullYear() < 1950) {
+		der.writeString(dateToGTime(date), asn1.Ber.GeneralizedTime);
+	} else {
+		der.writeString(dateToUTCTime(date), asn1.Ber.UTCTime);
+	}
+}
+
+/* RFC5280, section 4.2.1.6 (GeneralName type) */
+var ALTNAME = {
+	OtherName: Local(0),
+	RFC822Name: Context(1),
+	DNSName: Context(2),
+	X400Address: Local(3),
+	DirectoryName: Local(4),
+	EDIPartyName: Local(5),
+	URI: Context(6),
+	IPAddress: Context(7),
+	OID: Context(8)
+};
+
+/* RFC5280, section 4.2.1.12 (KeyPurposeId) */
+var EXTPURPOSE = {
+	'serverAuth': '1.3.6.1.5.5.7.3.1',
+	'clientAuth': '1.3.6.1.5.5.7.3.2',
+	'codeSigning': '1.3.6.1.5.5.7.3.3',
+
+	/* See https://github.com/joyent/oid-docs/blob/master/root.md */
+	'joyentDocker': '1.3.6.1.4.1.38678.1.4.1',
+	'joyentCmon': '1.3.6.1.4.1.38678.1.4.2'
+};
+var EXTPURPOSE_REV = {};
+Object.keys(EXTPURPOSE).forEach(function (k) {
+	EXTPURPOSE_REV[EXTPURPOSE[k]] = k;
+});
+
+var KEYUSEBITS = [
+	'signature', 'identity', 'keyEncryption',
+	'encryption', 'keyAgreement', 'ca', 'crl'
+];
+
+function readExtension(cert, buf, der) {
+	der.readSequence();
+	var after = der.offset + der.length;
+	var extId = der.readOID();
+	var id;
+	var sig = cert.signatures.x509;
+	if (!sig.extras.exts)
+		sig.extras.exts = [];
+
+	var critical;
+	if (der.peek() === asn1.Ber.Boolean)
+		critical = der.readBoolean();
+
+	switch (extId) {
+	case (EXTS.basicConstraints):
+		der.readSequence(asn1.Ber.OctetString);
+		der.readSequence();
+		var bcEnd = der.offset + der.length;
+		var ca = false;
+		if (der.peek() === asn1.Ber.Boolean)
+			ca = der.readBoolean();
+		if (cert.purposes === undefined)
+			cert.purposes = [];
+		if (ca === true)
+			cert.purposes.push('ca');
+		var bc = { oid: extId, critical: critical };
+		if (der.offset < bcEnd && der.peek() === asn1.Ber.Integer)
+			bc.pathLen = der.readInt();
+		sig.extras.exts.push(bc);
+		break;
+	case (EXTS.extKeyUsage):
+		der.readSequence(asn1.Ber.OctetString);
+		der.readSequence();
+		if (cert.purposes === undefined)
+			cert.purposes = [];
+		var ekEnd = der.offset + der.length;
+		while (der.offset < ekEnd) {
+			var oid = der.readOID();
+			cert.purposes.push(EXTPURPOSE_REV[oid] || oid);
+		}
+		/*
+		 * This is a bit of a hack: in the case where we have a cert
+		 * that's only allowed to do serverAuth or clientAuth (and not
+		 * the other), we want to make sure all our Subjects are of
+		 * the right type. But we already parsed our Subjects and
+		 * decided if they were hosts or users earlier (since it appears
+		 * first in the cert).
+		 *
+		 * So we go through and mutate them into the right kind here if
+		 * it doesn't match. This might not be hugely beneficial, as it
+		 * seems that single-purpose certs are not often seen in the
+		 * wild.
