text: // Copyright 2015 Joyent, Inc.
  
  module.exports = {
  	bufferSplit: bufferSplit,
  	addRSAMissing: addRSAMissing,
  	calculateDSAPublic: calculateDSAPublic,
  	calculateED25519Public: calculateED25519Public,
  	calculateX25519Public: calculateX25519Public,
  	mpNormalize: mpNormalize,
  	mpDenormalize: mpDenormalize,
  	ecNormalize: ecNormalize,
  	countZeros: countZeros,
  	assertCompatible: assertCompatible,
  	isCompatible: isCompatible,
  	opensslKeyDeriv: opensslKeyDeriv,
  	opensshCipherInfo: opensshCipherInfo,
  	publicFromPrivateECDSA: publicFromPrivateECDSA,
  	zeroPadToLength: zeroPadToLength,
  	writeBitString: writeBitString,
  	readBitString: readBitString
  };
  
  var assert = require('assert-plus');
  var Buffer = require('safer-buffer').Buffer;
  var PrivateKey = require('./private-key');
  var Key = require('./key');
  var crypto = require('crypto');
  var algs = require('./algs');
  var asn1 = require('asn1');
  
  var ec, jsbn;
  var nacl;
  
  var MAX_CLASS_DEPTH = 3;
  
  function isCompatible(obj, klass, needVer) {
  	if (obj === null || typeof (obj) !== 'object')
  		return (false);
  	if (needVer === undefined)
  		needVer = klass.prototype._sshpkApiVersion;
  	if (obj instanceof klass &&
  	    klass.prototype._sshpkApiVersion[0] == needVer[0])
  		return (true);
  	var proto = Object.getPrototypeOf(obj);
  	var depth = 0;
  	while (proto.constructor.name !== klass.name) {
  		proto = Object.getPrototypeOf(proto);
  		if (!proto || ++depth > MAX_CLASS_DEPTH)
  			return (false);
  	}
  	if (proto.constructor.name !== klass.name)
  		return (false);
  	var ver = proto._sshpkApiVersion;
  	if (ver === undefined)
  		ver = klass._oldVersionDetect(obj);
  	if (ver[0] != needVer[0] || ver[1] < needVer[1])
  		return (false);
  	return (true);
  }
  
  function assertCompatible(obj, klass, needVer, name) {
  	if (name === undefined)
  		name = 'object';
  	assert.ok(obj, name + ' must not be null');
  	assert.object(obj, name + ' must be an object');
  	if (needVer === undefined)
  		needVer = klass.prototype._sshpkApiVersion;
  	if (obj instanceof klass &&
  	    klass.prototype._sshpkApiVersion[0] == needVer[0])
  		return;
  	var proto = Object.getPrototypeOf(obj);
  	var depth = 0;
  	while (proto.constructor.name !== klass.name) {
  		proto = Object.getPrototypeOf(proto);
  		assert.ok(proto && ++depth <= MAX_CLASS_DEPTH,
  		    name + ' must be a ' + klass.name + ' instance');
  	}
  	assert.strictEqual(proto.constructor.name, klass.name,
  	    name + ' must be a ' + klass.name + ' instance');
  	var ver = proto._sshpkApiVersion;
  	if (ver === undefined)
  		ver = klass._oldVersionDetect(obj);
  	assert.ok(ver[0] == needVer[0] && ver[1] >= needVer[1],
  	    name + ' must be compatible with ' + klass.name + ' klass ' +
  	    'version ' + needVer[0] + '.' + needVer[1]);
  }
  
  var CIPHER_LEN = {
  	'des-ede3-cbc': { key: 7, iv: 8 },
  	'aes-128-cbc': { key: 16, iv: 16 }
  };
  var PKCS5_SALT_LEN = 8;
  
  function opensslKeyDeriv(cipher, salt, passphrase, count) {
  	assert.buffer(salt, 'salt');
  	assert.buffer(passphrase, 'passphrase');
  	assert.number(count, 'iteration count');
  
  	var clen = CIPHER_LEN[cipher];
  	assert.object(clen, 'supported cipher');
  
  	salt = salt.slice(0, PKCS5_SALT_LEN);
  
  	var D, D_prev, bufs;
  	var material = Buffer.alloc(0);
  	while (material.length < clen.key + clen.iv) {
  		bufs = [];
  		if (D_prev)
  			bufs.push(D_prev);
  		bufs.push(passphrase);
  		bufs.push(salt);
  		D = Buffer.concat(bufs);
  		for (var j = 0; j < count; ++j)
  			D = crypto.createHash('md5').update(D).digest();
  		material = Buffer.concat([material, D]);
  		D_prev = D;
  	}
  
  	return ({
  	    key: material.slice(0, clen.key),
  	    iv: material.slice(clen.key, clen.key + clen.iv)
  	});
  }
  
