bitaddress.org/src/ninja.key.js

var ninja = { wallets: {} };

ninja.privateKey = {
	isPrivateKey: function (key) {
		return (
					Bitcoin.ECKey.isWalletImportFormat(key) ||
					Bitcoin.ECKey.isCompressedWalletImportFormat(key) ||
					Bitcoin.ECKey.isHexFormat(key) ||
					Bitcoin.ECKey.isBase64Format(key) ||
					Bitcoin.ECKey.isMiniFormat(key)
				);
	},
	getECKeyFromAdding: function (privKey1, privKey2) {
		var n = EllipticCurve.getSECCurveByName("secp256k1").getN();
		var ecKey1 = new Bitcoin.ECKey(privKey1);
		var ecKey2 = new Bitcoin.ECKey(privKey2);
		// if both keys are the same return null
		if (ecKey1.getBitcoinHexFormat() == ecKey2.getBitcoinHexFormat()) return null;
		if (ecKey1 == null || ecKey2 == null) return null;
		var combinedPrivateKey = new Bitcoin.ECKey(ecKey1.priv.add(ecKey2.priv).mod(n));
		// compressed when both keys are compressed
		if (ecKey1.compressed && ecKey2.compressed) combinedPrivateKey.setCompressed(true);
		return combinedPrivateKey;
	},
	getECKeyFromMultiplying: function (privKey1, privKey2) {
		var n = EllipticCurve.getSECCurveByName("secp256k1").getN();
		var ecKey1 = new Bitcoin.ECKey(privKey1);
		var ecKey2 = new Bitcoin.ECKey(privKey2);
		// if both keys are the same return null
		if (ecKey1.getBitcoinHexFormat() == ecKey2.getBitcoinHexFormat()) return null;
		if (ecKey1 == null || ecKey2 == null) return null;
		var combinedPrivateKey = new Bitcoin.ECKey(ecKey1.priv.multiply(ecKey2.priv).mod(n));
		// compressed when both keys are compressed
		if (ecKey1.compressed && ecKey2.compressed) combinedPrivateKey.setCompressed(true);
		return combinedPrivateKey;
	},
	// 58 base58 characters starting with 6P
	isBIP38Format: function (key) {
		return (/^6P[123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz]{56}$/.test(key));
	},
	BIP38EncryptedKeyToByteArrayAsync: function (base58Encrypted, passphrase, callback) {
		var hex;
		try {
			hex = Bitcoin.Base58.decode(base58Encrypted);
		} catch (e) {
			callback(new Error(ninja.translator.get("detailalertnotvalidprivatekey")));
			return;
		}

		// 43 bytes: 2 bytes prefix, 37 bytes payload, 4 bytes checksum
		if (hex.length != 43) {
			callback(new Error(ninja.translator.get("detailalertnotvalidprivatekey")));
			return;
		}
		// first byte is always 0x01 
		else if (hex[0] != 0x01) {
			callback(new Error(ninja.translator.get("detailalertnotvalidprivatekey")));
			return;
		}

		var expChecksum = hex.slice(-4);
		hex = hex.slice(0, -4);
		var checksum = Bitcoin.Util.dsha256(hex);
		if (checksum[0] != expChecksum[0] || checksum[1] != expChecksum[1] || checksum[2] != expChecksum[2] || checksum[3] != expChecksum[3]) {
			callback(new Error(ninja.translator.get("detailalertnotvalidprivatekey")));
			return;
		}

		var isCompPoint = false;
		var isECMult = false;
		var hasLotSeq = false;
		// second byte for non-EC-multiplied key
		if (hex[1] == 0x42) {
			// key should use compression
			if (hex[2] == 0xe0) {
				isCompPoint = true;
			}
			// key should NOT use compression
			else if (hex[2] != 0xc0) {
				callback(new Error(ninja.translator.get("detailalertnotvalidprivatekey")));
				return;
			}
		}
		// second byte for EC-multiplied key 
		else if (hex[1] == 0x43) {
			isECMult = true;
			isCompPoint = (hex[2] & 0x20) != 0;
			hasLotSeq = (hex[2] & 0x04) != 0;
			if ((hex[2] & 0x24) != hex[2]) {
				callback(new Error(ninja.translator.get("detailalertnotvalidprivatekey")));
				return;
			}
		}
		else {
			callback(new Error(ninja.translator.get("detailalertnotvalidprivatekey")));
			return;
		}

		var decrypted;
		var AES_opts = { mode: new Crypto.mode.ECB(Crypto.pad.NoPadding), asBytes: true };

		var verifyHashAndReturn = function () {
			var tmpkey = new Bitcoin.ECKey(decrypted); // decrypted using closure
			var base58AddrText = tmpkey.setCompressed(isCompPoint).getBitcoinAddress(); // isCompPoint using closure
			checksum = Bitcoin.Util.dsha256(base58AddrText); // checksum using closure

			if (checksum[0] != hex[3] || checksum[1] != hex[4] || checksum[2] != hex[5] || checksum[3] != hex[6]) {
				callback(new Error(ninja.translator.get("bip38alertincorrectpassphrase"))); // callback using closure
				return;
			}
			callback(tmpkey.getBitcoinPrivateKeyByteArray()); // callback using closure
		};