+		 */
+		if (cert.purposes.indexOf('serverAuth') !== -1 &&
+		    cert.purposes.indexOf('clientAuth') === -1) {
+			cert.subjects.forEach(function (ide) {
+				if (ide.type !== 'host') {
+					ide.type = 'host';
+					ide.hostname = ide.uid ||
+					    ide.email ||
+					    ide.components[0].value;
+				}
+			});
+		} else if (cert.purposes.indexOf('clientAuth') !== -1 &&
+		    cert.purposes.indexOf('serverAuth') === -1) {
+			cert.subjects.forEach(function (ide) {
+				if (ide.type !== 'user') {
+					ide.type = 'user';
+					ide.uid = ide.hostname ||
+					    ide.email ||
+					    ide.components[0].value;
+				}
+			});
+		}
+		sig.extras.exts.push({ oid: extId, critical: critical });
+		break;
+	case (EXTS.keyUsage):
+		der.readSequence(asn1.Ber.OctetString);
+		var bits = der.readString(asn1.Ber.BitString, true);
+		var setBits = readBitField(bits, KEYUSEBITS);
+		setBits.forEach(function (bit) {
+			if (cert.purposes === undefined)
+				cert.purposes = [];
+			if (cert.purposes.indexOf(bit) === -1)
+				cert.purposes.push(bit);
+		});
+		sig.extras.exts.push({ oid: extId, critical: critical,
+		    bits: bits });
+		break;
+	case (EXTS.altName):
+		der.readSequence(asn1.Ber.OctetString);
+		der.readSequence();
+		var aeEnd = der.offset + der.length;
+		while (der.offset < aeEnd) {
+			switch (der.peek()) {
+			case ALTNAME.OtherName:
+			case ALTNAME.EDIPartyName:
+				der.readSequence();
+				der._offset += der.length;
+				break;
+			case ALTNAME.OID:
+				der.readOID(ALTNAME.OID);
+				break;
+			case ALTNAME.RFC822Name:
+				/* RFC822 specifies email addresses */
+				var email = der.readString(ALTNAME.RFC822Name);
+				id = Identity.forEmail(email);
+				if (!cert.subjects[0].equals(id))
+					cert.subjects.push(id);
+				break;
+			case ALTNAME.DirectoryName:
+				der.readSequence(ALTNAME.DirectoryName);
+				id = Identity.parseAsn1(der);
+				if (!cert.subjects[0].equals(id))
+					cert.subjects.push(id);
+				break;
+			case ALTNAME.DNSName:
+				var host = der.readString(
+				    ALTNAME.DNSName);
+				id = Identity.forHost(host);
+				if (!cert.subjects[0].equals(id))
+					cert.subjects.push(id);
+				break;
+			default:
+				der.readString(der.peek());
+				break;
+			}
+		}
+		sig.extras.exts.push({ oid: extId, critical: critical });
+		break;
+	default:
+		sig.extras.exts.push({
+			oid: extId,
+			critical: critical,
+			data: der.readString(asn1.Ber.OctetString, true)
+		});
+		break;
+	}
+
+	der._offset = after;
+}
+
+var UTCTIME_RE =
+    /^([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})?Z$/;
+function utcTimeToDate(t) {
+	var m = t.match(UTCTIME_RE);
+	assert.ok(m, 'timestamps must be in UTC');
+	var d = new Date();
+
+	var thisYear = d.getUTCFullYear();
+	var century = Math.floor(thisYear / 100) * 100;
+
+	var year = parseInt(m[1], 10);
+	if (thisYear % 100 < 50 && year >= 60)
+		year += (century - 1);
+	else
+		year += century;
+	d.setUTCFullYear(year, parseInt(m[2], 10) - 1, parseInt(m[3], 10));
+	d.setUTCHours(parseInt(m[4], 10), parseInt(m[5], 10));
+	if (m[6] && m[6].length > 0)
+		d.setUTCSeconds(parseInt(m[6], 10));
+	return (d);
+}
+
+var GTIME_RE =
+    /^([0-9]{4})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})?Z$/;
+function gTimeToDate(t) {
+	var m = t.match(GTIME_RE);
+	assert.ok(m);
+	var d = new Date();
+
+	d.setUTCFullYear(parseInt(m[1], 10), parseInt(m[2], 10) - 1,
+	    parseInt(m[3], 10));
+	d.setUTCHours(parseInt(m[4], 10), parseInt(m[5], 10));
+	if (m[6] && m[6].length > 0)
+		d.setUTCSeconds(parseInt(m[6], 10));
+	return (d);
+}
+
+function zeroPad(n, m) {
+	if (m === undefined)
+		m = 2;
+	var s = '' + n;
+	while (s.length < m)
+		s = '0' + s;
+	return (s);
+}
+
+function dateToUTCTime(d) {
+	var s = '';
+	s += zeroPad(d.getUTCFullYear() % 100);
+	s += zeroPad(d.getUTCMonth() + 1);
+	s += zeroPad(d.getUTCDate());
+	s += zeroPad(d.getUTCHours());
+	s += zeroPad(d.getUTCMinutes());
+	s += zeroPad(d.getUTCSeconds());
+	s += 'Z';
+	return (s);
+}
+
+function dateToGTime(d) {
+	var s = '';
+	s += zeroPad(d.getUTCFullYear(), 4);
+	s += zeroPad(d.getUTCMonth() + 1);
+	s += zeroPad(d.getUTCDate());
+	s += zeroPad(d.getUTCHours());
+	s += zeroPad(d.getUTCMinutes());
+	s += zeroPad(d.getUTCSeconds());