  /* Count leading zero bits on a buffer */
  function countZeros(buf) {
  	var o = 0, obit = 8;
  	while (o < buf.length) {
  		var mask = (1 << obit);
  		if ((buf[o] & mask) === mask)
  			break;
  		obit--;
  		if (obit < 0) {
  			o++;
  			obit = 8;
  		}
  	}
  	return (o*8 + (8 - obit) - 1);
  }
  
  function bufferSplit(buf, chr) {
  	assert.buffer(buf);
  	assert.string(chr);
  
  	var parts = [];
  	var lastPart = 0;
  	var matches = 0;
  	for (var i = 0; i < buf.length; ++i) {
  		if (buf[i] === chr.charCodeAt(matches))
  			++matches;
  		else if (buf[i] === chr.charCodeAt(0))
  			matches = 1;
  		else
  			matches = 0;
  
  		if (matches >= chr.length) {
  			var newPart = i + 1;
  			parts.push(buf.slice(lastPart, newPart - matches));
  			lastPart = newPart;
  			matches = 0;
  		}
  	}
  	if (lastPart <= buf.length)
  		parts.push(buf.slice(lastPart, buf.length));
  
  	return (parts);
  }
  
  function ecNormalize(buf, addZero) {
  	assert.buffer(buf);
  	if (buf[0] === 0x00 && buf[1] === 0x04) {
  		if (addZero)
  			return (buf);
  		return (buf.slice(1));
  	} else if (buf[0] === 0x04) {
  		if (!addZero)
  			return (buf);
  	} else {
  		while (buf[0] === 0x00)
  			buf = buf.slice(1);
  		if (buf[0] === 0x02 || buf[0] === 0x03)
  			throw (new Error('Compressed elliptic curve points ' +
  			    'are not supported'));
  		if (buf[0] !== 0x04)
  			throw (new Error('Not a valid elliptic curve point'));
  		if (!addZero)
  			return (buf);
  	}
  	var b = Buffer.alloc(buf.length + 1);
  	b[0] = 0x0;
  	buf.copy(b, 1);
  	return (b);
  }
  
  function readBitString(der, tag) {
  	if (tag === undefined)
  		tag = asn1.Ber.BitString;
  	var buf = der.readString(tag, true);
  	assert.strictEqual(buf[0], 0x00, 'bit strings with unused bits are ' +
  	    'not supported (0x' + buf[0].toString(16) + ')');
  	return (buf.slice(1));
  }
  
  function writeBitString(der, buf, tag) {
  	if (tag === undefined)
  		tag = asn1.Ber.BitString;
  	var b = Buffer.alloc(buf.length + 1);
  	b[0] = 0x00;
  	buf.copy(b, 1);
  	der.writeBuffer(b, tag);
  }
  
  function mpNormalize(buf) {
  	assert.buffer(buf);
  	while (buf.length > 1 && buf[0] === 0x00 && (buf[1] & 0x80) === 0x00)
  		buf = buf.slice(1);
  	if ((buf[0] & 0x80) === 0x80) {
  		var b = Buffer.alloc(buf.length + 1);
  		b[0] = 0x00;
  		buf.copy(b, 1);
  		buf = b;
  	}
  	return (buf);
  }
  
  function mpDenormalize(buf) {
  	assert.buffer(buf);
  	while (buf.length > 1 && buf[0] === 0x00)
  		buf = buf.slice(1);
  	return (buf);
  }
  
  function zeroPadToLength(buf, len) {
  	assert.buffer(buf);
  	assert.number(len);
  	while (buf.length > len) {
  		assert.equal(buf[0], 0x00);
  		buf = buf.slice(1);
  	}
  	while (buf.length < len) {
  		var b = Buffer.alloc(buf.length + 1);
  		b[0] = 0x00;
  		buf.copy(b, 1);
  		buf = b;
  	}
  	return (buf);
  }
  
  function bigintToMpBuf(bigint) {
  	var buf = Buffer.from(bigint.toByteArray());
  	buf = mpNormalize(buf);
  	return (buf);
  }
  