		if (!isECMult) {
			var addresshash = hex.slice(3, 7);
			Crypto_scrypt(passphrase, addresshash, 16384, 8, 8, 64, function (derivedBytes) {
				var k = derivedBytes.slice(32, 32 + 32);
				decrypted = Crypto.AES.decrypt(hex.slice(7, 7 + 32), k, AES_opts);
				for (var x = 0; x < 32; x++) decrypted[x] ^= derivedBytes[x];
				verifyHashAndReturn(); //TODO: pass in 'decrypted' as a param
			});
		}
		else {
			var ownerentropy = hex.slice(7, 7 + 8);
			var ownersalt = !hasLotSeq ? ownerentropy : ownerentropy.slice(0, 4);
			Crypto_scrypt(passphrase, ownersalt, 16384, 8, 8, 32, function (prefactorA) {
				var passfactor;
				if (!hasLotSeq) { // hasLotSeq using closure
					passfactor = prefactorA;
				} else {
					var prefactorB = prefactorA.concat(ownerentropy); // ownerentropy using closure
					passfactor = Bitcoin.Util.dsha256(prefactorB);
				}
				var kp = new Bitcoin.ECKey(passfactor);
				var passpoint = kp.setCompressed(true).getPub();

				var encryptedpart2 = hex.slice(23, 23 + 16);

				var addresshashplusownerentropy = hex.slice(3, 3 + 12);
				Crypto_scrypt(passpoint, addresshashplusownerentropy, 1024, 1, 1, 64, function (derived) {
					var k = derived.slice(32);

					var unencryptedpart2 = Crypto.AES.decrypt(encryptedpart2, k, AES_opts);
					for (var i = 0; i < 16; i++) { unencryptedpart2[i] ^= derived[i + 16]; }

					var encryptedpart1 = hex.slice(15, 15 + 8).concat(unencryptedpart2.slice(0, 0 + 8));
					var unencryptedpart1 = Crypto.AES.decrypt(encryptedpart1, k, AES_opts);
					for (var i = 0; i < 16; i++) { unencryptedpart1[i] ^= derived[i]; }

					var seedb = unencryptedpart1.slice(0, 0 + 16).concat(unencryptedpart2.slice(8, 8 + 8));

					var factorb = Bitcoin.Util.dsha256(seedb);

					var ps = EllipticCurve.getSECCurveByName("secp256k1");
					var privateKey = BigInteger.fromByteArrayUnsigned(passfactor).multiply(BigInteger.fromByteArrayUnsigned(factorb)).remainder(ps.getN());

					decrypted = privateKey.toByteArrayUnsigned();
					verifyHashAndReturn();
				});
			});
		}
	}
};

ninja.publicKey = {
	isPublicKeyHexFormat: function (key) {
		key = key.toString();
		return ninja.publicKey.isUncompressedPublicKeyHexFormat(key) || ninja.publicKey.isCompressedPublicKeyHexFormat(key);
	},
	// 130 characters [0-9A-F] starts with 04
	isUncompressedPublicKeyHexFormat: function (key) {
		key = key.toString();
		return /^04[A-Fa-f0-9]{128}$/.test(key);
	},
	// 66 characters [0-9A-F] starts with 02 or 03
	isCompressedPublicKeyHexFormat: function (key) {
		key = key.toString();
		return /^0[2-3][A-Fa-f0-9]{64}$/.test(key);
	},
	getBitcoinAddressFromByteArray: function (pubKeyByteArray) {
		var pubKeyHash = Bitcoin.Util.sha256ripe160(pubKeyByteArray);
		var addr = new Bitcoin.Address(pubKeyHash);
		return addr.toString();
	},
	getHexFromByteArray: function (pubKeyByteArray) {
		return Crypto.util.bytesToHex(pubKeyByteArray).toString().toUpperCase();
	},
	getByteArrayFromAdding: function (pubKeyHex1, pubKeyHex2) {
		var ecparams = EllipticCurve.getSECCurveByName("secp256k1");
		var curve = ecparams.getCurve();
		var ecPoint1 = curve.decodePointHex(pubKeyHex1);
		var ecPoint2 = curve.decodePointHex(pubKeyHex2);
		// if both points are the same return null
		if (ecPoint1.equals(ecPoint2)) return null;
		var compressed = (ecPoint1.compressed && ecPoint2.compressed);
		var pubKey = ecPoint1.add(ecPoint2).getEncoded(compressed);
		return pubKey;
	},
	getByteArrayFromMultiplying: function (pubKeyHex, ecKey) {
		var ecparams = EllipticCurve.getSECCurveByName("secp256k1");
		var ecPoint = ecparams.getCurve().decodePointHex(pubKeyHex);
		var compressed = (ecPoint.compressed && ecKey.compressed);
		// if both points are the same return null
		ecKey.setCompressed(false);
		if (ecPoint.equals(ecKey.getPubPoint())) {
			return null;
		}
		var bigInt = ecKey.priv;
		var pubKey = ecPoint.multiply(bigInt).getEncoded(compressed);
		return pubKey;
	},
	// used by unit test
	getDecompressedPubKeyHex: function (pubKeyHexComp) {
		var ecparams = EllipticCurve.getSECCurveByName("secp256k1");
		var ecPoint = ecparams.getCurve().decodePointHex(pubKeyHexComp);
		var pubByteArray = ecPoint.getEncoded(0);
		var pubHexUncompressed = ninja.publicKey.getHexFromByteArray(pubByteArray);
		return pubHexUncompressed;
	}
};