一、

下午在編寫ECDH演算法中乙方用甲方公鑰產生金鑰時，想到keyFactory能把金鑰材料變成金鑰，我是這麼敲的：

	public static final Map<String,Object> initKey(byte[] key) throws NoSuchAlgorithmException, InvalidKeySpecException{
		X509EncodedKeySpec x509EncodedKeySpec = new X509EncodedKeySpec(key);
		
		KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
		ECPublicKey pubKey = (ECPublicKey)keyFactory.generatePublic(x509EncodedKeySpec);
		
		ECParameterSpec ecParam = pubKey.getParams();
		
		ECPublicKey publicKey = (ECPublicKey) keyFactory.generatePublic((KeySpec) ecParam);
		ECPrivateKey privateKey = (ECPrivateKey)keyFactory.generatePrivate((KeySpec)ecParam);
		
		Map<String,Object> keyMap = new HashMap<String,Object>(2);
		keyMap.put(PUBLIC_KEY, publicKey);
		keyMap.put(PRIVATE_KEY, privateKey);
		
		return keyMap;
		
	}
 

Junit報錯：java.lang.ClassCastException: sun.security.ec.NamedCurve cannot be cast to java.security.spec.KeySpec
at com.fdc.ECDHCoder.initKey(ECDHCoder.java:63)
at com.fdc.ECDHCoderTest.initKey(ECDHCoderTest.java:36)
……

通過查證發現，ECParameterSpec物件並非KeySpec的子類，它們的關係是這樣的：

interface	AlgorithmParamSpec
class	ECParamterSpec

ECParamterSpec實現了AlgorithmParamSpec介面

而KeyPairGenerator能接收這個引數

Class KeyPairGenerator

void	Initializes the key pair generator using the specified parameter set and the SecureRandomimplementation of the highest-priority installed provider as the source of randomness.
void	Initializes the key pair generator with the given parameter set and source of randomness.
void	Initializes the key pair generator for a certain keysize using a default parameter set and theSecureRandom implementation of the highest-priority installed provider as the source of randomness.
void	Initializes the key pair generator for a certain keysize with the given source of randomness (and a default parameter set).

進一步查詢得到：

Interface KeySpec

Class KeyFactory

• • java.security.KeyFactory

Modifier and Type	Method and Description
Generates a private key object from the provided key specification (key material).

而且並沒有產生SecretKey的方法，回到AES演算法發現，原來當時的secretKey是由SecretKeyFactory產生的

Class SecretKeyFactory

• • javax.crypto.SecretKeyFactory

Modifier and Type	Method and Description
Generates a SecretKey object from the provided key specification (key material).

不但如此，SecretKeyFactory並不繼承KeyFactory，兩者是並列的！

綜上，

KeyFactory的作用細化為：可將金鑰材料類KeySpec物件轉換成PublicKey,PrivateKey類物件

Interface PublicKey

二、BouncyCastle安裝

http://www.bouncycastle.org/latest_releases.html

注意JDK,JRE目錄下java,security的替換

三、小結：

1.DH演算法的精髓：甲乙雙方並沒有交換本地金鑰，依然可以完成資料對稱加密的實現！

2.ECDH演算法金鑰長度取值：112,256,571，對本地金鑰的演算法不如DH那樣全面，AES,DES,DESede都失敗

3.X509EncodedKeySpec 和 PKCS8KeySpec 為EncodedKeySpec的子類，前者用於轉換公鑰編碼金鑰，後者用於轉換私鑰編碼金鑰