要实现加解密,最简单实现如下：
核心类Ciper,三步走：（以"RSA"为例）
1.获取Keypair（公钥私钥对）。生成或者获取公钥和私钥。
生成Keypair过程，可以写死到文件里，去读取。或者通过api自动生成。
2.实例化Cipher，约定算法
2.初始化Cipher，定义是加密还是解密。是公约加密啊，还是私钥加密，是公钥解密，还是私钥解密。
3.获取加密或解密的结果。
// KeyPairGenerator类用于生成公钥和私钥对，基于RSA算法生成对象
KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
// 初始化密钥对生成器，密钥大小为96-1024位
keyPairGen.initialize(1024,new SecureRandom());
// 生成一个密钥对，保存在keyPair中
KeyPair keyPair = keyPairGen.generateKeyPair();
RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate(); // 得到私钥
RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic(); // 得到公钥
//**公钥加密**
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher. ENCRYPT_MODE, publicKey);
cipher.doFinal(minwen.getBytes("UTF-8")
//**私钥解密**
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
cipher.doFinal(miwen.getBytes("UTF-8")
补充：
a) 由于多平台加解密会存在不兼容的问题。（如：Android系统和windows，linux平台默认支持的加密算法不一致）Ciper实例化，需要使用第三方类 BouncyCastleProvider 代码如下：
Cipher cipher = Cipher.getInstance("RSA/NONE/PKCS1Padding",
new BouncyCastleProvider().getName());
//算法类型/工作方式/填充方式
b) 为了让字节数组转字符串格式固定，一般需要用到base64转码
apache.commons-codex下的base64类
//base64 解码
public static String decode(byte[] bytes) {
return new String(Base64.decodeBase64(bytes));
}
//base64 编码
public static String encode(byte[] bytes) {
return new String(Base64.encodeBase64(bytes));
}
c) 如果要打印出公钥，私钥，可通过 java.security.Key获取字节，再转字符串。
/**
* Returns the key in its primary encoding format, or null
* if this key does not support encoding.
*
* @return the encoded key, or null if the key does not support
* encoding.
*/
public byte[] getEncoded();
d) 若有需要在加解密中加入自己的算法逻辑，如字节数组重排等，可见Ciper类其他api。
/**
* Finishes a multi-part transformation (encryption or decryption).
* <p>
* Processes any bytes that may have been buffered in previous {@code
* update} calls.
* <p>
* The final transformed bytes are stored in the {@code output} buffer.
*
* @param output
* the output buffer.
* @param outputOffset
* the offset in the output buffer.
* @return the number of bytes placed in the output buffer.
* @throws IllegalBlockSizeException
* if the size of the resulting bytes is not a multiple of the
* cipher block size.
* @throws ShortBufferException
* if the size of the {@code output} buffer is too small.
* @throws BadPaddingException
* if the padding of the data does not match the padding scheme.
* @throws IllegalStateException
* if this cipher instance is not initialized for encryption or
* decryption.
*/
public final int doFinal(byte[] output, int outputOffset)
throws IllegalBlockSizeException, ShortBufferException,
BadPaddingException {
if (mode != ENCRYPT_MODE && mode != DECRYPT_MODE) {
throw new IllegalStateException();
}
if (outputOffset < 0) {
throw new IllegalArgumentException("outputOffset < 0. outputOffset=" + outputOffset);
}
return getSpi().engineDoFinal(null, 0, 0, output, outputOffset);
}
/**
* Finishes a multi-part transformation (encryption or decryption).
* <p>
* Processes the bytes in {@code input} buffer, and any bytes that have been
* buffered in previous {@code update} calls.
*
* @param input
* the input buffer.
* @return the final bytes from the transformation.
* @throws IllegalBlockSizeException
* if the size of the resulting bytes is not a multiple of the
* cipher block size.
* @throws BadPaddingException
* if the padding of the data does not match the padding scheme.
* @throws IllegalStateException
* if this cipher instance is not initialized for encryption or
* decryption.
*/
public final byte[] doFinal(byte[] input) throws IllegalBlockSizeException,
BadPaddingException {
if (mode != ENCRYPT_MODE && mode != DECRYPT_MODE) {
throw new IllegalStateException();
}
return getSpi().engineDoFinal(input, 0, input.length);
}
/**
* Finishes a multi-part transformation (encryption or decryption).
* <p>
* Processes the {@code inputLen} bytes in {@code input} buffer at {@code
* inputOffset}, and any bytes that have been buffered in previous {@code
* update} calls.
*
* @param input
* the input buffer.
* @param inputOffset
* the offset in the input buffer.
* @param inputLen
* the length of the input
* @return the final bytes from the transformation.
* @throws IllegalBlockSizeException
* if the size of the resulting bytes is not a multiple of the
* cipher block size.
* @throws BadPaddingException
* if the padding of the data does not match the padding scheme.
* @throws IllegalStateException
* if this cipher instance is not initialized for encryption or
* decryption.
* @throws IllegalArgumentException
* if {@code inputOffset} and {@code inputLen} do not specify an
* valid chunk in the input buffer.
*/
public final byte[] doFinal(byte[] input, int inputOffset, int inputLen)
throws IllegalBlockSizeException, BadPaddingException {
if (mode != ENCRYPT_MODE && mode != DECRYPT_MODE) {
throw new IllegalStateException();
}
checkInputOffsetAndCount(input.length, inputOffset, inputLen);
return getSpi().engineDoFinal(input, inputOffset, inputLen);
}
/**
* Finishes a multi-part transformation (encryption or decryption).
* <p>
* Processes the {@code inputLen} bytes in {@code input} buffer at {@code
* inputOffset}, and any bytes that have been buffered in previous {@code
* update} calls.
*
* @param input
* the input buffer.
* @param inputOffset
* the offset in the input buffer.
* @param inputLen
* the length of the input.
* @param output
* the output buffer for the transformed bytes.
* @param outputOffset
* the offset in the output buffer.
* @return the number of bytes placed in the output buffer.
* @throws ShortBufferException
* if the size of the {@code output} buffer is too small.
* @throws IllegalBlockSizeException
* if the size of the resulting bytes is not a multiple of the
* cipher block size.
* @throws BadPaddingException
* if the padding of the data does not match the padding scheme.
* @throws IllegalStateException
* if this cipher instance is not initialized for encryption or
* decryption.
* @throws IllegalArgumentException
* if {@code inputOffset} and {@code inputLen} do not specify an
* valid chunk in the input buffer.
*/
public final int doFinal(byte[] input, int inputOffset, int inputLen,
byte[] output, int outputOffset) throws ShortBufferException,
IllegalBlockSizeException, BadPaddingException {
if (mode != ENCRYPT_MODE && mode != DECRYPT_MODE) {
throw new IllegalStateException();
}
checkInputOffsetAndCount(input.length, inputOffset, inputLen);
return getSpi().engineDoFinal(input, inputOffset, inputLen, output,
outputOffset);
}
/**
* Continues a multi-part transformation (encryption or decryption). The
* transformed bytes are returned.
*
* @param input
* the input bytes to transform.
* @return the transformed bytes in a new buffer, or {@code null} if the
* input has zero length.
* @throws IllegalStateException
* if this cipher instance is not initialized for encryption or
* decryption.
* @throws IllegalArgumentException
* if the input is {@code null}.
*/
public final byte[] update(byte[] input) {
if (mode != ENCRYPT_MODE && mode != DECRYPT_MODE) {
throw new IllegalStateException();
}
if (input == null) {
throw new IllegalArgumentException("input == null");
}
if (input.length == 0) {
return null;
}
return getSpi().engineUpdate(input, 0, input.length);
}
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