+	s += 'Z';
+	return (s);
+}
+
+function sign(cert, key) {
+	if (cert.signatures.x509 === undefined)
+		cert.signatures.x509 = {};
+	var sig = cert.signatures.x509;
+
+	sig.algo = key.type + '-' + key.defaultHashAlgorithm();
+	if (SIGN_ALGS[sig.algo] === undefined)
+		return (false);
+
+	var der = new asn1.BerWriter();
+	writeTBSCert(cert, der);
+	var blob = der.buffer;
+	sig.cache = blob;
+
+	var signer = key.createSign();
+	signer.write(blob);
+	cert.signatures.x509.signature = signer.sign();
+
+	return (true);
+}
+
+function signAsync(cert, signer, done) {
+	if (cert.signatures.x509 === undefined)
+		cert.signatures.x509 = {};
+	var sig = cert.signatures.x509;
+
+	var der = new asn1.BerWriter();
+	writeTBSCert(cert, der);
+	var blob = der.buffer;
+	sig.cache = blob;
+
+	signer(blob, function (err, signature) {
+		if (err) {
+			done(err);
+			return;
+		}
+		sig.algo = signature.type + '-' + signature.hashAlgorithm;
+		if (SIGN_ALGS[sig.algo] === undefined) {
+			done(new Error('Invalid signing algorithm "' +
+			    sig.algo + '"'));
+			return;
+		}
+		sig.signature = signature;
+		done();
+	});
+}
+
+function write(cert, options) {
+	var sig = cert.signatures.x509;
+	assert.object(sig, 'x509 signature');
+
+	var der = new asn1.BerWriter();
+	der.startSequence();
+	if (sig.cache) {
+		der._ensure(sig.cache.length);
+		sig.cache.copy(der._buf, der._offset);
+		der._offset += sig.cache.length;
+	} else {
+		writeTBSCert(cert, der);
+	}
+
+	der.startSequence();
+	der.writeOID(SIGN_ALGS[sig.algo]);
+	if (sig.algo.match(/^rsa-/))
+		der.writeNull();
+	der.endSequence();
+
+	var sigData = sig.signature.toBuffer('asn1');
+	var data = Buffer.alloc(sigData.length + 1);
+	data[0] = 0;
+	sigData.copy(data, 1);
+	der.writeBuffer(data, asn1.Ber.BitString);
+	der.endSequence();
+
+	return (der.buffer);
+}
+
+function writeTBSCert(cert, der) {
+	var sig = cert.signatures.x509;
+	assert.object(sig, 'x509 signature');
+
+	der.startSequence();
+
+	der.startSequence(Local(0));
+	der.writeInt(2);
+	der.endSequence();
+
+	der.writeBuffer(utils.mpNormalize(cert.serial), asn1.Ber.Integer);
+
+	der.startSequence();
+	der.writeOID(SIGN_ALGS[sig.algo]);
+	if (sig.algo.match(/^rsa-/))
+		der.writeNull();
+	der.endSequence();
+
+	cert.issuer.toAsn1(der);
+
+	der.startSequence();
+	writeDate(der, cert.validFrom);
+	writeDate(der, cert.validUntil);
+	der.endSequence();
+
+	var subject = cert.subjects[0];
+	var altNames = cert.subjects.slice(1);
+	subject.toAsn1(der);
+
+	pkcs8.writePkcs8(der, cert.subjectKey);
+
+	if (sig.extras && sig.extras.issuerUniqueID) {
+		der.writeBuffer(sig.extras.issuerUniqueID, Local(1));
+	}
+
+	if (sig.extras && sig.extras.subjectUniqueID) {
+		der.writeBuffer(sig.extras.subjectUniqueID, Local(2));
+	}
+
+	if (altNames.length > 0 || subject.type === 'host' ||
+	    (cert.purposes !== undefined && cert.purposes.length > 0) ||
+	    (sig.extras && sig.extras.exts)) {
+		der.startSequence(Local(3));
+		der.startSequence();
+
+		var exts = [];
+		if (cert.purposes !== undefined && cert.purposes.length > 0) {
+			exts.push({
+				oid: EXTS.basicConstraints,
+				critical: true
+			});
+			exts.push({
+				oid: EXTS.keyUsage,
+				critical: true
+			});
+			exts.push({
+				oid: EXTS.extKeyUsage,
+				critical: true
+			});
+		}
+		exts.push({ oid: EXTS.altName });
+		if (sig.extras && sig.extras.exts)
+			exts = sig.extras.exts;
+
+		for (var i = 0; i < exts.length; ++i) {
+			der.startSequence();
+			der.writeOID(exts[i].oid);
+
+			if (exts[i].critical !== undefined)
+				der.writeBoolean(exts[i].critical);
+
+			if (exts[i].oid === EXTS.altName) {
+				der.startSequence(asn1.Ber.OctetString);
+				der.startSequence();
+				if (subject.type === 'host') {
+					der.writeString(subject.hostname,
+					    Context(2));
+				}
+				for (var j = 0; j < altNames.length; ++j) {
+					if (altNames[j].type === 'host') {
+						der.writeString(
+						    altNames[j].hostname,
+						    ALTNAME.DNSName);
+					} else if (altNames[j].type ===
+					    'email') {
+						der.writeString(
+						    altNames[j].email,
+						    ALTNAME.RFC822Name);
+					} else {
+						/*
+						 * Encode anything else as a
+						 * DN style name for now.