  function calculateDSAPublic(g, p, x) {
  	assert.buffer(g);
  	assert.buffer(p);
  	assert.buffer(x);
  	try {
  		var bigInt = require('jsbn').BigInteger;
  	} catch (e) {
  		throw (new Error('To load a PKCS#8 format DSA private key, ' +
  		    'the node jsbn library is required.'));
  	}
  	g = new bigInt(g);
  	p = new bigInt(p);
  	x = new bigInt(x);
  	var y = g.modPow(x, p);
  	var ybuf = bigintToMpBuf(y);
  	return (ybuf);
  }
  
  function calculateED25519Public(k) {
  	assert.buffer(k);
  
  	if (nacl === undefined)
  		nacl = require('tweetnacl');
  
  	var kp = nacl.sign.keyPair.fromSeed(new Uint8Array(k));
  	return (Buffer.from(kp.publicKey));
  }
  
  function calculateX25519Public(k) {
  	assert.buffer(k);
  
  	if (nacl === undefined)
  		nacl = require('tweetnacl');
  
  	var kp = nacl.box.keyPair.fromSeed(new Uint8Array(k));
  	return (Buffer.from(kp.publicKey));
  }
  
  function addRSAMissing(key) {
  	assert.object(key);
  	assertCompatible(key, PrivateKey, [1, 1]);
  	try {
  		var bigInt = require('jsbn').BigInteger;
  	} catch (e) {
  		throw (new Error('To write a PEM private key from ' +
  		    'this source, the node jsbn lib is required.'));
  	}
  
  	var d = new bigInt(key.part.d.data);
  	var buf;
  
  	if (!key.part.dmodp) {
  		var p = new bigInt(key.part.p.data);
  		var dmodp = d.mod(p.subtract(1));
  
  		buf = bigintToMpBuf(dmodp);
  		key.part.dmodp = {name: 'dmodp', data: buf};
  		key.parts.push(key.part.dmodp);
  	}
  	if (!key.part.dmodq) {
  		var q = new bigInt(key.part.q.data);
  		var dmodq = d.mod(q.subtract(1));
  
  		buf = bigintToMpBuf(dmodq);
  		key.part.dmodq = {name: 'dmodq', data: buf};
  		key.parts.push(key.part.dmodq);
  	}
  }
  
  function publicFromPrivateECDSA(curveName, priv) {
  	assert.string(curveName, 'curveName');
  	assert.buffer(priv);
  	if (ec === undefined)
  		ec = require('ecc-jsbn/lib/ec');
  	if (jsbn === undefined)
  		jsbn = require('jsbn').BigInteger;
  	var params = algs.curves[curveName];
  	var p = new jsbn(params.p);
  	var a = new jsbn(params.a);
  	var b = new jsbn(params.b);
  	var curve = new ec.ECCurveFp(p, a, b);
  	var G = curve.decodePointHex(params.G.toString('hex'));
  
  	var d = new jsbn(mpNormalize(priv));
  	var pub = G.multiply(d);
  	pub = Buffer.from(curve.encodePointHex(pub), 'hex');
  
  	var parts = [];
  	parts.push({name: 'curve', data: Buffer.from(curveName)});
  	parts.push({name: 'Q', data: pub});
  
  	var key = new Key({type: 'ecdsa', curve: curve, parts: parts});
  	return (key);
  }
  
  function opensshCipherInfo(cipher) {
  	var inf = {};
  	switch (cipher) {
  	case '3des-cbc':
  		inf.keySize = 24;
  		inf.blockSize = 8;
  		inf.opensslName = 'des-ede3-cbc';
  		break;
  	case 'blowfish-cbc':
  		inf.keySize = 16;
  		inf.blockSize = 8;
  		inf.opensslName = 'bf-cbc';
  		break;
  	case 'aes128-cbc':
  	case 'aes128-ctr':
  	case 'aes128-gcm@openssh.com':
  		inf.keySize = 16;
  		inf.blockSize = 16;
  		inf.opensslName = 'aes-128-' + cipher.slice(7, 10);
  		break;
  	case 'aes192-cbc':
  	case 'aes192-ctr':
  	case 'aes192-gcm@openssh.com':
  		inf.keySize = 24;
  		inf.blockSize = 16;
  		inf.opensslName = 'aes-192-' + cipher.slice(7, 10);
  		break;
  	case 'aes256-cbc':
  	case 'aes256-ctr':
  	case 'aes256-gcm@openssh.com':
  		inf.keySize = 32;
  		inf.blockSize = 16;
  		inf.opensslName = 'aes-256-' + cipher.slice(7, 10);
  		break;
  	default:
  		throw (new Error(
  		    'Unsupported openssl cipher "' + cipher + '"'));
  	}
  	return (inf);
  }
  