對接場景：

伺服器端使用java生成公鑰和私鑰，將公鑰傳遞給iOS加密 or 將私鑰傳遞給iOS端使用openssl進行簽名，然後在伺服器端進行驗證

java端：

1、使用常規的KeyPairGenerator類生成公鑰和私鑰

KeyPairGenerator gen = KeyPairGenerator.getInstance(RSA);
gen.initialize(1024, new SecureRandom());
KeyPair keyPair = gen.generateKeyPair();
RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();	
RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate(); 
 

2、常規生成的私鑰格式是DER的，而iOS端使用的是PEM格式的（對DER進行了Base64編碼＋頭尾資訊），所以需要將生成的金鑰檔案做一個格式轉化

// PEM檔案起止字串
public final static String PUBLIC_KEY_BEGIN = "-----BEGIN PUBLIC KEY-----";
public final static String PUBLIC_KEY_END = "-----END PUBLIC KEY-----";
public final static String PRIVATE_KEY_BEGIN = "-----BEGIN RSA PRIVATE KEY-----";
public final static String PRIVATE_KEY_END = "-----END RSA PRIVATE KEY-----";
private static String replaceNewLine(String strText){
//相容linux環境和windows環境
strText = strText.replace("\n","\r\n"); 
String strResult = ""; 
int intStart = 0; 
int intLoc = strText.indexOf("\n", intStart); 
while(intLoc != -1){ strResult += strText.substring(intStart, intLoc - 1); 
intStart = intLoc + 1; intLoc = strText.indexOf("\n", intStart); 
} 
strResult += strText.substring(intStart,strText.length()); 
return strResult;
}
// 轉換為iOS端可使用的PEM祕鑰格式
public static void savePEMPublicKey(RSAPublicKey pubKey,String strPEMKeyFile) { 
String strKey = replaceNewLine(getPublicKeyString(pubKey));
try { 
FileWriter keyFile = new FileWriter(strPEMKeyFile);
PrintWriter out = new PrintWriter(keyFile);
out.println(PUBLIC_KEY_BEGIN);
int keyLength = strKey.length();
int lines = keyLength / 64;
for (int i = 0; i < lines; i++) {
out.println(strKey.substring(i * PEM_LINE_LENGTH, i* PEM_LINE_LENGTH + PEM_LINE_LENGTH));
}
out.println(strKey.substring(lines * PEM_LINE_LENGTH, keyLength));
out.println(PUBLIC_KEY_END); out.close(); 
} 
catch (IOException e) {
e.printStackTrace();
}
}
public static void savePEMPrivateKey(RSAPrivateKey privateKey,String strPEMKeyFile) {
String strKey = replaceNewLine(getPrivateKeyString(privateKey));
try {
FileWriter keyFile = new FileWriter(strPEMKeyFile);
PrintWriter out = new PrintWriter(keyFile);
out.println(PRIVATE_KEY_BEGIN);
int keyLength = strKey.length();
int lines = keyLength / PEM_LINE_LENGTH;
for (int i = 0; i < lines; i++) {
out.println(strKey.substring(i * PEM_LINE_LENGTH, i* PEM_LINE_LENGTH + PEM_LINE_LENGTH));
}
out.println(strKey.substring(lines * PEM_LINE_LENGTH, keyLength));
out.println(PRIVATE_KEY_END);
out.close();} 
catch (IOException e) {
e.printStackTrace();
}}