+						 */
+						der.startSequence(
+						    ALTNAME.DirectoryName);
+						altNames[j].toAsn1(der);
+						der.endSequence();
+					}
+				}
+				der.endSequence();
+				der.endSequence();
+			} else if (exts[i].oid === EXTS.basicConstraints) {
+				der.startSequence(asn1.Ber.OctetString);
+				der.startSequence();
+				var ca = (cert.purposes.indexOf('ca') !== -1);
+				var pathLen = exts[i].pathLen;
+				der.writeBoolean(ca);
+				if (pathLen !== undefined)
+					der.writeInt(pathLen);
+				der.endSequence();
+				der.endSequence();
+			} else if (exts[i].oid === EXTS.extKeyUsage) {
+				der.startSequence(asn1.Ber.OctetString);
+				der.startSequence();
+				cert.purposes.forEach(function (purpose) {
+					if (purpose === 'ca')
+						return;
+					if (KEYUSEBITS.indexOf(purpose) !== -1)
+						return;
+					var oid = purpose;
+					if (EXTPURPOSE[purpose] !== undefined)
+						oid = EXTPURPOSE[purpose];
+					der.writeOID(oid);
+				});
+				der.endSequence();
+				der.endSequence();
+			} else if (exts[i].oid === EXTS.keyUsage) {
+				der.startSequence(asn1.Ber.OctetString);
+				/*
+				 * If we parsed this certificate from a byte
+				 * stream (i.e. we didn't generate it in sshpk)
+				 * then we'll have a ".bits" property on the
+				 * ext with the original raw byte contents.
+				 *
+				 * If we have this, use it here instead of
+				 * regenerating it. This guarantees we output
+				 * the same data we parsed, so signatures still
+				 * validate.
+				 */
+				if (exts[i].bits !== undefined) {
+					der.writeBuffer(exts[i].bits,
+					    asn1.Ber.BitString);
+				} else {
+					var bits = writeBitField(cert.purposes,
+					    KEYUSEBITS);
+					der.writeBuffer(bits,
+					    asn1.Ber.BitString);
+				}
+				der.endSequence();
+			} else {
+				der.writeBuffer(exts[i].data,
+				    asn1.Ber.OctetString);
+			}
+
+			der.endSequence();
+		}
+
+		der.endSequence();
+		der.endSequence();
+	}
+
+	der.endSequence();
+}
+
+/*
+ * Reads an ASN.1 BER bitfield out of the Buffer produced by doing
+ * `BerReader#readString(asn1.Ber.BitString)`. That function gives us the raw
+ * contents of the BitString tag, which is a count of unused bits followed by
+ * the bits as a right-padded byte string.
+ *
+ * `bits` is the Buffer, `bitIndex` should contain an array of string names
+ * for the bits in the string, ordered starting with bit #0 in the ASN.1 spec.
+ *
+ * Returns an array of Strings, the names of the bits that were set to 1.
+ */
+function readBitField(bits, bitIndex) {
+	var bitLen = 8 * (bits.length - 1) - bits[0];
+	var setBits = {};
+	for (var i = 0; i < bitLen; ++i) {
+		var byteN = 1 + Math.floor(i / 8);
+		var bit = 7 - (i % 8);
+		var mask = 1 << bit;
+		var bitVal = ((bits[byteN] & mask) !== 0);
+		var name = bitIndex[i];
+		if (bitVal && typeof (name) === 'string') {
+			setBits[name] = true;
+		}
+	}
+	return (Object.keys(setBits));
+}
+
+/*
+ * `setBits` is an array of strings, containing the names for each bit that
+ * sould be set to 1. `bitIndex` is same as in `readBitField()`.
+ *
+ * Returns a Buffer, ready to be written out with `BerWriter#writeString()`.
+ */
+function writeBitField(setBits, bitIndex) {
+	var bitLen = bitIndex.length;
+	var blen = Math.ceil(bitLen / 8);
+	var unused = blen * 8 - bitLen;
+	var bits = Buffer.alloc(1 + blen); // zero-filled
+	bits[0] = unused;
+	for (var i = 0; i < bitLen; ++i) {
+		var byteN = 1 + Math.floor(i / 8);
+		var bit = 7 - (i % 8);
+		var mask = 1 << bit;
+		var name = bitIndex[i];
+		if (name === undefined)
+			continue;
+		var bitVal = (setBits.indexOf(name) !== -1);
+		if (bitVal) {
+			bits[byteN] |= mask;
+		}
+	}
+	return (bits);
+}